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Design Considerations for the Implementation of
Green Roofs
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
CONTENTS EXECUTIVE SUMMARY ................................................................................................. I 1.
INTRODUCTION ............................................................................................... 1-1
1.1 1.2
BACKGROUND .................................................................................................................................1-1 SCOPE OF WORK ............................................................................................................................1-1
2.
OVERVIEW OF GREEN ROOFS...................................................................... 2-1
2.1 2.2 2.3 2.4
INTRODUCTION ................................................................................................................................2-1 HISTORY .........................................................................................................................................2-1 WHAT IS A GREEN ROOF AND HOW DOES IT FUNCTION? ..................................................................2-2 GREEN ROOF UPTAKE AND INSTALLATIONS ......................................................................................2-3 BRITISH COLUMBIA ..........................................................................................................................2-3 TORONTO, ONTARIO ........................................................................................................................2-5 PORTLAND, OREGON .......................................................................................................................2-5 OTHER NORTH AMERICAN EXAMPLES...............................................................................................2-6 GERMANY AND CONTINENTAL EUROPE .............................................................................................2-7 THE BENEFITS OF GREEN ROOFS ....................................................................................................2-7 STORMWATER MANAGEMENT ...........................................................................................................2-8 ENERGY EFFICIENCY .....................................................................................................................2-10 URBAN HEAT ISLAND EFFECTS .......................................................................................................2-10 ROOF MEMBRANE DURABILITY .......................................................................................................2-11 AIR QUALITY .................................................................................................................................2-12 AESTHETICS AND PROPERTY VALUES .............................................................................................2-13 URBAN AGRICULTURE ....................................................................................................................2-13 BIODIVERSITY AND HABITAT PRESERVATION ...................................................................................2-14 NOISE ATTENUATION .....................................................................................................................2-14 DEVELOPMENT OF A GREEN ROOF DESIGN RECOMMENDATION .......................................................2-14 IS A GREEN ROOF APPROPRIATE FOR ANY SITE IN METRO VANCOUVER ..........................................2-15
2.5
2.6 2.7
3.
BREAKING DOWN BARRIERS AND TRANSFORMING THE MARKET ........ 3-1
3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8
INTRODUCTION ................................................................................................................................3-1 A BAD REPUTATION FROM THE PAST ...............................................................................................3-1 GREEN ROOF MISPERCEPTION WITH ENVELOPE FAILURES ...............................................................3-2 REPAIRS .........................................................................................................................................3-3 MAINTENANCE ................................................................................................................................3-4 STRUCTURAL ISSUES ......................................................................................................................3-4 AVAILABILITY OF EXPERTISE ...........................................................................................................3-5 SCIENTIFIC RESEARCH ....................................................................................................................3-5 RESEARCH IN CANADA .....................................................................................................................3-6 RESEARCH IN UNITED STATES .......................................................................................................3-11 FEAR OF THE UNKNOWN/“FIRST TO MARKET” RISK .......................................................................3-15 COST ............................................................................................................................................3-15 LACK OF STANDARDS....................................................................................................................3-16 INSURANCE COVERAGE .................................................................................................................3-17 FIRE HAZARD AND UPLIFT .............................................................................................................3-19 ARCHITECTURAL STYLE ................................................................................................................3-19 AESTHETICS .................................................................................................................................3-20 INTERVIEWS WITH DEVELOPERS .....................................................................................................3-21 KEY CONCERNS RAISED IN INFORMAL DISCUSSIONS .......................................................................3-21 HPO GREEN ROOF TASK FORCE REPORT......................................................................................3-22
3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
4.
REGULATORY STORMWATER CONTROL CRITERIA .................................. 4-1
4.1 4.2
INTRODUCTION ................................................................................................................................4-1 THE STORMWATER BENEFIT ............................................................................................................4-1 SALMON HABITAT – CREEK SYSTEMS ...............................................................................................4-1 REDUCTION IN STORMWATER INFRASTRUCTURE ...............................................................................4-2 OVERVIEW OF 2003/2004 GREEN ROOF MONITORING STUDY ...........................................................4-3 IMPACT OF GREEN ROOFS ON REDUCING EFFECTIVE IMPERVIOUS AREA............................................4-3 RECEIVING WATER QUALITY IMPROVEMENTS ...................................................................................4-5 CALCULATING A GREEN ROOF WATER QUALITY SAVING ...................................................................4-5 TIMELINE FOR IMPLEMENTATION .......................................................................................................4-6 REDUCTION IN MAJOR STORM FLOWS AND DEVELOPMENT COST CHARGES ......................................4-7 PROPOSED REDUCTION IN DEVELOPMENT COST CHARGES (DCCS) ..................................................4-7 RE-DEVELOPING AREAS ..................................................................................................................4-8 REDUCTION IN RISKS DUE TO CLIMATE CHANGE ..............................................................................4-8 REDUCING THE STORMWATER IMPACT TO AQUATIC HABITAT ............................................................4-9 ESTABLISHING GREEN ROOF BENEFITS IN DEVELOPING WATERSHEDS ..............................................4-9 ESTABLISHING GREEN ROOF BENEFITS IN RE-DEVELOPING WATERSHEDS .......................................4-10
4.3 4.4
4.5
4.6 4.7
5.
DEVELOPING A BUSINESS CASE FOR GREEN ROOFS ............................. 5-1
5.1 5.2 5.3 5.4
INTRODUCTION ................................................................................................................................5-1 COST-BENEFIT RATIOS ...................................................................................................................5-4 COST OF A CONVENTIONAL ROOF ....................................................................................................5-4 COST OF A GREEN ROOF .................................................................................................................5-4 BASIC COSTS (EXCLUDING STRUCTURAL COSTS) .............................................................................5-4 STRUCTURAL COSTS .......................................................................................................................5-5 TOTAL COSTS .................................................................................................................................5-6 SAVINGS FROM A GREEN ROOF .......................................................................................................5-7 CASE STUDY 1 – “THE SILVA” BUILDING IN NORTH VANCOUVER ......................................................5-9 OVERVIEW OF DEVELOPMENT, CONSTRUCTION AND INSTALLATION ....................................................5-9 TECHNICAL AND DETAILED DESIGN INFORMATION ...........................................................................5-10 OPERATION AND MAINTENANCE REQUIREMENTS .............................................................................5-11 COST OF THE GREEN ROOF (EXCLUDING STRUCTURAL COSTS)........................................................5-11 LESSONS LEARNED .......................................................................................................................5-11 GREEN ROOFS AND MULTI-STOREY TOWERS .................................................................................5-12 CASE STUDY 2 – THE WHITE ROCK OPERATIONS CENTRE..............................................................5-12 TECHNICAL AND DETAILED DESIGN INFORMATION ...........................................................................5-13 COST OF THE GREEN ROOF ...........................................................................................................5-14 LESSONS LEARNED .......................................................................................................................5-14
5.5 5.6
5.7
6.
STRATEGY FOR IMPLEMENTATION AND CONCLUSIONS ......................... 6-1
6.1 6.2 6.3 6.4 6.5
INTRODUCTION ................................................................................................................................6-1 REVIEW OF BUSINESS CASE FOR GREEN ROOFS ..............................................................................6-1 INCENTIVES .....................................................................................................................................6-2 EXISTING GREEN BUILDING INCENTIVES ...........................................................................................6-3 DENSITY BONUS..............................................................................................................................6-3
7.
SUMMARY ........................................................................................................ 7-1
8.
REFERENCES .................................................................................................. 8-1
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
FIGURES Figure 4-1: EIA Versus Growing Medium Depth ...................................................................................4-3 Figure 5-1: Eastern Section of the Silva Building Green Roof ..........................................................5-10 Figure 5-2: The Green Roof at the White Rock Operations Centre...................................................5-13
TABLES Table 3-1: Determination of Potential Green Roof Areas in the City of Vancouver ........................3-19 Table 4-1: Typical Stormwater Criteria1 in Metro Vancouver ..............................................................4-2 Table 4-2: Impact of 150 mm Green Roofs on Major Storm Flows1 ....................................................4-7 Table 4-3: Summary of Estimated Baseline Green Roof Stormwater Savings................................4-11 Table 5-1: Summary of Green Roof Benefits and Benefit Recipients ................................................5-3 Table 5-2: Summary of Basic Green Roof Costs (Metric) ....................................................................5-5 Table 5-3: Summary of Additional Structural Costs.............................................................................5-6 Table 5-4: Total Cost of a Green Roof....................................................................................................5-7 Table 5-5: Details of Green Roof Benefits .............................................................................................5-8 Table 5-6: 150 mm Green Roof Cost-Benefit Analysis Summary .......................................................5-9 Table 5-7: Green Roof Facts for the Silva Building ............................................................................5-10 Table 5-8: Green Roof Construction Costs for the Silva Building ....................................................5-11 Table 5-9: Green Roof Facts for the White Rock Operations Building.............................................5-13
APPENDICES Appendix A Appendix B Appendix C Appendix D Appendix E
Annotated Bibliography Green Roof Design Considerations Summary of Business Case Research Green Roofs and LEED® Resources
Executive Summary
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
EXECUTIVE SUMMARY This report has been developed to provide background information and data to assist regional municipalities and developers in understanding the benefits, issues and costs associated with green roof installations and to provide guidance on where research and the green roof business are headed in the near future. Much of the green roof research, data and technologies to date come from Germany and Europe where green roofs have been encouraged and tracked for more than 40 years. In recent years a great deal of information has become available about green roof design and installation for North America and specifically for the Pacific Northwest climate. Green roof installations in this region are increasing and so is the research data to help guide design and decision-making for green roofs for both the public and private sectors. The most common type of green roof, world-wide, is the extensive green roof, which has the benefit of being lighter, easier to install and less expensive than the other commonly recognized type, the intensive green roof. Extensive green roofs also generally cover far more surface area than the intensive variety. However, in 2002, intensive green roofs outnumbered extensive green roofs in the Metro Vancouver area. The possible benefits of green roofs to an urban area are significant and include: stormwater management, energy savings, urban heat island mitigation, air quality improvement, additional aesthetic and property value, urban agriculture possibilities, increased biodiversity and habitat preservation. Of these, the most significant for Metro Vancouver is likely the stormwater management benefits of green roofs. In this wet climate, stormwater management requirements have increased and changed substantially over the past ten to fifteen years, particularly in land area required to manage stormwater runoff and area’s where combined sewer overflows are a concern. Green roofs also represent a way to mitigate stormwater impacts of development on the building footprint which is typically the largest portion of impervious area on a developed lot. Because of the multiple benefits that green roofs provide to the urban environment, it is reasonable that municipalities provide encouragement for the installation of green roofs in new development and re-development areas. A number of North American cities have already done this in various ways, including: reduction in development cost charges (DCCs), direct incentives (e.g. tax credits) for green roofs, streamlined approvals, density bonuses and permit requirements. Reduction in DCCs appears to be a simple and easily implemented approach and is recommended for municipalities that wish to encourage use of green roofs in urban areas. Research on existing green roof installations and computer modelling of measured green roof runoff were used to develop a baseline green roof case for the Pacific Northwest climate to maximize the stormwater benefits. The baseline case of a single layer extensive green roof with 150 mm of growing medium was then used to evaluate the costs of installation, including structural upgrade, relative to the benefits and the possible offsets of the green roof. The estimates of cost show that a green roof is currently likely to cost at least 50% more than a conventional flat roof, even when financial benefits and incentives in the form of reduction in
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
DCCs are assumed. But recent reports on costs for installed green roofs in North America (e.g. Toronto) indicate costs may be starting to come down as a result of increased availability of green roof design and installation experience. A recent study for the City of Portland attempted to evaluate private and public benefits of a green roof and found significant net benefit values for both sectors over the 40-year lifespan of the roof. The Portland study also noted, however, that at the 5-year point, there was still a net private cost, rather than a benefit. The cost studies in this report examined only direct costs and directly attributable benefits, but not the value of intangible benefits or energy savings which vary widely for individual cases. Green roofs provide a wide range of possible benefits for a dense and growing urban area such as the Metro Vancouver region. Many municipalities within the region already require stormwater source controls for new and re-development to mitigate the hydrologic impacts of urbanization. Green roofs can be a useful source control that does not require dedication of valuable ground surface area. Savings in energy from green roofs due to reduced heating and cooling needs play into the goals of energy efficiency and conservation to reduce the need for energy production as well as reducing climate change impacts by reducing carbon emissions from energy production. Other urban benefits of green roofs such as air quality improvements, heat island mitigation, improved aesthetics of the urban landscape, improved property values, increased habitat for birds and insects and increased bio-diversity, all speak to public values and principles of sustainability that benefit from the increased use of green roofs in the Metro Vancouver region.
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Section 1
Introduction
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
1. INTRODUCTION 1.1
BACKGROUND Although green roofs have been built in Metro Vancouver for more than 35 years they primarily focused on the aesthetic qualities provided by intensive green roof designs. Currently, Metro Vancouver has over 600 green roofs, but installation in the area remains the exception rather than the norm. However, in some countries, such as Germany and Japan, green roofs have become mainstream. After more than 40 years of increasingly advanced technical research, regulatory reform and practical experience green roofs are gaining increased recognition and application in North America. Helping this cause and led in part by developer-innovators and buoyed by an awakening public and political consciousness, is a market transformation towards “green”, including green infrastructure and green building practices. The monetary values for green roof costs and benefits used in this publication to develop a business case are in flux. Supply and installation costs for green roofs have been dropping for years while the capital and total costs of conventional roofs have been rising. At the same time, fast growing technical knowledge in building trades and professions, as well as increasing product availability, sophistication and integration, are all creating a dynamic situation in the industry. This makes it difficult to assign a static value to costs and benefits that should otherwise be easily quantifiable. The numbers derived in this publication are from actual projects in the Lower Mainland of B.C. and used to develop the business case. The costs reflect a best estimate of where the market was in 2005, when the original data was collected.
1.2
SCOPE OF WORK This publication is in three parts, each of which investigates and discusses the benefits of green roofs from a different perspective. The scope of work for the project is described below. The first part of the publication, comprising sections 1 to 3, provides technical information. The purpose of these sections is to provide a detailed overview of green roofs, including information on their applicability, assumed design, installation and function. The information in this section includes:
an explanation of what a green roof is and how it functions; the regional, social and operational performance benefits of green roofs; general green roof design principles; the regional barriers to installation of green roofs; and how to specify and include features that deliver the benefits of green roofs.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
The second part of the publication consists of a business case for installing a green roof rather than a conventional roof. Section 5 determines the impact a green roof has on a development’s marketability, liveability and desirability. The information in this section includes:
relevant studies and research providing hard costs to the more quantifiable benefits of green roofs as relevant within Metro Vancouver;
definition of the costs associated with installing a green versus a conventional roof and quantification of the savings resulting from the societal, operational and regional benefits provided by green roofs; and
a comparison of the structural and design considerations required to install a green roof relative to a conventional roof and the implications to the life cycle costs of the roof.
Section 5 also presents two case studies. The purpose of section 5 is to integrate and contextualize information presented in the previous sections. The case studies highlight technical real costs and barriers of how a green roof is engineered, specified and constructed and illustrate the social, economic and environmental desirability of green roofs. The information in this section includes:
utilization of case studies to show the costs of a green roof; explanation of ongoing operational and maintenance requirements; reviews of issues and lessons learned; and highlights of unique situations or problem-solving successes.
The final section, section 6 of the publication, concludes this report and includes possible strategies for increasing the green roof area in Metro Vancouver.
1-2
Section 2
Overview of Green Roofs
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
2.
OVERVIEW OF GREEN ROOFS
2.1
INTRODUCTION This section of the report begins with a general history of green roof applications. The definition and function of a modern green roof will be explained and the extent of green roof technology world-wide and in Metro Vancouver will be presented. This section will describe the benefits of green roofs and present the design standard required to achieve these benefits. Finally, the applicability of green roofs throughout Metro Vancouver will be discussed. Some of the information presented in this section has already been published in the Metro Vancouver document “Stormwater Source Control Preliminary Design Guidelines”1 and in the Public Works and Government Services Canada document “Green Roof Waterproofing: Expertise from Germany”.2 An annotated bibliography of the references that were investigated to produce this publication is provided in Appendix A.
2.2
HISTORY Green roofs can be traced back through time beginning with the Hanging Gardens of Babylon. Constructed around 605 BC, the Hanging Gardens have been identified as one of the seven ancient wonders of the world. They are described in written records and have been confirmed by archaeological evidence. One record states that the Hanging Gardens: … consist of vaulted terraces raised one above another, and resting upon cube-shaped pillars. These are hollow and filled with earth to allow trees of the largest size to be planted. The pillars, the vaults, and terraces are constructed of baked brick and asphalt.
Another record states that: … platforms on which the garden stood consisted of huge slabs of stone (otherwise unheard of in Babel), covered with layers of reed, asphalt and tiles. Over this was put “a covering with sheets of lead, that the wet which drenched through the earth might not rot the foundation. Upon all these was laid earth of a convenient depth, sufficient for the growth of the greatest trees. When the soil was laid even and smooth, it was planted with all sorts of trees, which both for greatness and beauty might delight the spectators.”
1
Lanarc et. al., 2004
2
Ngan, 2003
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
More recently, the relatively high industrialization and dense populations in European countries have led them to develop a strong environmental consciousness many years ahead of North Americans. Europeans now have 40 years of technical and practical experience with green roof construction and maintenance. In particular, Germany has emerged as a world leader in green roof technology and now, one out of every seven new roofs in Germany is green3. In the Lower Mainland of B.C., many ground level green roofs were initially built in conjunction with the development of underground parking garages. Others were built as roof gardens or deck garden features. These intensive green roofs were built primarily to provide pleasing urban green space. Since the 1970s, the construction of green roofs has been increasing, motivated by ecological benefits as well as aesthetic desirability. There are now over 600 green roofs in the Lower Mainland4.
2.3
WHAT IS A GREEN ROOF AND HOW DOES IT FUNCTION? A modern green roof is simply a conventional roof with layers of drainage and vegetated growing medium installed on top of the waterproofing membrane. Typically, two types of green roof are defined, extensive and intensive. Extensive green roofs mimic nature and require very little external input for either maintenance or propagation. The plants, normally mosses, succulents, herbaceous plants and grasses, are carefully chosen to be able to regenerate and maintain themselves over long periods of time, as well as to withstand the harsh conditions on rooftops such as exposure to extreme cold, heat, drought and wind. Extensive green roofs have a relatively shallow layer of lightweight growing medium that is low in organic material and high in mineral substrate. In general, the growing medium is about 2 – 15 cm thick with a saturated system pressure of 0.5 – 3.0 kPa. Because of the low structural capacity required, extensive systems may not require structural upgrades and therefore are particularly suited for retrofits. They typically do not require irrigation, and are usually inaccessible to the public. Intensive green roofs in comparison to extensive are usually constructed where public access and recreational use are a primary function. These roofs have a deeper growing medium than extensive roofs, with a higher organic content, and can support lawns, large plants, trees and outdoor furnishings. The growing medium depth ranges from 20 cm to 100 cm or more, with saturated system pressures of over 4 kPa. Because of the high structural capacity involved, intensive green roofs are almost always incorporated in the building plan at the design stage as structural upgrade afterwards can be expensive and
3
Hämmerle, Fritz. “Grün wächst” in DDH Das Dachdecker-Handwerk Heft 14/02. pp.22-24
4
Davis, Kim. 2002. Green Roof Inventory: Preface Report. Report prepared for the Greater Vancouver Regional District, December 12, 2002
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
impractical. Like gardens on the ground, intensive systems require ongoing maintenance, including regular irrigation, weeding and fertilization. Intensive green roofs such as landscaped roofs and garden terraces have been installed in the Metro Vancouver region for the past 35 years. However, extensive green roofs have been gaining popularity in BC in the past 10 years because of light weight, low maintenance and the multiple benefits offered to the urban areas. The focus of this document is on extensive green roofs because these roofs provide a wide range of benefits for minimal cost, with only minor changes to conventional construction and no additional effort over the long term. In contrast, intensive green roofs generally have higher costs for structural upgrades, materials and for ongoing operation and maintenance than extensive green roofs.
2.4
GREEN ROOF UPTAKE AND INSTALLATIONS BRITISH COLUMBIA Davis identified over 600 green roof installations in the Lower Mainland of B.C.5 The majority of these installations are intensive green roofs but there are several examples of extensive and semi-extensive green roofs constructed over the last decade. Many extensive green roofs have been installed since the inventory was completed in 2002. Some examples of recently completed and upcoming installations of extensive green roof systems in BC are as follows:
Operations Centre, White Rock; Justice Building, Sechelt; Motion Capture Building at Electronic Arts, Burnaby; Firehall, Richmond; Arts and Social Sciences Complex at Simon Fraser University, Burnaby; Information Centre, Whistler; The Verana, Penticton; Vantana, North Vancouver; Musee, Vancouver; Vancouver Convention and Exhibition Centre, Vancouver; Vancouver Police Department Training Facility, Vancouver (scheduled for 2009); Broadway Technology Centre, Vancouver (scheduled for 2009); and Millennium Water, Vancouver (scheduled for 2009).
Although most extensive green roofs in BC are installed on public or institutional buildings, the number of installation in private developments is increasing. Because of the increase in public awareness on green roof benefits and the availability of lightweight,
5
Davis, Kim, 2002
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
low maintenance green roof systems, there is a growing demand for green roof installation on private residences in the Lower Mainland.6 Although Metro Vancouver and the various municipalities in the Lower Mainland support sustainability, there are presently no directives or incentives to encourage green roof installations in the region. The City of Port Coquitlam is the first city in BC to formally incorporate green roofs as part of its sustainability initiative. The council approved a zoning bylaw in December 2006 that requires green roofs for all large format buildings over 5000 m2. The main purposes of the bylaw are to achieve environmental benefits from green roofs such as stormwater management, energy savings and urban heat island mitigation and to beautify the city with greenery. The City of Vancouver is proposing a similar bylaw for 2009. The City of Richmond approved a new Bylaw 8385, “Green Roofs and Other Options Involving Industrial and Office Buildings Outside the City Centre” in September 2008. The current proposal for the bylaw specifies that use of a green roof on at least 75% of a building’s area can be used as a method of achieving stormwater management goals on commercial and industrial buildings of 2000 m2 or more. Of the several recent projects in the Metro Vancouver area, two are particularly significant for the evolution in the use of green roofs in the region. The Vancouver Convention Centre Expansion Project (VCCEP) in the downtown core will implement the largest green roof yet built in Canada. The project comprises approximately 2.4 hectares of extensive green roof planted with a variety of native plant species and located on a sloped, rather than flat, roof.7 As a large and highly visible green roof installation, this project is expected to increase public awareness and interest in green roof implementation. The Millennium Water project is another significant milestone for the region. As part of the Athlete’s Village construction for the Vancouver 2010 Olympics, the City of Vancouver required that green roofs be implemented as part of the development. Building insurance has been a challenge for green roof installations in BC. Up until 2007, the four major home warranty insurance companies in BC had been cautious in undertaking insurance on buildings with green roofs. The BC Homeowner Protection Office organized a conference to bring together stakeholders in May 2007 to address and attempt to resolve the issues and several of them were addressed at that time (see section 3.12), but insurance for strata-owned residential structures with green roofs has been virtually impossible to obtain. The Millennium Water project received a commitment
6
7
Schmidt, 2008 Gilbert, Richard; “New Vancouver Trade and Convention Centre Features North America’s Largest Green Roof”, Journal of Commerce, February 29, 2008. URL: http://www.journalofcommerce.com/article/id26657 (Note - the title of the article is factually incorrect and the VCCEP is not North America’s Largest Green Roof).
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
from a major insurer for the post-Olympic use of the building prior to moving forward and represents an important initial success over this obstacle for the region.8 TORONTO, ONTARIO The City of Toronto is one of the first cities in Canada to promote green roofs through financial incentives. The Council approved a Green Roof Incentive Pilot Program in 2006 that offered a financial incentive of $10/m2 for eligible green roof area. Toronto Water funded and administrated the program, which supported the Wet Weather Flow Master Plan. The main objective was to reduce stormwater runoff through green roofs as a source control. The pilot program also aimed to showcase a variety of green roof types and planting styles. To increase uptake in the industrial sector, the Council approved a measure to increase the incentive to $20/m2 for eligible green roof area up to a maximum of $10,000 for single family homes and $50/m2 up to a maximum of $100,000 for industrial, commercial and multi-family residential buildings in the City of Toronto. An eligible green roof requires at least 50% footprint with a growing medium depth of at least 150 mm on a roof slope of less than 10% and be installed over heated space. Other green roofs can be considered eligible if the applicant can show equivalency with respect to runoff coefficient and plant survivability. The pilot program was extended and approved 30 successful applications in 2007/2008. Successful applications included single-family residential, institutional and commercial buildings. The City plans to merge the Green Roof Pilot Program with a more comprehensive program of renewable incentives and rename it the Eco-Roofs Incentive Program in 2009, to be administrated by the Toronto Environment Office. This program will better address other benefits of green roofs in addition to stormwater management. In addition, the city is working on building code requirements for a green roof standard for renovation and new construction in Toronto. The City also plans to implement a new bylaw to require green roofs and govern their construction by late 2008.9 PORTLAND, OREGON The City of Portland, Oregon is considered as one of the leaders in promoting green roofs, or eco-roofs, in North America. The Bureau of Environmental Services at Portland has conducted several pilot projects in the city to prove that eco-roofs are an effective source control tool in stormwater management for Portland. A green roof can mitigate roof runoff and thus lower the occurrence of combined sewage overflow events during heavy rainstorms, reducing water pollution in receiving rivers.
8
Ian Smith, City of Vancouver; telephone communication, May 2008.
9
URL: http://www.toronto.ca/greenroofs/
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Portland promotes green roofs through a number of policies. Internally, it requires all new city-owned public buildings to have a green roof that covers at least 70% of the roof. Roof replacement must also include a green roof when practical. To encourage green roof adoption on private buildings, the City offers developers a floor area bonus through its Floor Area Ratio Bonus Planning and Zoning Code. Basically, the larger the green roof, the larger the bonus offered. The City also offers discount for building owners that manage stormwater on their own properties and green roofs is one of the tools for on-site stormwater management. The City allows either type of green roof, as long as it has a minimum depth of growing medium or 4 inches. In addition to financial incentives through density bonus and discount in stormwater fees, Portland also provides technical resources to help building owners install green roofs. It funds various green roof demonstrations and research projects to provide technical data to support its initiatives and provides education and outreach programs to increase public awareness of the various benefits of green roofs.10 OTHER NORTH AMERICAN EXAMPLES Green roofs are gaining acceptance and advocates across the continent and construction of green roofs grew 30% in North America in 200711. Other areas in North America that are encouraging installation of green roofs using various incentive and regulatory approaches include:
New York City, New York – The New York State Legislature recently enacted a bill12 to provide a one-time tax credit of $48 USD per square metre for a qualifying green roof installed on a building in New York City. The incentive is available for new construction and renovation projects, and is intended to defray approximately 35% of the additional cost of installing a green roof rather than a standard roof; Chicago, Illinois – The City of Chicago instituted a green roof grant program in 2001 and constructed a green roof on the Chicago City Hall the same year. Chicago leads the U.S. in area of green roofs installed with 48,090 square metres of green roofs added in 2007.13 Other prominent Chicago buildings with green roofs include the Michigan Avenue Apple Store, the Chicago Center for Green Technology, and the Peggy Notebaert Nature Museum. Millennium Park, at 9.9 hectares, is one of the largest intensive green roofs in the world and covers two parking garages, a transit center and a 1,525-seat indoor performance center14;
10
URL: http://www.portlandonline.com/BES/index.cfm?c=44422&
11
3rd annual Green Roof Market Industry Survey, by the Toronto-based non-profit group Green Roofs for Healthy Cities
12
New York State Assembly Bill A11226 (same as S7553), sponsored by Bronx Assemblyman Ruben Diaz
13
Anderson, Lisa, “Green roofs are taking root in American cities”; Chicago Tribune, September 19, 2008.
14
URL: http://www.greenroofs.com/projects/pview.php?id=459
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Michigan – The Ford Motor Company Truck Manufacturing Facility in Dearborn Michigan has a 4.2-hectare green roof which was primarily designed to reduce air pollution in this region. A green roof research program at Michigan State University was initiated in collaboration with Ford Motor Company during 2000 in an effort to advise them on the installation of the truck plant’s roof and the program continues to support green roof research and education in Michigan.
GERMANY AND CONTINENTAL EUROPE Green roof standards are well established in Europe and for many years, the publication by the Forschungsgesellschaft Landschaftsentwicklung Landscaftsbau (FLL) Guidelines for the Planning, Execution and Upkeep of Green Roof Sites has been the main reference for green roof designers. The FLL is the governing body which issues guidelines for green roof installation practices in Germany. Growing environmental concerns in urban areas in the 1970s, created opportunities for the introduction of a number of environmental advancements in Germany, and among them were green roofs. Green roof technology was quickly embraced because of its broad-ranging environmental benefits and aesthetic appeal in a time of increasing environmental consciousness. Many German cities have since introduced incentive programs to promote green-roof technology and improve environmental standards. Building law now requires the construction of green roofs in many urban centers. This type of regulatory encouragement resulted in extensive implementation and success of green roof applications throughout Germany.15 German experience with green roofs (called Dachbegrünung) over the past 30 years has provided the base for modern green roof technology. Green roofs are installed in about 1 in 7 of all new and retrofitted flat roofs in the country16. In 2001, this translated into 13.5 million m². In Berlin, where many developments require them, 30% of all new flat roofs are greened17. Extensive green roofs are also commonplace in the Netherlands, Belgium, France, Austria, Norway, Switzerland and other European states.18
2.5
THE BENEFITS OF GREEN ROOFS Green roofs offer multiple benefits to urban areas. While some of the benefits can be quantified and assigned financial values, other benefits are intangible and their values are difficult to quantify objectively. This section of the report summarizes the major benefits of green roofs regardless of when, to whom, or with what value the benefit accrues. A detailed analysis of the latter characteristics is provided in section 4.
15
Oberndorfer, 2007.
16
Hämmerle, Fritz. “Grün wächst” in DDH Das Dachdecker-Handwerk Heft 14/02. pp.22-24
17
Podium discussion in proceedings from Infoforum Regenmanagement, Berlin 2000. p.80
18
Peck, 2004
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
STORMWATER MANAGEMENT Urban development increases impervious surfaces such as paved roads and rooftops and changes the hydrology in the urban areas. In natural landscape, rainfall and snowmelt infiltrate through the pervious surfaces into the ground with little surface runoff. However, in urban areas stormwater from impervious surfaces runs off and flows into the drainage system with little infiltration. It picks up contaminants such as heavy metals, oil and grease from pavements and rooftops on the way. Therefore, tools such as source controls, detention facilities and stormwater treatment units are used to manage the volume, flow rate and quality of stormwater in urban areas. Green roofs can convert impervious rooftops into pervious surfaces that absorb water and release it slowly over a period of time. Some of the water is taken up by the vegetation and released back to the atmosphere through evapotranspiration. Excess water is discharged from the system to the roof drain. Graham and Kim19 conducted a simulation study in Vancouver to examine the potential of green roofs as stormwater management tools. Their simulation results show that green roofs, both extensive and intensive systems, are potentially very effective at reducing volumes and peak rates of runoff from developed areas. The combination of green roofs and ground-based infiltration facilities was shown to be the most effective overall source control strategy for the Metro Vancouver region. The water retention capacity of a green roof depends on the system configuration, including roof slope, type and depth of growing medium, vegetation types and coverage and the local climate characteristics such as temperature, humidity, rainfall intensity and frequency.20 The FLL green roof guidelines provide useful information for the design of green roofs for runoff retention. The FLL Green Roof Guidelines show that the coefficient of discharge generally decreases with growing medium depth.21 The coefficient of discharge is based on the ratio between drainage volume and rainfall volume during a standard block of rain. A higher coefficient of discharge results in greater runoff and thus less retention. For roof slopes up to 15o, the coefficient of discharge reduces from 0.7 at 2 - 4 cm depth of medium to 0.1 at > 50 cm depth of medium. At the same depth of medium, the coefficient of discharge increases slightly for roof slopes greater than 15o. The FLL green roof guidelines also showed that the annual average water retention increases with depth of medium and different types of vegetation.22 The annual average water retention increases from 40% for moss-sedum vegetation on 2 – 4 cm depth of 19
Graham, P. And Kim, M. (2003) “Evaluating the Stormwater Management Benefits of Green Roofs Through Water Balance Modeling”, Greening Rooftops for Sustainable Communities, Chicago, IL
20
Monterusso, 2003
21
FLL, 2002
1
22
FLL, 2002
2
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growing medium to 60% for grass-herbaceous plants on >15 – 20 cm depth of medium. Note that annual water retention figures were obtained from various German locations with annual precipitation values of 650 – 800 mm over several years. The FLL guidelines for water retention only apply to those regions with similar climate patterns. For regions with lower annual precipitation, higher water retention is expected and vice versa. Connelly showed that the retention of green roofs in Vancouver23 was 86 - 94% of rainfall between April and September, while they retained only 13 – 18% between October and March. Similar results were observed by Liptan who showed that the retention of a green roof in Portland Oregon was 59% between December and March while the retention was 92% from April to November24. The cool, wet winters on the west coast mean that evapotranspiration rates, and therefore the retention rate of green roofs, are lower in the winter months. Liu observed that green roofs can attenuate runoff peak flows.25 The amount of attenuation depends on the intensity of the rain event. Hutchinson also noted that the green roof can attenuate the peak runoff even when the substrate is saturated during the winter months.26 Monitoring of the Vancouver Public Library Green Roof showed that peak flow reduction was approximately 30% for smaller winter events, but only 5% for large winter storm events.27 Rowe showed that extensive green roofs could retain 61% of total rainfall on average in Michigan. However, the percent retention also depends on the rainfall intensity. The green roofs were more effective in light rainfall than heavy rainfall28. Green roofs have been shown to affect the quality of runoff. While green roofs can filter out certain chemicals, the substrate can also act as a source of contaminants.29 Water quality analysis at the York University green roof showed that the total loads of most pollutants of concern were lower from the green roof than from the control roof.30 However, the green roof runoff showed higher levels of phosphorus, which is likely due to leaching from the soil. Phosphorous was also observed in the runoff from other green roofs.31 Based on analyses done on several green roofs in Sweden, Czemiel Berndtsson
23
Connelly, 2006
24
Liptan, 2003
25
Liu, 2003
26
Hutchinson, 2003
27
Johnston, 2004
28
Rowe, 2003
29
Czemiel Berndtsson
30
Macmillan, 2006
31
Hutchinson, 2003
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
concluded that the green roofs behaved as a source of phosphate phosphorus, a minor source of total nitrogen and as a sink for nitrate nitrogen.32 ENERGY EFFICIENCY Green roofs increase the energy efficiency of the building envelope and reduce a building’s energy demand on space conditioning and therefore greenhouse gas emissions, through direct shading of the roof, evapotranspiration and improved insulation values.33 Green roofs are particularly effective in reducing heat entry into the building in the summer. The plants shade and cool the roof. The insulation value is in both the plants and the growing medium.34 Water in the plants and the growing medium evaporates and further cools the roof. The growing medium also acts as a thermal mass that stores solar energy during the day and releases it at night. Green roofs are less effective in preventing heat leaving the building in the winter due to the limits of the same thermal mechanisms. Minke showed that a 200 mm layer of growing medium and a 200-400 mm layer of thick grass have a combined insulation value equivalent to 150 mm mineral wool insulation (RSI 0.14).35 An experimental study by Oak Ridge National Laboratory demonstrated that a vegetated roof of 0.46-0.76m of soil reduced the peak sensible cooling needs of a building by about 25%.36 The National Research Council of Canada showed that an extensive green roof with grass planted on a 150 mm growing medium reduced the heat flow through the roof by over 75% in the spring and summer in Ottawa.37 Also, the roof membrane underneath the green roof rarely reached above 30°C compared to an exposed membrane that typically reached over 60°C in the summer. The British Columbia Institute of Technology’s Centre for the Advancement of Green Roof Technology found that extensive roofs in Vancouver reduced the heat flow through the roof by over 80% in the summer and by about 40% in the winter. The same study found that the median membrane temperature fluctuation reduced from 48ºC to less than 5ºC.38 Temperature measurements on an intensive green roof in Singapore also confirmed the cooling effects of the plants and the growing medium.39 URBAN HEAT ISLAND EFFECTS
32
Czemiel Berndtsson
33
Minke, 1982; Christian, 1996; Eumorfopoulu, 1998; Palomo Del Barrio, 1998; Environmental Building News, 2001
34
Palomo Del Barrio, 1998 and Eumorfopoulu, 1998
35
Minke, 1982
36
Christian, 1996
37
Liu, 2003
38
Connelly, 2006
39
Tan, 2003
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
The urban heat island refers to the higher air temperature in the city centre compared to the surrounding natural landscape. The difference in temperature is usually in the range of 2-3ºC. The lack of vegetation cover and natural landscape in the city means the city experiences less evaporative cooling and therefore increases the air temperature.40 Dark building materials such as rooftops and pavements further absorb and trap solar heat and these factors combine to contribute to the urban heat island. Many ways have been proposed to modify the urban surface to mitigate the urban heat island effect, including urban forestry, green roofs and white roofs. A white roof has increased reflectivity of the roof surface and reduced daytime net energy input from the sun.41 Green roofs convert the incoming solar energy into latent heat through the process of evapotranspiration by vegetation, which results in a cooler surface.42 Temperature measurements showed that vegetation could reduce the surface temperature and that the extent of reduction depends on the foliage density of the vegetation.43 Bass44 used a Mesoscale Compressible Community Model to illustrate the potential impacts of green roofs on the urban heat island effect in the City of Toronto. A simulation was conducted over a 48 hour period in June 2001 when the air temperature was high. The model showed a 2-3ºC increase in urban temperature compared to the surrounding area. Simulation results showed that irrigation of the city reduced low-level urban temperatures by 1°C. The addition of irrigated green roofs, located in the downtown area, further increased the cooling to 2°C and extended the 1°C cooling region over a larger geographic area. The simulation showed that with sufficient moisture for evapotranspiration, green roofs can play a role in reducing the urban heat island effect. ROOF MEMBRANE DURABILITY Experience from Europe shows that a green roof can double the life span of a conventional roof by protecting the membrane from extreme temperature fluctuations, ultraviolet radiation and mechanical damage.45 Porsche claimed that a roof covered with plantings can be expected to outlast a conventional roof by a factor of at least two.46 German experience showed that modern green roof planting systems will last over 50 years. Old green roofs in Berlin demonstrated a life span of more than 90 years before they require major repair or replacement.
40
Sailor, 1995
41
Akbari, 2001
42
Bass, 2001
43
Tan, 2003
44
Bass, 2002
45
Peck & Kuhn, 2001
46
Porsche, 2003
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Liu showed that the surface temperature of an exposed roof membrane reached over 60ºC on a hot summer day in Ottawa, Ontario. Under a green roof with 150 mm of growing medium and grass, the roof membrane did not reach 30ºC.47 This reduced the rate of heat aging that degrades roof membranes. In addition, the green roof lowered the daily temperature fluctuations on the roof membrane from a median value of 45ºC to less than 5ºC in the summer, greatly reducing the thermal stresses on the roof membrane. These observations suggested that green roofs can make the roof membrane last longer thereby requiring less re-roofing over the structure’s lifetime. This not only saves money for the owner, it also reduces material wastes potentially going to landfill. AIR QUALITY Plant surfaces adsorb airborne particles and remove them from the air. The particles are washed off the leaves and into the growing substrate during rain events. An UK study48 estimated that 2000 m2 of uncut grass on a roof could remove as much as 4000 kg of particulates from the surrounding air by trapping it on its foliage. Trees, shrubs and smaller plants on green roofs can adsorb air pollutants, thus improving air quality in urban areas. A pilot study in Singapore noted that green roofs can reduce sulphur dioxide by 37% and nitrous acid by 21%.49 However, the researchers also recorded an increase in nitric acid and particulate (PM 2.5 and 10) likely from gravel ballast and bare spots on the green roof. Currie used the Urban Forest Effects (UFORE) model developed by the United States Forest Service to simulate the air purifying potential of green roofs in Toronto by examining the levels of NO2, SO2, CO, PM10 and ozone in different vegetation scenarios.50 The study showed that although trees have significantly high potential in addressing air pollution in Toronto, green roofs planted with grass could provide considerable mitigation as well. Green roofs and reflective roofs can also reduce summertime peak cooling demand therefore indirectly reducing CO2 emissions from power plants due to lower energy demand.51 This is particularly important for air quality in regions that generate electricity through coal combustion. Ryerson University researchers estimated green roofs could potentially save up to $2.5 million annually for the City of Toronto due to improvement in air quality.52 47
Liu, 2003
48
Johnston, 1996
49
Yok, 2005
50
Currie, 2005
51
Akbari, 2001
52
Banting, 2005
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
AESTHETICS AND PROPERTY VALUES Rooftops are perhaps the most underutilized space in cities. Green roofs not only make use of this space by providing much needed recreational green space for city dwellers and living space for birds and insects; they often improve the architectural aesthetic of the building, therefore increasing the overall property value. German statistics showed that green roofs, particularly intensive green roofs that are designed to provide visual interests and passive recreational space for occupants, can increase rental value of office buildings.53 In Germany, the increase in property value alone often can justify the installation of a green roof. In Germany, building owners have to pay stormwater fees depending on the impervious area on site. Green roofs absorb rain water and reduce site runoff, thus qualifying for discounted stormwater fees. The discount depends on the size and design (and thus the runoff coefficient) of the green roof. Therefore, buildings with green roofs are often of higher value due to the reduced annual stormwater fees. URBAN AGRICULTURE Green roofs can provide secured growing space for gardening and agriculture in urban areas. They have the potential to address the balance between urban spaces for living and growing – an essential component of improving living quality in high density urban areas.54 In Vancouver, the intensive green roof on the terrace roof at the Fairmont Waterfront Hotel produces herbs, vegetables, fruits and edible flowers for the hotel’s restaurant – saving an estimated $25,000 - $30,000 yearly.55 Edible plants include chives, pansies, sorrel and tulips. The savings in cost of herbs and produce more than offsets the garden maintenance cost of about $16,000 annually. In Vancouver, land value is at a premium and there is little space for gardening on the ground. There are often long waiting lists for community garden plots in the city. Rooftops offer excellent opportunities for urban agriculture. The City Farmer, a Vancouver based group promoting urban agriculture, provides resources on growing produce on rooftops.56 The students in Environmental Sciences at the Université du Québec à Montréal created a rooftop garden to grow food. The goal of the project was to allow students to explore urban agricultural opportunities. The produce from the garden are distributed to the 53
Porsche, 2003
54
Kongshaung, 2004
55
CMHC, 2002
56
URL: http://www.cityfarmer.org/subrooftops.html
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
homeless. The group supplies “Ready-to-Grow” kits and guides to promote urban agriculture on rooftops.57 BIODIVERSITY AND HABITAT PRESERVATION The expanding encroachment of urbanization has created an environment of lifeless concrete within our human communities. This sterile world has had a devastating effect on the natural environment. Isolated and manicured parks within city boundaries do little to alleviate the threat to dwindling populations of song birds, plants and other endangered wildlife. Green roofs can provide habitats for birds, insects, native plants and rare or endangered species.58 Inaccessible extensive green roofs, allowed to flourish with minimal human intervention, can be designed to create safe havens and provide wildlife corridors in the urban area for birds and insects. Considerations should be made to provide shelter, food and water to create a suitable living environment. By choosing native plants for landscaping on rooftops the biodiversity of the area can be greatly enhanced by creating food and shelter as well as providing passage ways for wildlife to travel from one area to another. An excellent example of how quickly wildlife can become established on a green roof is the Ford Truck Assembly Plant at Dearborn, Michigan where birds were observed to nest on the roof only weeks after the installation was completed.59 A variety of insect species such as bees, butterflies and beetles are also commonly observed on the Ford green roof. NOISE ATTENUATION There are few research studies indicating the benefits of green roofs at muffling and attenuating urban noise. At the British Columbia Institute of Technology (BCIT), Connelly and Hodgeson60 studied the noise attenuation capacity of two 33 m2 extensive green roof reference plots relative to a control section of conventional flat roof to determine the differences. While the study had to be performed outside in open air, rather than in an acoustically controlled environment, the background noise was minimized by careful timing of the testing during calm periods and at night. The study found that the green roof plots reduced noise transmission by 5 to 13 decibels (dB) over the low to mid frequency range and by 2 to 8 dB over the mid to high frequency range.
2.6
DEVELOPMENT OF A GREEN ROOF DESIGN RECOMMENDATION With green roofs now emerging as a best management practice in North America, many suppliers, trades people and building professionals are newly expanding their services to include this feature. The market is developing, and as might be expected, green roofs
57
URL: http://www.rooftopgardens.ca/
58
Brenneisen, 2003; Gedge, 2003
59
Schmidt, 2008
60
Connelly and Hodgeson, 2008
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
with varying thickness, growing media, plants and other details are being designed and constructed. The purpose of this report is not to provide detailed design guidelines; however, in order to consistently compare the costs and benefits of green roofs, a standard green roof type has to be defined. Furthermore, although any functioning green roof will provide some benefits over a conventional roof, there should be a baseline green roof standard that optimizes value over cost. In a recent project by the Metro Vancouver Stormwater Inter-Governmental Liaison Group (SILG), extensive green roofs were identified as one of five stormwater source control best management practices. The “Stormwater Source Controls Preliminary Design Guidelines” Interim Report61 includes preliminary design guidelines for an extensive green roof. Stormwater control is the primary depth-dependent benefit of green roofs in Metro Vancouver and for this reason, the green roof standard presented in the Metro Vancouver guidelines is adopted in this report also. The baseline green roof standard is an extensive green roof system consisting of the following principal components: plants, growing medium, drainage layer, protection layer and waterproof membrane. The growing medium layer should have a thickness or depth of 150 mm, as discussed in section 4.3. The design considerations presented in the Metro Vancouver “Stormwater Source Controls Preliminary Design Guidelines” (2004) are included in this report in Appendix B.
2.7
IS A GREEN ROOF APPROPRIATE FOR ANY SITE IN METRO VANCOUVER Green roofs – in particular light-weight extensive green roofs – are suitable for most rooftops in Metro Vancouver, including warehouses, office complexes, hospitals, schools, institutional buildings, single and multifamily residential developments and garages. Green roofs must be designed with an awareness of the loading of the roof on the underlying structure. However, use of lightweight growing media has created solutions where the saturated weight of growing media can be added without structural upgrading beyond the standard requirements, especially in concrete buildings or new construction.62 Extensive green roofs have been installed on existing buildings without structural upgrading, but only in cases where the green roof load has been approved for the existing structure by a structural engineer. A green roof designed to provide specific energy or stormwater benefits will likely require more than minimum thickness and weight and some level of structural upgrade to support it. In all cases, the structural load will need to be assessed by an experienced structural engineer. Structural aspects of green roof design are discussed in detail in section 5.4.
61
Metro Vancouver, 2004
62
Peck & Kuhn, 2001
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Most applications of green roofs are on flat roofs (i.e. 2% roof slope). With proper design, green roof systems can be applied to roofs of 20º slope or more.63 Special precautions should be considered to prevent shearing and sliding of green roof materials and plantings. Green roofs are not recommended for slope over 45º due to the danger of shearing and sliding.64 Green roof layers may be applied over inverted or traditional roofing systems. Note however, that it is critical that green roof systems include a root penetration barrier to provide long term protection of the roofing membrane. Shingle and tile roofs are not suitable for greening because these roofs function by shedding water but they are not waterproof.65
63
Peck & Kuhn, 2001
64
FLL, 2002
65
FLL, 2002
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Section 3
Breaking Down Barriers and Transforming the Market
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
3. BREAKING DOWN BARRIERS AND TRANSFORMING THE MARKET 3.1
INTRODUCTION This section discusses and where possible suggests strategies to break down barriers to designing and installing green roofs that exist in North America. The barriers can generally be grouped into four categories: 1. Misconceptions arise due to a lack of correct information and prevent builders from considering a green roof. Misconceptions can be resolved through education. 2. Improper design results from insufficient technical knowledge and/or attempts to reduce cost by cutting corners. Improper design leads to problems or failure and fuels misconceptions. Improper design can be resolved through the provision of standards and specifications. 3. Lack of scientific data occurs because insufficient record-keeping and performance monitoring is carried out. Lack of scientific data prevents the costs and benefits of green roofs from being quantified and green roof technology from being adopted. Lack of scientific data can be resolved through design and construction cost tracking, life cycle cost analysis, cost benefit analysis, performance monitoring and research. 4. Lack of market acceptance occurs because green roofs are different and people are typically resistant to change. Lack of market acceptance is resolved through education and where appropriate regulatory and financial incentives. Ultimately, lack of market acceptance is resolved through market transformation.
3.2
A BAD REPUTATION FROM THE PAST Today’s green roofs are not the same as roof gardens built in the 1970s or 1980s. Most earlier green roof applications were on underground parkades with a greater focus on aesthetics than on technical performance. For example, little attention was paid to installing roof membranes that were resistant to root penetration. In Germany: ...the major factor contributing to the public’s impression that green roofs can be problematic was the failure of many green roofs installed during the initial green roof construction boom. New, inexperienced companies simply made mistakes or installed poor quality, cheaper materials and ‘cut corners’ in order to keep costs down. This form of negative advertising adversely affected the entire industry.” (Herman, 2003)
As described in section 2, today’s green roofs are engineered systems designed for long term, low maintenance performance.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Modern waterproof membranes are highly sophisticated and provide superior performance. Some of these same membranes are used as liners in reservoirs and other hydraulic structures. Major suppliers in conjunction with approved roofing contractors offer 10 to 15 year warranties on their green roof products.
Green roofs protect the waterproofing membrane from UV, temperature and physical damage, such that green roofs typically do not need ongoing membrane patching or repairs, and furthermore, have a life of 40 years, compared to 20 years for a conventional system.
New membrane leak detection technologies are reducing the risk associated with leaks in both green and conventional technologies.
Solution: Standards, specifications, warranty, reputable manufacturer with long history and an approved roofing contractor.
3.3
GREEN ROOF MISPERCEPTION WITH ENVELOPE FAILURES The perception of green roofs in Metro Vancouver is often clouded by association with the large scale building envelope failures that began to manifest in the region in the early 1990s. Kim Davis (2002) writes that: Many of the concerns and assumptions about landscaped roofs appear to stem from the atmosphere created by the region’s leaky condo situation, and a lack of understanding of contemporary green roof design and construction. One landscape architect noted that these concerns dramatically increase when the landscaping is over habitat space.
“Leaky condo syndrome” is defined as catastrophic failure of the building envelope allowing water to enter the envelope and leading to rot, rust, decay and mould.66 The syndrome has affected condominiums, detached homes, schools and hospitals. Leaky condo syndrome affects buildings constructed in the early to mid 1980s when the Lower Mainland experienced a dramatic increase in housing construction and a similarly dramatic increase in land prices.67 A number of factors, including a shift to a southwest U.S. architectural style, a change in municipal building bylaws for calculating floor area and an erosion of good construction practice and dilution of trade skills as the demand for labour outstripped the supply in the booming market, led to the construction of buildings with envelopes incapable of blocking the ingress of rainwater.
66
URL: http://www.cmhc.ca/publications/en/rh-pr/tech/03-108-e.html
67
URL: http://alcor.concordia.ca/~raojw/crd/essay/essay000347.html
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
The major factor causing the exterior water penetration problem in leaky condos was exposure, both in terms of orientation with respect to weather and problems with or lack of overhangs above walls.68 Ninety percent of the problems were associated with interface details such as windows, balcony and exterior walkway connections, penetration through the walls for wiring or vents, or where elements such as handrails penetrated the cladding to connect to the structure. The leaky condo syndrome is not related to roofing systems, whether green or conventional. As Maureen Connelly, Research Program Head at the BCIT Centre for the Advancement of Green Roof Technology, said: “Nothing about a green roof will make a building leak. Poor detailing of any roof will cause a problem. A properly detailed roof is a key factor – it’s not whether it’s green or not”.69 In Germany, Herman70 credits the FLL guidelines for “reversing the downward spiralling reputation of green roofs.” The FLL – Research Society for Landscape Development and Landscape Construction – is the governing body which issues guidelines for green roof installation practices in Germany. Solution: Guidelines, standards, specifications, public education.
3.4
REPAIRS Repairs are more difficult and potentially more costly on a green roof than a conventional roof and leaks may or may not be more difficult to find. However, the need for repairs generally arises from faulty workmanship, faulty design, lack of or incorrect maintenance and rarely from material failure. Addressing those issues through appropriate expertise in design and maintenance should make green roofs less likely to leak than conventional roofs. New technologies have been developed over the past several years to troubleshoot green roof leaks. Previously, a large amount of growing medium would have to be removed to expose the membrane. Locating the leak and repairing it was not an exact science, but is similar to repairing any conventional membrane leak. The additional repair cost for green roofs is displacing the growing medium over a distributed area to prevent concentrating the loading. Today, however, companies including International Leak Detection, Detec Systems, and Levelton specialize in using leak detection equipment that can pinpoint the leak on either a green or conventional roof to within centimetres71 through Electric Field Vector Mapping (EFVM). Modular or mat green roof systems offer greater ease of repair, should it be necessary.
68
http://www.morrisonhershfield.com/papers/F8DBM55.pdf
69
Mah, 2004
70
Herman, 2003
71
International Leak Detection, Pers Com. April 2005.
3-3
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Aside from leaks, the replacement of the roofing membrane at the end of its lifespan may also be a concern. If a green roof is installed on a high-rise building, there would be no easy way to shift the green roof materials off of and then back on to the roof in order to replace the roofing membrane. There could be several approaches that would allow replacement of the roof membrane on a high-rise building, including: overdesign of the structure to allow shifting of the materials to one side as the membrane is replaced in sections; or use of a tray-type installation that would allow the separate segments of green roof to be removed and replaced manually via the roof access points. Solution: Technology, public education.
3.5
MAINTENANCE Proper maintenance can also prevent future leaks. For example, it is important to remove tree seedlings and other plants whose roots may puncture the waterproof membrane. Drainage needs to be checked and cleared, weeds need to be removed and plants need to be growing well and covering the entire surface. FLL and the British Columbia Landscape and Nursery Association (BCLNA) offer maintenance guidelines for green roofs, and green roof manufacturers have maintenance guides for their particular systems. BCIT covers maintenance issues in its green roof instruction course. Solution: Guidelines for maintenance, public education.
3.6
STRUCTURAL ISSUES Structural load, in particular with wood frame buildings or light steel truss warehouse (which are the majority of buildings in commercial and industrial applications), will be an issue in most instances. This is directly related to the saturated weight of the green roof, which is generally proportional to the thickness of the growing medium. Notably, North American building codes generally permit lower weight bearing capacities than German construction. It is important to involve green roof designers right from the start of the project and to educate engineers to the concepts and design needs of green roofs so that the design can take account of the additional load. For example, on a concrete structure, the increased cost of a 150 mm green roof is almost negligible provided it was incorporated in to the project at the beginning. Costs for wood and steel structures are slightly more expensive, but can also be reduced if incorporated early in the design process. See section 5 for more details on the incremental structural costs.
3-4
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Solution: Incorporate green roof loadings in to the design at an early stage, educate structural engineers and architects on standard loadings and installation details.
3.7
AVAILABILITY OF EXPERTISE Davis (2002) noted that an apparent scarcity of local expertise – knowledgeable and experienced green roof professionals, particularly with extensive systems, was a challenge to green roof implementation. Lack of experience with growing media and plants were included in this limited local expertise. Poor technical support, both in written documentation and customer support, from suppliers was also cited as a problem. Under-bidding, possibly due in part to this knowledge gap, was also cited as a factor in project management and financial difficulties and failures. Solution: Education. As with any new idea, change takes time. However, it should be noted that the green roof manufacturers are well established in Europe and have a significant technical presence in North America. As awareness and interest increase, research and education are also expanding. BCIT, for example, offers green roofs courses and holds monthly open houses to educate the public about green roofs. Green Roofs for Healthy Cities has developed training courses for a Green Roof Professional certification program that will be launched in the spring of 2009.72
3.8
SCIENTIFIC RESEARCH Much of the development of green roof technology comes from Europe, especially Germany. Significant effort has been invested there in system design, substrate formulation, plant selection and maintenance to ensure long term success of green roof applications. However, the majority of German green roof information is published in popular or semi-technical publications and very little in peer-reviewed, scientific journals.73 Furthermore, most of the information that is available from German institutes and universities is published in German, making accessibility difficult by the English speaking community. Over the past ten years, green roofs are gaining popularity in North America because of the multiple benefits they offer to the urban areas. Government and universities have conducted research on this technology to evaluate its suitability and benefits to North America. Since the performance of green roofs and thus their benefits are sensitive to the climatic conditions, green roof research studies are initiated in different climate zones to evaluate specific benefits of green roofs in different regions.
72
URL: www.greenroofs.org for information on developments in this training and certification program.
73
Beattie, 2004; p. 108
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
RESEARCH IN CANADA Research studies have been initiated in Canada to evaluate suitability and quantify benefits of green roof technology in northern climates. The studies are being conducted in major cities as the benefits of green roofs are best realized in an urban context. Major research projects and findings relevant to BC are summarized below: a. Vancouver Public Library’s green roof The green roof on Vancouver Public Library was monitored by Kerr Wood Leidal Associates Ltd. and Public Works Government Services Canada as part of the effort to gain information on Best Management Practices and Low Impact Development methods.74 The objective of the study was to assess the performance of the green roof during rainy and dry seasons. The green roof consisted of mature vegetation growing on 350 mm of growing medium. The piping was modified to include two water meters of different capacities to cover a wide range of flow rates. During the summer when the roof is dry and rainfall events are small, peak flow reduction in excess of 80% was achieved. During the winter when the roof is wet and rainfall duration is long, peak flow reduction was about 30% during smaller events to less than 5% for larger events. The green roof reduced the runoff volume by 16% from July 2003 to February 2004 when compared to that estimated for a traditional flat roof. b. British Columbia Institute of Technology’s Centre for the Advancement of Green Roof Technology75 The British Columbia Institute of Technology (BCIT) constructed a Green Roof Research Facility at its Great Northern Way campus in Vancouver, British Columbia in 2003. The main objectives of Phase 1 of the study were to collect regional data for green roof performance in BC and to educate the public about the benefits of green roofs.76 The BCIT facility was modelled after the Field Roofing Facility at the National Research Council in Ottawa, Ontario. The 90 m2 roof was divided into 3 equal sections by parapets – one section was a reference roof (without green roof) in the middle with two green roof sections on east and west sides. The roof was fitted with thermocouples and heat flux transducers to measure energy efficiency. Each roof section was sloped at 2% towards a central drain where the runoff was collected and measured by a modified tipping bucket flow meter. A weather station was installed on the rooftop to measure local weather conditions. All instruments were connected to a data acquisition system for continuous monitoring. Phase 1 of the study compared the performance of two extensive green roof configurations to the reference roof. The first green roof system (GR-1) consisted of a 74
Johnston, 2004
75
URL: http://commons.bcit.ca/greenroof/
76
Connelly, 2005
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sedum mixture growing in 75 mm of growing medium while the second system (GR-2) was composed of a grass mixture growing in 150 mm of the same growing medium. Both systems contained the same non-reservoir drainage layer and geo-textile filter cloth. Regular irrigation was provided for one full year to achieve good vegetation coverage on the green roofs. Performance monitoring was conducted in 2005. The runoff data showed that the green roofs retarded runoff, reduced peak flow and volume.77 The retention efficiency depended more on the climatic conditions than on the green roof configurations. Vancouver is characterized by hot dry summer and cool wet winter. Out of the 1,508 mm of rainfall recorded during the monitoring period in 2005, only 242 mm fell between mid-April to end of September with the rest of 1,266 mm fell in the fall/winter. Between April and September, GR-2 (94%) retained slightly more than rain than GR-1 (86%). Because of the high temperature and low rainfall during this period, the deeper growing medium in GR-2 offered a higher capacity to absorb rain water, especially during heavier events. During the period between October and March where the temperature was cool and it rained almost every day, GR-1 (18%) retained more rain than GR-2 (13%). These observations corroborated those obtained at the Vancouver Public Library78 and supported the observations made in Seattle,79 where the deepest (20-cm) growing medium did not evaporate moisture as well as the shallower medium depths in the cool wet environment during the winter in Pacific Northwest. The total annual retention was similar for the two green roofs – 29% for GR-1 and 26% for GR-2. The findings indicate that thicker is not always better for growing medium in designing green roofs for stormwater management in the Pacific Northwest where the temperature is cool and the humidity is high, resulting in low evapotranspiration rates for the green roofs during the rainy season. The data from the study also showed that both green roofs were effective in reducing heat flow through the roof throughout the year, therefore saving energy used for space conditioning in the building. The effectiveness was higher (83-85%) in spring/summer than in the fall/winter (40-44%), with an overall annual reduction of 66%. Despite the difference in growing medium depth and plant species between the two roof sections, the thermal performance of the green roofs was very similar, except during the hottest periods of July and August when GR-2 outperformed GR-1 because of the deeper growing medium (thus higher thermal mass). The findings suggested that for the temperate climate of Vancouver, a green roof with shallow growing medium (e.g. 75 mm) can be nearly as effective for thermal performance as one with deeper growing medium (e.g. 150 mm). The green roofs also reduced the maximum temperature experienced by the roof membrane in spring/summer from 50ºC to 30ºC, thus lowering the heat aging on the roof
77
Connelly, 2006
78
Johnston, 2004
79
Gangnes, 2007
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
membrane. Also, the green roofs reduced the median daily temperature fluctuation in spring/summer from 48ºC to less than 5ºC, therefore lowering the thermal stresses experienced by the roof membrane. There was little difference between GR-1 and GR-2. The results suggested that green roofs can increase durability of the roof membrane and extend its service life. Phase 1 of the BCIT study showed that a green roof system with appropriate plant species in 75 mm of growing medium can provide a similar level of stormwater mitigation and thermal benefits as one with 150 mm of substrate. The results suggested that Vancouver can benefit from green roofs with lightweight green roofs with shallow growing medium. This is an important finding since shallower green roof systems mean lower cost on materials and structural upgrade, making green roofs more affordable, particularly in retrofits where upgrade in structure can be prohibitively expensive. It was questionable whether the deeper rooting grasses in GR-2 might have changed the drainage channel structure in the growing medium, thus affecting its water retention capacity as compared to the shallower rooting sedums in GR-1. To eliminate this variable, starting in spring 2006, Phase 2 of the study at BCIT’s Green Roof Research Facility compared two green roofs with the same sedum mixtures growing on two different depths of the same growing medium (75 mm and 125 mm). In addition, Phase 2 of the study also examined the effectiveness of using sedum cuttings as an economical propagation method for green roof applications in Vancouver. c. Regional Infrastructure Network in BC BCIT’s Centre for Architectural Ecology created a Regional Infrastructure Network (RIN) to support the evaluation of green roofs as a sustainable approach for future development in the Metro Vancouver region. This network includes the green roofs on the Electronic Arts building in Burnaby and the Operations Building in White Rock. Electronic Arts’ Motion Capture (MOCAP) building has a 1760 m2 extensive green roof. BCIT outfitted it in 2006 with thermocouples and flow meters for performance monitoring. The study aims to evaluate the stormwater management potential and study its implication on the energy efficiency of the building. The White Rock Operations Building has a 135 m2 extensive green roof. In 2007, BCIT modified the piping and installed flow meters to record the runoff from the green roof. The study aims to evaluate the effectiveness of the green roof as a stormwater source control tool. BCIT will also determine various hydrological parameters of the growing medium that affect the water retention capacity of the green roof. d. Roof Evaluation Modules at BCIT80
80
URL: http://commons.bcit.ca/greenroof/testing.html
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
The Roof Evaluation Module (REM) is an innovative tool that allows researchers to evaluate and compare the engineering performance of green roof systems through field monitoring. Each REM resembles a mini-building with an experimental roof deck over a temperature-controlled interior space. The roofing and green roof systems are fully set up to measure the temperature profile, heat flow and roof runoff. REMs enable manufacturers and researchers to change the variables and configurations of green roof systems and evaluate the effects systematically. In collaboration with various roofing and green roof manufacturers, BCIT is collecting performance data from ten REM’s consisting of different green roof system designs. The results will not only provide information on performance of individual green roof systems, they will also assist the researchers to better design green roof systems for the Pacific Northwest. e. National Research Council’s Institute for Research in Construction’s green roof research program.81 The National Research Council’s Institute for Research in Construction established the first field facility dedicated for green roof research in Canada – the Field Roofing Facility – at its Montreal Road campus in Ottawa, Ontario in 2000. The objectives of the study were to quantify the energy efficiency and stormwater retention potential of the green roof and examine the applicability of green roofs in northern climates such as Canada.82 The 70 m2 rooftop was divided into two equal roof sections by a median parapet – one with and one without a green roof. The indoor environment of the facility was kept to a constant temperature via thermostat. The roof was fully wired with thermocouples and heat flux transducers to measure the temperature profile and heat flow across the roofing systems. Each roof section was sloped at 2% to a centre drain where the roof runoff is collected and measured by a tipping bucket flow meter. Two weather stations, one on the rooftop and one about 100 m from the test building, recorded the local weather conditions. All instruments were connected to an automatic data acquisition system for continuous monitoring. Findings from the Field Roofing Facility showed that the green roof with grasses planted on 150 mm of lightweight growing medium increased the energy efficiency of the roofing system.83 The green roof was particularly effective in reducing heat entry in the summer through shading, insulation, evapotranspiration and thermal mass. It reduced over 85% of heat flow through the roof in the summer when compared to the reference roof (without a green roof). The thermal efficiency was overshadowed by the deep snow coverage (e.g. over 200 mm) in the winter, which provides good insulation to both roof sections. The heat flow reduction averaged at about 15% when compared to the reference roof. In addition, the green roof was effective in mitigating stormwater runoff from the roof by retarding runoff, lowering the peak flow and total runoff volume. The
81
URL: http://irc.nrc-cnrc.gc.ca/bes/index_e.html
82
Liu, 2003
83
Liu, 2004
1
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
green roof retained 54% of the annual rainfall that would otherwise go into the stormwater infrastructure. In addition, the extensive green roof lowered the maximum roof membrane temperature by over 30ºC in the summer and reduced the median daily temperature fluctuation experienced by the roof membrane from 45ºC to less than 6ºC. These temperature data suggested that the green roof can extend the durability of the roof membrane by reducing heat aging and thermal stresses. The grasses also survived on the roof over the winter and without supplementary irrigation in the summer on 150 mm of growing medium. This study demonstrated that extensive green roofs have the potential to benefit buildings in urban areas from an engineering perspective. f. City of Toronto Green Roof Research and Demonstration Program This was a collaborative effort between the City of Toronto, the National Research Council’s Institute for Research in Construction, Environment Canada, Green Roofs for Healthy Cities and the Climate Change Action Fund.84 The objectives were to develop green roof research and demonstration sites in the City of Toronto to quantify the benefits of green roofs in Toronto’s specific climate zone and to increase public awareness of the benefits of green roofs. The City of Toronto established extensive green roofs on the Toronto City Hall and the Eastview Neighbourhood Community Centre. The Toronto City Hall project consisted of eight green roof plots of various themes such as a butterfly garden, urban agriculture and native plants. Four of the green roof plots were monitored for thermal performance by the National Research Council.85 Since this is a protected roofing membrane assembly (i.e. inverted roof), the green roof lowered the membrane temperature only slightly due to the presence of extruded polystyrene insulation shielding the roof membrane from temperature changes. However, the extensive green roofs were shown to reduce the heat flow through the roof by over 8090% in the summer and 10-30% in the winter, thus potentially reducing the energy demand for air conditioning. The Eastview Neighbourhood Community Centre consisted of about 450 m2 of green roof over its gymnasium. Two commercial green roof systems were evaluated – one with 75 mm of substrate and the other with 100 mm of a different substrate. Small plant plugs were grown on both green roofs with about 20% of initial vegetation coverage. Both green roofs effectively reduced heat flow through the roof, more in the summer (70-90%) and less in the winter (10-30%).86 Both green roofs also reduced the runoff from the roof, averaging 56% reduction in annual runoff and 10% to 30% reduction in peak flows. This study demonstrated that extensive green roofs are effective in reducing energy demand for cooling and effective in stormwater management for the City of Toronto.
84
Gutteridge, 2003
85
Liu, 2004
86
Liu, 2005
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
g. York University Green Roof The green roof study was initiated by the Toronto Regional Conservation Authority in 2002 to examine the stormwater management and biodiversity benefits of green roof technology in cold climates.87 The monitoring study was conducted on a green roof sloped at 10% on York University Computer Science and Engineering building. Two roof surfaces, a green roof and a control roof were instrumented with flow meters and soil moisture sensors. The runoff retention was 54% in 2003 and 75% in 2004. The lower retention in 2003 was due to greater precipitation in the fall in that year. The retention rates were better in the summer (78-85%) than in spring and fall (39-64%), likely due to higher temperature and evapotranspiration rate in the summer months. Retention rates varied due to rainfall intensity and rainfall volumes, evapotranspiration and antecedent moisture contents. Water quality analysis was conducted on 21 storm events during the two-year monitoring period.88 The study showed that the total loads for most pollutants of concerns were lower from the green roof than from the control roof. Part of the reason was due to the smaller runoff volumes from the green roof. The green roof had higher loads of potassium, magnesium, calcium and phosphorus, which formed part of the growing medium. Phosphorus is of particular concern since elevated concentration in rivers and lakes can adversely affect aquatic organisms. It was noted that phosphorus concentration dropped over the monitoring period, likely due to continuous leaching out of the soil over time. RESEARCH IN UNITED STATES Several universities, government departments and engineering firms have conducted green roof research in different parts of USA. Some of the major green roof research centres and projects are highlighted below. These projects generated fundamental understanding in substrate formulation and system design that help to advance green roof technology in North America. Performance monitoring projects that are conducted in Portland, Oregon and Seattle, Washington are of particular relevance to BC because of the similarity in west coast climate pattern. a. Michigan State University89 The green roof research program at MSU was initiated in collaboration with Ford Motor Company during 2000 in an effort to evaluate different options for the installation of a 4.2 hectare extensive green roof on a truck assembly plant in Dearborn, Michigan. The objectives of MSU’s green roof research program are to evaluate plant species, 87
MacMillan, 2004
88
MacMillan, 2006
89
URL: http://www.hrt.msu.edu/greenroof/
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
propagation and establishment methods, plant succession, carbon sequestration potential, water and nutrient requirements, water quality and quantity of stormwater runoff and energy consumption. Field experiments are currently being conducted on the roofs of two buildings on campus, in green houses and on a series of roof test platforms. The roof of one of the test buildings is equipped with temperature and heat flux sensors to measure the temperature profile across the various layers of the roof, as well as at various depths of the growing substrate and indoor and outdoor air temperatures. In addition, runoff from individual test platforms is monitored by electronic tipping buckets to evaluate the runoff retention efficiency of various green roof configurations. Long-term plant survival, persistence and succession are also being studied with different system and site parameters. b. Penn State University’s Centre for Green Roof Research90 The centre is a partnership between faculties from Horticulture, Agricultural and Biological Engineering, the Department of Architectural Engineering at Penn State, University Park, and The Environmental Pollution Control Program at Penn State, in Harrisburg, Pennsylvania. The mission of the Centre is to characterize and quantify the performance of green roofs and to promote their use through education and outreach. The centre uses small test green roofs on replicated buildings for research purpose. Research studies included storm water runoff quality and quantity, building energy consumption and insulation value, chemical and physical characteristics of growing media, plant selection, plant water use, waterproofing resistance to root penetration and drainage materials for green roofs. The centre also performs testing of green roof media and waterproofing materials using FLL and ASTM methods. c. The University of Texas at Austin, Lady Bird Johnson Wildflower Centre, Green Roof Research Program91 This research program is a partnership between the University of Texas at Austin and the roofing and green roof industry. The objectives of the research program are to examine the performance of green roofs in Texas and the use of native plants for green roof applications. The study involves a series of roof test platforms, each of which is outfitted with instruments including temperature sensors to measure the temperature profile across the green roof assemblies and a flow meter to measure the runoff from the green roof. Various green roof assemblies with different parameters such as substrate types and depths and plant types are being studied. Native plants are grown on the modules to examine their survival and success rates on green roof applications.
90
URL: http://web.me.com/rdberghage/Centerforgreenroof/Home.html
91
URL: http://www.wildflower.org/greenroof/
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
d. North Carolina State University’s Biological and Agricultural Engineering Green Roof Research92 North Carolina State University currently has two extensive green roof research sites: Wayne Community College in Goldsboro, NC and the Neuseway Nature Centre in Kinston, NC. The main objectives of the research program are to evaluate the quantity and quality of stormwater runoff and plant growth. There is a control roof and an undisturbed rooftop on each site to provide comparison for runoff. Flow rate and volume of runoff are measured by weir boxes while automatic samplers collect water samples for quality analysis. Different types of succulent plants such as sedums and delosperma are used in the studies. e. Portland Oregon The Bureau of Environmental Services of the City of Portland monitored several ecoroofs, or green roofs, to quantify their potential in stormwater management. Two of the ecoroofs studied are the Hamilton Apartment Ecoroof and the Multnomah County Building Green Roof. The Hamilton Apartment Ecoroof also featured two green roof types – a thinner, lighter substrate on the east side and a thicker, heavier substrate in the west side. The results showed that all roof configurations worked well in reducing peak flow and therefore would help reduced incidence of flash flooding during heavy storms.93 Volume retention at the Hamilton Apartment Ecoroof varied with season – higher retention was observed in the summer (67-86%) when rainfall is low and evapotranspiration rates are high. In comparison, lower retention (14-47%) was recorded in the winter due to high rainfall and low evapotranspiration rates. The high retention in the summer was important because regulations for water quality and combined sewer overflows are most stringent during these months. Hamilton West showed higher annual retention (56%) than Hamilton East (27%). The differences appeared to derive mainly from the difference in soil media. Hamilton West contained a substantial amount of fine particles (sandy loam) in the soil, allowing it to hold water longer for evapotranspiration to occur and for other components in the soil to absorb water. Also, it was possible that the fine particles may partially clog the filter fabric and keep the water out of the drainage system. It is interesting to note that the annual and seasonal retention for the Hamilton Apartment Ecoroof improved over each of the four years of monitoring. The annual runoff retention of Hamilton West increased from 41% in 2002 to 63% in 2005 while that of Hamilton East increased from 4% in 2002 to 55% in 2005. The researchers suggested that retention performance of ecoroofs improve as the soil and plant complex mature.
92
URL: http://www.bae.ncsu.edu/greenroofs/
93
Adams, 2006
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
The water quality analysis of the roof runoff showed that metal (copper and zinc) and nutrient (phosphorus) concentration in ecoroof runoff were at levels that could impact watershed health. The levels of zinc and copper appeared to be rising over the four years of monitoring. While the soil contained zinc and copper, the corrosion of roofing materials such as flashing and railings might be a factor. The results also showed that phosphorus appear to decrease over time, possibly due to leaching from the growing medium over time. However, the levels were still high (0.35mg/L) when compared to benchmarks established in some Portland watersheds (0.13-0.16mg/L). The City of Portland also published a study evaluating the costs and benefits of a green roof over the life of the roof, separating the benefits into private and public to differentiate who receives the benefit. Private benefits accrue to the owner of the property over time, such as energy savings on cooling and heating, while public benefits accrue to the public over time, such as heat island mitigation and carbon sequestration. The study found that at the 5-year mark there was a net private cost of a 3716 m2 roof, but over the 40-year expected lifespan of the roof the study estimated a net public benefit of $404,000 and a net private benefit of $191,421.94 f. Seattle Green Roof Evaluation Project (GREP) Magnusson Klemencic Associates initiated the GREP to monitor runoff characteristics of five green roof test plots in downtown Seattle in 2005.95 The 2-year project aimed to evaluate the effectiveness of green roofs as a low impact development (LID) tool to manage stormwater in the urban areas.96 The five test plots varied in drainage layer, substrate types and depths, and vegetation types and coverage to provide different system configurations for comparison. Flow meters were installed on each test plot to measure runoff.97 Data were collected for 18 months. Cumulative measurable runoff mitigation ranged from 65% to 94%. The data showed that the green roofs were effective in reducing runoff even in Seattle’s wet climate in winter.98 For the green roof test plots with substrate between 50 – 150 mm thick, the soil moisture data showed that they were able to dispose of 12 mm of rainfall in just 2 days. However, the test plot with 200 mm thick substrate remained relative moist over the same period. The researchers suggested that 200 mm was too thick to allow evaporation to occur as readily as the thinner plots. The report further suggested that the optimal green roof thickness would be between 100 mm and 150 mm for stormwater management in Seattle.
94
David Evans and Associates, Inc., 2008.
95
Gangnes, 2006 and Taylor, 2005
96
Gagnes, 2006
97
Taylor, 2006
98
Ganges, 2007
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Solution: Scientific research is being conducted in North America to provide information on various aspects of green roof performance. Much of the fundamental research on substrate and materials are universal and can be adopted or adapted for BC. However, because of the unique climate of BC, performance data from eastern and central Canada may not be relevant and data from Pacific Northwest such as Portland, Seattle and Vancouver are necessary for green roof design in BC. Designers are therefore encouraged to use data coming from research projects in these regions. More local scientific research will better address region-specific issues in BC.
3.9
FEAR OF THE UNKNOWN/“FIRST TO MARKET” RISK Lack of information leads to narrow perceptions and “fear of the unknown” on the part of developers/builders as well as regulators. Reluctance on the part of local governments to approve ‘new things’ is legendary, as is the reluctance of builders to be ‘first’ to try something new. This applies more to the multi-family residential buildings rather than the commercial and industrial buildings as the latter tend to focus more on life-cycle costs rather than public perception. One solution is to expand the scope of the Certified Building Envelope Specialist designation. Certification of a green roof by an expert would draw the liability away from the regular builder or municipal inspector. Another solution is to provide added incentives to put green roofs on private, multifamily residential buildings. The incentives could be temporary until the first few buildings are built. Incentives could include “density bonuses” which eliminate the need for money to change hands. Further, land owned by a municipality that is to be sold to the private sector is also a perfect candidate to initiate green roof development on multifamily rooftops. The Southeast False Creek Lands represent a golden opportunity to achieve these firsts. Solution: Champion developers, an expanded Certified Building Envelope Specialist designation and incentives.
3.10 COST Davis99 notes in her inventory of green roofs in Metro Vancouver that the cost of a green roof was by far the largest deterrent for many clients of landscape architects and architects. Even where green roofs are part of the building design, when cost cutting is required, the green roof is usually one of the first elements to be eliminated.
99
Davis, 2004; p. 14
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Compared to Germany where installation costs for green roofs are about $40/m2, installation costs in North America range from $80 to $200/m2 – about double that of a conventional roof.100 Reasons for these higher costs include a comparative lack of economies of scale, lack of companies in North America that can do an entire installation (unlike Germany, where specialist companies do the entire installation under a single contract), and a relative lack of materials and supplies specific to green roofs in North America compared to Germany. When examining costs, however, it is important to separate intensive green roofs from extensive green roofs. Intensive green roofs are far more expensive per unit area than extensive green roofs. Also, any cost analysis should attempt to take into account the full life-cycle costs101 (e.g., extended life span of the membrane resulting from green roof protection) and benefits that cannot be readily quantified (e.g., biodiversity and improved interior heat management). It should be noted that while construction costs for green roofs are significant, there has not been significant evidence of on-going costs associated with green roofs for maintenance or repairs due to leaks or problems with properly installed systems. Nonetheless, offsetting costs is one of the reasons why many parts of Germany provide direct and indirect financial incentives such as subsidization programs and reduced stormwater fees. Any government trying to promote green roofs should look carefully at the legislative and policy measures that are being employed. Solution: Municipalities may consider implementing financial mechanisms to offset the costs of green roof construction with their reduced off-site costs (see sections 4 and 5).
3.11 LACK OF STANDARDS Neither B.C. nor Canada has detailed design guidelines, standards that are integrated into the building code, or a procedure for testing materials and new products. “Without regionally relevant research and concise design standards and guidelines, many professionals will continue to perceive green roofs as ‘new’, untested and hence, risky”.102 The FLL’s document Guidelines for the Planning, Execution and Upkeep of Green Roof Sites has been the standard resource for green roofs for many years. Happily, the latest
100
Beattie, 2004 and TRCA, 2007
101
Green Roofs for Healthy Cities (GRHC) has an online green roofing cost calculation tool called “Greensave Calculator”, developed by GRHC and the Athena Institute. The tool compares roofing alternatives over a specific time period to determine which has lower life-cycle costs. URL: http://www.greenroofs.org/index.php?option=com_content&task=view&id=626&Itemid=116
102
Davis, 2002: 15
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
2002 edition is now available in English.103 “The German FLL guidelines provide a source of information for the interim, but they should be evaluated for their application to local building practices and climates in Canada”.104 Additional standards for green roofs are being and have been developed. The British Columbia Landscape and Nursery Association (BCLNA) has developed a “BC Standard for Extensive Green Roofs” in conjunction with the British Columbia Society of Landscape Architects (BCSLA). This publication defines standards for green roof components from the membrane up. FM Global, an insurance industry group, has a general guide on green roof systems “Green Roof Systems (Property Loss Prevention Data Sheet 1-35)” that covers design and maintenance concerns of green roofs. A proposed ASTM International standard, WK14283, “Guide for Green Roof Systems”, will identify terminology, principles and concepts related to the construction of vegetated green roof systems. The proposed standard is being developed by Subcommittee E06.71 on Sustainability, part of ASTM International Committee E06 on Performance of Buildings. ASTM is also developing a new work practice which is currently designated ASTM WK575 – “New Practice for Assessment of Green Roofs”, but which is considered to be a much longer range project than WK14283. ASTM WK14283 is expected to provide initial guidance and a significant source of information for green roofs in the interim. Solution: Standards, flood testing, leak detection systems.
3.12 INSURANCE COVERAGE In May 2007 the Green Roofs and Homeowner Protection in British Columbia conference was hosted by the HPO to formulate recommendations to the Homeowner Protection Office (HPO) Board of Directors about insuring buildings with green roofs. Before green roofing technology becomes widely insurable, it must be shown that no additional cost or risk will be created for homeowners on a long-term basis as a result of the installation and maintenance of green roofs. HPO’s primary concern was the possible conflict between local government mandates for green roofs and the fulfillment of the consumer protection requirements of the Homeowner Protection Act, specifically that insurance is mandatory. Of the four home warranty insurance providers active in the province, only one at that time was prepared to consider providing home warranty insurance for residential projects with green roofs and then only in very specific circumstances. The HPO report makes it clear that, “it is technically feasible to design, install and maintain a green roof such that it performs as well as a conventional roof or
103
http://www.f-l-l.de/artikel_3187.html
104
Ngan, 2004
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
better.” The insurance issues surrounding green roofs centre on the cost-benefit value of green roofs, the probability that such roofs will be designed, installed and maintained properly and the risks that may arise if they are not.105 The risks that may arise from failure to design, install and maintain green roofs properly were defined as: •
The failure of the membrane or other related roof component or detail, leading to water penetration and damage to residential units;
•
The destruction of the plant material through drought or other influence, leading to the failure of the roof to perform as intended;
•
Economic losses for homeowners if failures occur that are not covered by home warranty insurance and/or property and casualty insurance; and
•
Significant losses for home warranty insurance providers if green roof failures are widespread.
In May, 2007, the HPO committee could not state that there was an extensive body of experience and expertise in green roofing within the various climatic zones in British Columbia. They could also not state that, in addition to cost benefits, there was a sufficiently low probability of risk and actual risk to recommend the implementation of green roofing technology in the residential sector. The HPO suggested that at the present time, the primary focus of experience with green roof technology in British Columbia should continue to be in the industrial, commercial and institutional sector, where buildings typically have a single owner with expertise, more involvement in the design and construction phases and the incentive to take a longterm view of the application of new technologies. In BC’s commercial building sector, there have not been the same insurance issues. Concerns around liability and risks can be reduced by requiring that all green roof installations are to be signed-off or certified by a professional as is already required for standard roofs on commercial and industrial buildings in most jurisdictions. The professional’s liability insurance then provides financial protection in the case of failure. Close attention should be paid, however, to the terms of the insurance policies that cover the work of these professionals, as the insurance industry has begun to exclude water penetration claims from errors and omissions insurance coverage for design professionals.106 Recent conversations with several insurance company personnel in 2009 indicate that progress is being made on the insurance issue. Several high profile projects in the Metro
105
HPO, 2007
106
HPO, 2007
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Vancouver region are under construction with full insurance coverage, including the Millennium Water project which will be the first major residential construction to include green roofs. While some insurance companies express concerns, others are moving forward with green roof projects in the understanding that green roofs that are well designed and well constructed will perform as designed and do not pose an increased risk for the insurer. Solution: More research on risk and reliability in green roof installations in the region and continued communication between the design, engineering, construction and insurance industries as data and technologies improve.
3.13 FIRE HAZARD AND UPLIFT Research in this area is sparse. However, with the appropriate plant mix, green roofs appear to be less of a fire hazard than tar or gravel roofs. Sedums and other succulents are fire resistant whereas long, dry grasses may pose a fire hazard. Fire breaks further reduce risk. There is also some risk of wind damage due to uplift of the green roof structure. Solution: More research on wind uplift and use of fire breaks and fire resistant grasses.
3.14 ARCHITECTURAL STYLE A significant barrier to wide spread green roof acceptance is changing the architectural style of certain land uses. It is unlikely that in the foreseeable future green roof advocates will be able to persuade the public to flatten single-family residential roofs, which are generally 30- to 45-degree angle for aesthetic reasons, in order to install green roof systems. However, it may be possible to promote the use of green roofs on land uses and building styles already having flat rooftops. These land uses include multi-family, commercial, institutional and industrial land uses. Land-use data from 2000 was used to estimate the percent coverage of various land-uses in the City of Vancouver. Based on the type of land-use, it may be assumed that a certain percentage of those roofs are flat or nearly flat and combining the percentages gives an estimate of how much of the existing City land area could be adapted for green roof technologies.107 Table 3-1 summarises the percentage of these rooftops throughout the City of Vancouver. Table 3-1: Determination of Potential Green Roof Areas in the City of Vancouver Land Use Total Estimated Possible Potential
107
source: Land Use in the City of Vancouver, Nowlan 2000
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER Area (%)
Roof Top Area (%)
Green Roof Applicability (i.e. flat) (%)
Green Roof Area (%)
Single Family Multi-Family Parks and Open Spaces Institutional Commercial Industrial Streets, Lanes, Sidewalks
32 6 12 6 4 8 32
50 80 0 30 90 30 0
0 70 0 100 100 100 0
0.0 3.4 0.0 1.8 3.6 2.4 0.0
Total
100
11.2
Therefore, it can be concluded that overall, 11.2% of the land mass could be made available for green roofs without significantly changing architectural styles, with the exception of steep roof multi-family. In municipalities outside the City of Vancouver, there are significantly more peaked roof multi-family buildings. Efforts should be made to encourage a flatter style of roof. This percentage will be considerably higher in watersheds that are predominately multi-family and commercial land uses. Solution: Education, incentives, encourages flatter (greened) roof styles.
3.15 AESTHETICS Some argue that extensive green roofs look messy and are not “green”. “The appearance of extensive green roofs should not be compared to lawn and traditional gardens. Extensive green roofs have a natural appearance that changes with the seasons. They are more similar to dry wildflower meadows and develop much in the same way as natural systems. “…. when we can associate how a healthy functioning extensive green roofs looks with the ecological benefits that they afford, then we will have an eye for sustainability”.108 The City of Portland prefers the term “eco-roof” because it emphasizes the ecological functions over the colour green.109 Another more appropriate term could be ‘living roof’, as this reflects the intent of a natural, living system rather than a design for purely aesthetic or human purposes.
108
Ngan, p. 9
109
Hauth and Liptan, 2003
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Solution: Changing public perception, incentives and education.
3.16 INTERVIEWS WITH DEVELOPERS Based on discussions with Metro Vancouver at the beginning of the project, it was felt that the key barriers for green roof implementation were faced by the development community and building owners. Other groups such as municipal staff, architects, engineers, insurance agencies, banks and fire departments also have concerns, but the barriers facing the development community and building owners are more numerous and carry more financial risk. As a result, it was decided to interview a number of individuals and companies that have either considered implementing green roofs or have actually built a green roof to identify what they feel are the major barriers to implementation. Two types of interviews were held with development/building owners group: 1. Informal Discussions: involving a wide range of businesses and individuals through telephone calls. 2. Case Study Discussions: involving a review of the barriers, costs, and benefits of two recently constructed green roofs. Sections 5.6 and 5.7 show two case studies: The Silva building in North Vancouver and the White Rock Operations building in White Rock. The informal discussions involved dozens of individuals. However, many wish to remain anonymous, as they do not want their affiliations to be branded as “anti-green”. KEY CONCERNS RAISED IN INFORMAL DISCUSSIONS Surprisingly, it appears that the concerns about green roofs from the past are not necessarily the concerns today. Previously, the concerns focussed around costs, leaks, insurance and public perception in the aftermath of the leaky condo affair. Green roof costs are still a concern today, but have lessened for concrete construction associated with commercial developments. The greater concern now has become “how do you replace the membrane when the design life is reached?” This is mostly a concern in high rise towers where it would be extremely expensive to remove the growing medium. Replacement of the roof membrane (beneath the green roof) at the end of its useful life is an area of concern for developers which requires more research. It is certainly possible that the growing medium can be moved from one part of the roof to another, but the structural loads would have to be reviewed. Since roof tops are designed to take a considerable snow load, there should be ample opportunity to move the soil around, but it still raises a valid concern.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
HPO GREEN ROOF TASK FORCE REPORT At the Green Roofs and Homeowner Protection in BC conference in May 2007 a survey was also produced to get input from conference attendees on main issues with respect to green roof design and construction on new residential buildings, specifically: home warranty insurance, the role of local governments and maintenance requirements for strata corporations.110 The resulting Green Roof Task Force Report was very cautious towards green roofing technology being used in new residential construction and made these 6 recommendations111 that the HPO Board of Directors should: 1. Advise local governments against mandating extensive green roofs in residential construction at this time. 2. Request home warranty insurance providers to specify the conditions, if any, under which they would accept for initial consideration a request for home warranty insurance coverage for a residential building with a green roof. 3. Review the Homeowner Protection Act to clarify the provision and coverage of mandatory home warranty insurance with respect to extensive green roof installation and maintenance. 4. Recommend to the provincial Office of Housing and Construction Standards that consideration be given to the issues surrounding extensive green roofs in the Green Building Code, including regional climatic variations within the province. 5. Continue to support research and education activities that will expand the knowledge base about the design, installation, maintenance, durability and life expectancy of extensive green roofs in the different climatic zones in British Columbia. 6. Recommend that the Minister of Finance consider the need to ensure that strata corporations’ obligations for maintenance of green roof systems are strengthened in the Strata Property Act.
110
HPO, 2007
111
HPO, 2007
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Section 4
Regulatory Stormwater Control Criteria
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
4. REGULATORY STORMWATER CONTROL CRITERIA 4.1
INTRODUCTION Many of the above categories fall into the “soft cost” area and although the benefits are real and measurable, they are difficult to implement thus difficult to motivate a developer to build green roofs. In the subsections below, the benefits of stormwater runoff mitigation due to a green roof are quantified as estimated cost benefits. The benefit calculations are all based on the “baseline green roof”’ identified in section 2.6. This represents an extensive type green roof with a growing medium depth of 150 mm, as specified below in this chapter. Generally, deeper growing medium depths provide higher stormwater storage capacities. The stormwater effectiveness of green roofs is in direct proportion to the water storage capacity of its growing medium and plants. In the Metro Vancouver climate, growing medium depths may need to approach 300 mm in wetter parts of the region to meet 100% of rainwater capture targets and thus to avoid the need for off-roof or at-grade stormwater source control. However, successful designs using wood/steel lightweight structures will balance a certain amount of on-roof rainwater capture with green roofs with a companion role for at-grade stormwater source control.
4.2
THE STORMWATER BENEFIT By far the greatest measurable benefit for the Lower Mainland, with a high degree of expected implementation success, is the stormwater category. Municipalities already charge costs to developers to deal with the negative consequences of stormwater off-site. Municipalities and senior Provincial and Federal Agencies also demand certain stormwater criteria to be met on-site that can further add to these costs. If these negative consequences could be reliably offset by green roof systems, offsetting credits could be used to establish credits for green roof construction. SALMON HABITAT – CREEK SYSTEMS The reason why stormwater provides the greatest benefit is due to the fact that in Metro Vancouver, we are heavily focussed on the protection of salmon habitat and compliance with the Fisheries Act. It has been proven that increasing impervious area destroys fish habitat. To mitigate this, development must control stormwater quantity and flow rates. The Pacific Northwest has a completely different stormwater business case than many other areas of the world. In order for the stormwater benefits to be truly realized, green roofs constructed in Metro Vancouver, MUST meet the stormwater criteria outlined by
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
either the Department of Fisheries and Oceans’ (DFO) Urban Stormwater Guidelines112 OR Stormwater Planning: a Guide Book for British Columbia113, AND a municipality’s local stormwater control bylaw, OR that prescribed in a local Integrated Stormwater Management Plan (ISMP). Otherwise, municipalities will be required to construct offsite works to mitigate the impact of the impervious surfaces and will be unable to offer offsetting financial benefits. Typical stormwater criteria would likely be comprised of the components listed in Table 4-1 Table 4-1: Typical Stormwater Criteria1 in Metro Vancouver Volume Reduction: 6-month 24-hour post-development volumes from impervious areas are not discharged and are infiltrated to ground. If infiltration is not possible, the rate-of-discharge from volume reduction Best Management Practices (BMPs) will be equal to the calculated release rate of an infiltration system. Water Quality: Collect and treat the volume of the 24-hour precipitation event equalling 90% of the total rainfall from impervious areas with suitable BMPs. Rate of discharge will not be greater than required to provide suitable hydraulic retention time as to maximize the effectiveness of the specific BMP. Flow Rate Control: Post-development flows match the volume, shape and peak instantaneous rates of pre-development flows for the 6-month 24-hour, 2-year 24-hour, 5-year 24-hour, 10-year 24-hour, and 100-year 24-hour precipitation events. 1
A blend of DFO’s Stormwater Criteria for the protection of aquatic habitats and typical municipal criteria to protect against flooding and erosion in downstream conveyance systems
If a green roof can demonstrate that the above criteria are met, it is possible that an offsetting financial credit may be obtained from a local municipality provided a legal framework is in place to offer a credit. REDUCTION IN STORMWATER INFRASTRUCTURE There is also a downstream infrastructure benefit when green roofs are implemented. The benefit can be calculated two ways: 1. Reduced 10-year and 100-year peak flows; and 2. Reduced impact to existing infrastructure due to climate change. The purpose of this section is to quantify the green roof stormwater benefits identified above and develop financial mechanisms allowing builders to realize those benefits. This section relies heavily on research carried out by KWL, Public Works Canada, The City of
112
Urban Stormwater Guidelines and Best Management Practices for Protection of Fish and Fish Habitat, Department of Fisheries and Oceans, Draft, April 2001
113
Stormwater Planning: a Guidebook for British Columbia, Ministry of Environment, Province of British Columbia, May 2002
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Vancouver, The City of White Rock and Metro Vancouver with the monitoring of the Vancouver Public Library and White Rock Public Works building.114
4.3
OVERVIEW OF 2003/2004 GREEN ROOF MONITORING STUDY The Vancouver Public Library’s (VPL) Central Branch building and green roof were constructed in 1995. The 2,600 m2 roof includes an extensive green roof with a gross area of 1,850 m2 and a net area of 1,500 m2. The green roof was designed and completed by architect Moshe Safdie and Landscape Architect Cornelia Hahn Oberlander. The green roof is inaccessible to the general public but can be viewed by occupants in the surrounding residential and commercial towers. Another similar green roof project was undertaken at the Public Works Building of White Rock. The green roof at the City of White Rock was constructed in 2002. The building recently obtained a LEED® Gold certification and was recognized as the first building in Canada to obtain this status. Both green roofs were monitored from July 2003 through September 2004. Flow, rain, air and runoff temperature, humidity, solar radiation, wind speed and soil moisture were recorded every 5 minutes. A XP-SWMM computer model was calibrated using the results to evaluate the green roof function under various design storm conditions. IMPACT OF GREEN ROOFS ON REDUCING EFFECTIVE IMPERVIOUS AREA One of the major outcomes of the VPL and White Rock flow monitoring study was the development of an effective impervious area (EIA) relationship with growing medium depth. Since reducing EIA is a key objective in any watershed planning study, it is important to be able to calculate EIA reductions for green roofs. Figure 4-1 illustrates this relationship. Figure 4-1: EIA Versus Growing Medium Depth
114
For additional information, refer to the proceedings of the 2004 Green Roofs for Healthy Cities conference in Portland, Oregon and consult the paper “Vancouver Public Library Green Roof Monitoring Project”.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Figure 4-1 shows that 70% of the EIA reduction of a green roof occurs with the first 150 mm of depth. Additional depth produces decreasing benefit to EIA. Other research has shown that the relationship between growing medium depth and the stormwater benefits of a green roof is not as clear-cut as is indicated by these results from the calibrated XP-SWMM model. Monitoring results from BCIT and the Seattle GREP show that a greater percentage of runoff retention was achieved with a growing medium depth of 100 mm than with 150 mm in the Pacific Northwest’s rainy climate115. But the components of the growing medium (e.g. percentage of mineral soils and humus), the types of plantings and the design of the drainage layer all contribute to the water retention capacity of the green roof. Both studies had additional variables, such that the difference in runoff retention cannot be attributed only to growing medium depth. Therefore it must be recognized that depth of growing medium alone is not sufficient to characterize the expected stormwater benefits of the green roof system. But, in general, research does support the XP-SWMM results shown in Figure 4-1, assuming all variables other than growing medium depth are held constant. It has been found that the linear increase of retention with growing medium depth holds up to 5 cm depth, and the incremental benefit decreases above that value116, which is illustrated by the results in Figure 4-1. Also, a separate green roof modelling tool called LIDSWMM was developed as part of the Seattle GREP.117 The tool was used to model an ideal green roof using parameters from the FLL guidelines in order to show that it should be possible to achieve the stormwater volume reduction and rate control goals using only a green roof. The ideal green roof design that resulted was a single-layer green roof system conforming to FLL standards, with 150mm depth of growing medium. It is proposed then that the optimal depth of a green roof in Vancouver, based on a stormwater benefit only, is 150 mm. IMPROVING THE STORMWATER PERFORMANCE OF GREEN ROOFS Peak flow attenuation remains a goal that green roof design addresses but has not yet achieved at a level that meets the needs of stormwater design in the Pacific Northwest. In typical extensive green roofs currently installed in North America, once the growing medium becomes saturated, rainfall flows relatively quickly through the soil and into the under-drain system. The under-drain system is designed to move water as quickly as possible out to the roof drains such that ponding will not occur on the roof membrane. The trouble with this approach is that the water travels too fast through the saturated soil, thus failing to meet the flow rate control criteria in Table 4-1.
115
CONNELLY, 2006 and GAGNES, 2007
116
TRCA, 2007; Appendix A
117
GAGNES, 2007
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
More information, methods and technology are emerging that can improve this performance aspect of a green roof without compromising the roofing membrane. One method is to change the design of the under-drain system, which is evolving as green roof manufacturers improve and update their designs. For example, the interface at the growing medium could be partially impermeable in a pattern that would force rainfall to move vertically then horizontally then vertically. This would substantially increase the travel time as the horizontal movement of water through soil is slower than the vertical movement. The Seattle GREP found that current designs for cellular mat under-drain systems were still inadequate to reduce flow rates for the Pacific Northwest climate.118 The study’s authors recommend that aggregate drainage layers can perform up to ten times better for flow attenuation than cellular mats and may be cheaper, while tray systems seem to perform somewhere in the middle. More testing and research needs to be done on how to fully achieve the desired level of stormwater flow control with a green roof. If this can be achieved, a greater stormwater benefit will be realized and the business case can be adjusted.
4.4
RECEIVING WATER QUALITY IMPROVEMENTS Research has shown that provided growing mediums are deeper than 100 mm, green roofs are effective at removing atmospheric pollutants from rainfall.119 They are also effective at reducing negative thermal aspects of impervious area runoff. However, most of the urban pollutants that degrade receiving waters are generated at the street level. On the other hand, green roofs significantly reduce the volume of water leaving a rooftop during the smaller rainfall events such that end-of-pipe treatment facilities, if employed, can be reduced in size. It is likely that in the future, some form of end-of-pipe treatment will be required in highly urbanized watersheds (i.e. impervious areas greater than 50%); particularly as combined sewers are separated and frequently occurring rainfall events are discharged directly into the aquatic environments. Since most urban pollutants are washed off during these small rain events, an offsetting benefit could be calculated for the construction of green roofs. CALCULATING A GREEN ROOF WATER QUALITY SAVING Water treatment facilities and other best management practices (BMPs) are sized to remove pollutants from the smaller rainfall events. Typically, designers optimize the size of water quality facilities by predicting removal efficiencies using a continuous rainfall data set ranging over at least one year. Since no locally published research is available documenting the linkage between green roofs as a percentage of the watershed area and water quality BMP size, this report assumes that the effective impervious area (EIA)
118
119
GAGNES, 2007 TRCA, 2007; Appendix A
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
relationship developed in the VPL and White Rock Green Roof flow monitoring study can be used. To calculate this benefit, the 15th Avenue Trunk in the City of North Vancouver was selected as a pilot project. In order to reduce the pollutant loading into Wagg Creek, the City recently installed a high rate settling facility on their 15th Avenue storm sewer at a cost of $250,000. This facility is predicted to significantly reduce the loading of 50 micron and larger particles in the downstream creek system. Numerous studies have shown that many of the chemical constituents in stormwater attach themselves to grit in the stormwater stream. By removing these particles it is hoped that the water quality in Wagg creek improves. Assuming that this basic level of treatment is acceptable to meet the objective, a cost per square metre of impervious area surface can be calculated. To accurately develop this cost however, the design criteria used will have to be increased to meet DFO’s water quality criteria from their stormwater discharge guidelines. The facility will need to be tripled in size for a total cost of $750,000.
Basin size: 80 ha. Estimated cost of high-rate settling facility: $750,000. Percent total impervious area: 60%.
Unit cost to treat impervious area: $15,625 /ha ($1.56/m2 ). Assuming 150 mm green roofs are constructed in the basin to reduce the stormwater treatment requirement and that the effective impervious area of the 150 mm green roofs is 29%, the net benefit can be calculated as $1.56*(1-0.29) = $1.11 /m2. It could be argued however, that using high rate settling facilities that settle only the 50 micron and larger particle sizes does not provide sufficient treatment to meet the water quality guidelines. In fact, if a wetland were to be constructed similar to the Lost Lagoon facility in Stanley Park, the costs would be 20 times the above number (i.e. $22.20/m2) plus property acquisition costs. Property costs could double or triple that number again. TIMELINE FOR IMPLEMENTATION Currently, there is no political will to force municipalities to meet the effluent standards set by the aquatic water quality guidelines at a stormwater outfall other than if a federal grant is offered or a DFO authorization is required. Instead, senior governments have reluctantly agreed to receiving water monitoring programs that link future actions to exceedance thresholds using chemical and biological indicators. Should these thresholds be exceeded, stormwater quality treatment could be required. The green roof water quality benefit could then be used to offset future stormwater treatment facilities.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
4.5
REDUCTION IN MAJOR STORM FLOWS AND DEVELOPMENT COST CHARGES Depending on the municipality, storm sewers are sized to convey the 5 or 10-year storm event. Major overland flow routes, creek systems, culverts and canals are usually sized to convey the 100-year storm. With extensive green roof systems, water takes slightly longer to move through to the storm sewer even during saturated soil conditions. This delay reduces peak flows during storm events and hence can reduce the size of downstream drainage infrastructure. However, the delay reduces with increasing storm severity. Table 4-2 determines the expected percent reduction in peak flow under the 2, 5, 10 and 100-year return period using AES storm distributions and Burnaby mountain rainfall amounts. The results were developed using the calibrated XP-SWMM model on the VPL green roof and can be viewed as typical for Lower Mainland conditions. Table 4-2: Impact of 150 mm Green Roofs on Major Storm Flows1 Return Conventional PredevelopGreen Roof Peak Flow ment Flow Flow Reduction Period Roof Flow (L/s) (L/s) (L/s) (%) 2 2.39 1.16 1.71 55 5 3.10 1.48 2.23 54 10 3.58 1.61 2.57 51 100 5.07 2.73 3.64 61 1
Based on the results of an American Hydrotech and Soprema Roof System.
Since most municipalities size their storm sewers for the 10-year storm peak flow, it can be concluded that the 50% reduction in peak flow can equate to a reduction in sizing to downstream drainage infrastructure of roughly 50% from a 150 mm green roof. Referring back to section 4.3, if the travel time of rainfall through the saturated growing medium can be reduced as has been shown by some manufacturers, the peak flow reduction will be increased and the offsetting financial benefit increased as well. PROPOSED REDUCTION IN DEVELOPMENT COST CHARGES (DCCS) DCCs are charged to a developer to cover the cost of the off-site measures as a direct result of developing land. DCCs include the costs for downstream conveyance improvements including storm sewers, culverts, detention ponds and environmental BMPs. A 50% reduction in downstream infrastructure sizing is a significant amount. However, when translated to a reduction in DCC amount, it must be recognized that roughly 70% of construction cost is the trenching cost. A pipe diameter reduction of 1 or 2 sizes may only amount to 15% of the total cost. Therefore, it is recommended that municipalities consider reducing Development Cost Charges (DCCs) 15% for developments that implement green roofs into their design. A formal DCC study for green roofs would need to be carried out, but for the purposes of this report, we have assumed a 15% reduction is possible.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
To calculate the stormwater benefit of this item, the City of Surrey’s DCC bylaw was referenced. The average DCC cost for multi-family residential development in the city centre area is $15.61/m2. Assuming four-storey buildings and using a rooftop basis, this DCC can total $62.44/m2 of roof area. Reducing it by 15% carries a green roof benefit of $9.37/m2 of roof area. RE-DEVELOPING AREAS In areas that are already developed with a properly sized storm sewer, DCCs may not apply depending on the bylaws of a municipality. In these areas, it may be difficult to realize a saving. However, many older drainage systems in the Lower Mainland were sized based on limited climatic information using simplistic calculation methods. It is likely that existing capacity restrictions exist and will be identified in upcoming Integrated Stormwater Management Planning studies (ISMPs). As a result, it is felt that the $9.37/m2 savings is applicable to green roofs in re-developing areas as well.
4.6
REDUCTION IN RISKS DUE TO CLIMATE CHANGE A recent study by the University of British Columbia (UBC) assessed the potential effect climate change120 will have on municipal drainage infrastructure. Since most municipal drainage infrastructure design is based on the capacity to pass a design discharge, it is possible that any climate change that produces an increase in precipitation, or more importantly an increase in the intensity of precipitation, will increase the magnitude of the design discharges. Drainage infrastructure designed based on pre-climate change conditions may be potentially under designed and would not have the capacity to properly convey the higher design discharges. Green roofs have the potential to minimize the effect increases in precipitation have on design discharges, therefore reducing possible conveyance upgrading expenditures. The UBC study determined that there were strong increasing trends in short-duration rainfall intensities in its North Vancouver case study. Typically, discharge from developed areas that are greater than 50% impervious area, such as high-density multifamily high rise, commercial and institutional buildings, is governed by shorter duration storms (i.e. less than the 2-hour). It is these types of development that will be most affected by increases in rainfall intensities. By reducing the impervious area to less than 50% of the total area, longer duration storms will govern the discharge; therefore the climate change effect on the conveyance system will be minimized. For example, the UBC study showed that the 84 ha 15th Street catchment requires upgrades to approximately 1,000 metres of storm sewer trunk due to the increase in short
120
Denault et. al, 2001
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
duration rainfall intensities. These upgrades would cost approximately $550,000. By constructing green roofs on 2.8 ha within the catchment, the overall impervious area would be reduced to below the 50% threshold. The cost benefit of the green roofs in reducing the cost of the infrastructure upgrades would be $7.75/m2.
4.7
REDUCING THE STORMWATER IMPACT TO AQUATIC HABITAT It has recently been established that as the effective impervious area of basin increases, watershed health decreases. In fact, once the effective impervious area of a watershed exceeds 35% EIA, it is unlikely to support salmon populations at all. Metro Vancouver estimates that the region’s population will grow to nearly 3 million people over the next 30 years. Much of this growth will mean increased densities and a higher percentage of impervious surfaces. Metro Vancouver has estimated that unless stormwater source controls are implemented to maintain current EIA levels on all new buildings and sub divisions, most creek systems west of Langley will no longer be able to support salmon populations by 2036. Assuming then, that EIA levels are to be maintained, the purpose of this section is to examine the role that green roofs can play in maintaining a watershed’s EIA percentage. Watersheds can be broken down into two categories:
Developing Watershed: a watershed that contains undeveloped land with pressures to develop it.
Re-developing Watershed: a watershed that is fully developed, but is experiencing re-development pressures due to densification.
To maintain existing EIA levels, either the impervious area must remain constant, or additional impervious areas must be designed in such a way to “capture” rainfall. By “capturing” rainfall, a stormwater source control must be able to evaporate, transpire, infiltrate, or harvest up to a pre-determined amount of rainfall. This amount can vary and is defined in the DFO Stormwater Guidelines as the 6-month storm and in the B.C. Stormwater Guidebook as 50% of the Mean Annual Rainfall (MAR) event. For the Lower Mainland, this 24-hour rainfall amount ranges between 27 mm in the Southern areas to 45 mm or greater in the North Areas next to the mountains. ESTABLISHING GREEN ROOF BENEFITS IN DEVELOPING WATERSHEDS In developing watersheds, most municipalities charge DCCs to offset downstream improvements and require the land to be developed in such a way that it meets set stormwater criteria. DCCs cover costs associated with conveying stormwater off-site and costs to protect the environment. However, the costs of environmental protection measures are typically born by the land developer directly as part of their initial infrastructure costs as no formal process is in place to recover these on-site
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
environmental costs. For the purposes of evaluating the environmental protection benefit of green roofs in both developing and re-developing watersheds, it is proposed that these costs be allocated as part of the municipal costs in both cases. An example of the magnitude of this onsite environmental cost is for a single-family residential developer. Currently, when faced with the construction of an outfall to a creek system requiring a DFO authorization, developers have been paying upwards of $6,000 per lot for additional lot and road stormwater mitigation measures (excluding DCC costs) to meet the capture target outlined above. Approximately $3,000 of this cost is allocated to mitigation measures on the lot through the construction of rock pits, amended soils and rain gardens. Since typical roof areas are 186 m2, this translates to a cost of $16.15/m2 of roof area. For new multifamily, commercial, or industrial land uses in developing watersheds, the cost to capture rainfall can be far more expensive particularly with multifamily residential developments as the impervious surfaces are very large and the area available to construct any mitigative measures limited. Currently, there are no published examples of on-site stormwater capture costs for the non-single family land uses. For this reason, and for the purposes of this report, it is assumed that the costs are equivalent to the singlefamily land uses. To calculate the stormwater benefit, again, the City of Surrey’s DCC bylaw was referenced. The average DCC cost for multifamily residential development in the City Centre area is $15.61/m2. Assuming four-storey buildings and calculating on a rooftop basis, this DCC can total $62.44/m2 of roof area. It is proposed that the DCC cost is further reduced by $16.15/m2, in addition to the other noted savings benefits, to offset the cost of adding a green roof, provided the on-lot capture target is met by the green roof. ESTABLISHING GREEN ROOF BENEFITS IN RE-DEVELOPING WATERSHEDS In re-developing watersheds, the site level stormwater criteria is not clearly laid out. In this case, the land is already developed and the receiving environment has already felt the stormwater impact. As a result, if the proposed impervious area remains the same, no additional negative consequences will occur. However, this is normally not the case. For example, as single-family residential land uses are replaced by multi-family land uses, impervious areas will increase, thus degrading the downstream receiving environment. However, the environment makes no distinction between new development and redevelopment; any increase in impervious area degrades watershed health. For this reason, it is felt that green roofs in re-developing watersheds should also receive the $16.15 /m2 benefit either through a reduction in DCC charges or other equivalent methods such as density bonuses (to be discussed further in section 5). Based on research results and modeling of green roof parameters, a baseline green roof for the Metro Vancouver region is recommended to be an extensive type green roof with 150 mm depth of growing medium. Based on modelling of the estimated performance
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
and reduction in effective impervious area of the roof associated with a green roof, this type of roof could achieve approximately 70% reduction in EIA, which would provide significant benefits in reduction of volumes and peak flows in downstream infrastructure, mitigation for climate change impacts, and improvements to stormwater discharge quality and mitigating impacts to aquatic habitat. These benefits have been estimated on a per area basis for the baseline green roof case and the results are summarized in the table below. Table 4-3: Summary of Estimated Baseline Green Roof Stormwater Savings Estimated Stormwater Benefit Savings Receiving Water Quality Improvements $1.11/m2 Reduction in Major Storm Flows (DCC) $9.37/m2 Reduction in Risks Due to Climate Change $7.75/m2 Reducing Stormwater Impact to Aquatic Habitat $16.15/m2 TOTAL
$34.38/m2
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Section 5
Developing a Business Case for Green Roofs
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
5.
DEVELOPING A BUSINESS CASE FOR GREEN ROOFS
5.1
INTRODUCTION The business case developed in this report targets commercial, industrial and high rise multi-family buildings. The business case is likely not applicable to single family homes, or walk-up condos/townhouses. There are many papers published on the business cases for adopting green roofs throughout the world. Significant papers have also been written about the benefits of Green Roofs/Eco-Roofs in the Lower Mainland.121 The results however, tend to depend heavily on the local climate, building style and materials, public acceptance and environmental protection legislation. For example, in Central North America, there is a strong case for using green roofs to reduce energy costs due to summer air conditioning. Unfortunately, this is not the case in Metro Vancouver as the air conditioning demands are far less, significantly reducing the offsetting benefits. The main benefits of green roofs have typically fallen into the following categories: 1. 2. 3. 4. 5. 6. 7. 8. 9.
Aesthetics and Property Values; Agriculture; Energy – Cooling & Heating; Green House Gases and CO2 Sequestration; Heat Island Effects; Air Quality; Stormwater; Roof Life; and Terrestrial Habitat.
These benefits are described in Table 5-1, which also indicates whether the recipient of the benefit is the developer, owner or community. Monetary values will be assigned to the above benefits and the benefits will then be compared to green roof construction costs. Significant effort will be placed on the stormwater benefits as we feel it to be the superior benefit in Metro Vancouver. Also, financial mechanisms such as density bonuses, sewer utilities and development cost charges, are already in place and can be easily modified to promote green roof construction provided the above caveats are met. As in the previous section, the business case analysis here looks at the use of an extensive green roof for installation in the Metro Vancouver region. For this section, the analysis 121
Eco-Roofs and Vancouver: A Critical Analysis. URL: http://www.sustainable-communities.agsci.ubc.ca/thesis/kp-7.pdf
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
was not limited to an assumed 150 mm depth of growing medium. Also, several growing medium depths are reviewed to show the implications that the growing medium depth can have on the costs of implementation.
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Table 5-1: Summary of Green Roof Benefits and Benefit Recipients Benefit
Description
Aesthetics and Property Values
In urban areas where tall and short buildings are interspersed, there are significant benefits to the neighbouring properties. Also, where green roofs can be incorporated into the design of open areas, they can significantly improve the saleability of a particular development, and the local area as a whole. There is a growing movement to expand the successful community garden concept and link it to green roofs. This allows residences in higher density areas to also enjoy the benefits of being able to establish community gardens. Green roofs do add to the “R” factor of a building, however, it is argued that during the winter, these positive effects are small due to the positive conductivity of the growing medium. The biggest energy benefits tend to be in the summer, as green roofs tend to be very effective at moderating the membrane temperature. Another benefit often cited is the reduction of CO2 levels due to plant growth on green roofs. Unfortunately, the majority of green roofs in North America tend to have very small plantings due to the dominant use of extensive roof systems using shallow growing mediums. This category would offer more benefit if all roofs were intensive with larger plant life, but would likely be off-set by the higher structural costs. Green roofs offer a very credible solution to lowering the street temperature of cities in the summertime. A recent study in the City of New York found that construction of green roofs in Manhattan could possibly cut the urban heat island effect nearly 40%. This was then related to a reduction in health costs. Similar to the proven impacts of planting of urban forests, green roofs can also have a positive impact on air quality by filtering the air and intercepting air pollutants. The impact will again be determined by the size of the plantings and is often only measurable with intensive roof systems. Green roofs capture, detain, filter, and cool rainwater. This can provide significant benefits to the downstream in-stream aquatic habitat, and receiving water quality. Off-site stormwater infrastructure and facilities can be reduced in size or even eliminated in some cases through the construction of green roofs. Green Roofs can also provide significant benefits to the downstream municipal stormwater system in urban centres where impervious percentages are greater than 50%. A recent climate change study by Metro Vancouver has shown that there is a real concern that should trends of the past 25-years continue, convective storms are increasing in intensity. Areas with impervious ratios over 50% will see their flows increase. It has been observed that a green roof significantly extends the life of the underlying membrane by moderating its temperature and removing ultraviolet radiation. This benefit may offer significant cost savings by way of preventing or delaying roof repairs and prolonging roof life. It has been documented that there is a positive benefit to urban bird species due to the construction of green roofs. Nesting occurs on many of Vancouver’s existing roofs. There may be an opportunity to allocate terrestrial habitat credits to green roofs.
Agriculture
Energy – Cooling and Heating Green House Gases and CO2 Sequestration Heat Island Effects Air quality
Stormwater and Environment Stormwater, Municipal Infrastructure, and Climate Change Roof Life
Terrestrial Habitat:
; Benefit is realized in other jurisdictions and could be in the Lower Mainland if a financial recovery structure was set up. ; Benefit can be realized today.
Benefit Recipient Developer Owner Community
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
5.2
COST-BENEFIT RATIOS There is a disconnect between who bears the cost of a green roof and who benefits. A developer may erect a building intending to sell it as soon as constructed. To keep costs low and maximize profits, amenities like green roofs will not be included unless required or encouraged. However, the benefits of a green roof can accrue directly to owners or to the broader community. “The mitigation of urban stormwater runoff represents by far the most influential potential impact of eco-roofs in Metro Vancouver”, according to Steve McTaggart, an assistant sewers engineer for the City of Vancouver, and in “… parts of the region where combined sewer systems service a large, continuous area, even moderate reductions in stormwater runoff could help offset combined sewer overflows”.122 There is recognition of the need to see return on investment within a certain time period, but the extent of that time period can vary significantly. The Penn State Centre for Green Roof Research is looking for an investment return period of 5-7 years.123 By comparison, German cost-benefit analyses for green roofs usually cover a 40-year investment period.
5.3
COST OF A CONVENTIONAL ROOF The cost of a conventional 2-ply SBS roofing system on top of concrete is currently $86 $129 per square metre in the Lower Mainland.124 This increased significantly, by about $32/square metre, between approximately 2001 to 2004 to cover increased insurance costs, in large part due to fires.125
5.4
COST OF A GREEN ROOF BASIC COSTS (EXCLUDING STRUCTURAL COSTS) The estimated basic cost of a green roof varies from $184/m2 for a 100 mm growing medium depth to $238/m2 for a 300 mm growing medium depth. The baseline green roof standard used for the business case analysis is 150 mm growing medium depth, which has an estimated basic cost of $205/m2. A summary of basic green roof costs is presented in Table 5-2.
122
Anon.: pp. 83 and 88
123
Beattie, p. 108
124
Tom Locke, Aquaproof, Pers. Comm., Dec. 2004 and City of Toronto, 2005
125
Jim Watson, RCABC, Pers. Comm., Dec 2004
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Table 5-2: Summary of Basic Green Roof Costs (Metric) Growing Medium Green Roof Envelope Costs ($/m2) Total Nominal Mass Drains/ Fabrics/ Growing Plants Depth (kg/m2) Membrane Medium Cost 100 mm 152 $21 $162 $11 $184 150 mm 226 $21 $162 $22 $205 200 mm 299 $21 $162 $33 $216 300 mm 445 $21 $162 $55 $238 600 mm 890 $21 $162 $77 $260
Referring to section 3.10, the reported green roof installation costs in Germany are about $40/m2. The reported installation costs in North America range from $80 to $200/m2.126 The costs in the above table are at the upper end of the range as they represent 2005 construction levels and thicker growing mediums to achieve a stormwater benefit based on west coast rainfall. While the costs are still considerably higher than in Germany due to lack of economies of scale and relative lack of experienced companies in North America that have specialized in this area, there is some evidence that North American costs are starting to come down. TRCA (2007) found the average reported green roof installed cost to be $112/m2 which was based on green roofs with varying thickness of growing medium. STRUCTURAL COSTS A green roof has weight implications on the structure below it. The significance of this structural load in terms of structural design and costs depends on the weight of the proposed green roof, and the location of heavier areas (e.g., deeper soil depths for larger plants) in relation to columns and other structural bearing members. All green roof projects require the services of an experienced structural engineer. For a new building, the cost of the additional roof structure to support the weight of the green roof will increase approximately proportional to the percentage increase in weight of the structure. It takes a heavier structure to carry the extra load and the cost of the material for the structure will go up by approximately the same amount. The addition of a green roof will have a larger impact on the cost of lighter structural materials (wood and structural steel) than it will on heavier structures (such as concrete). A summary of the additional structural costs associated with a green roof is provided in Table 5-3. The costs are based on the following roof structure construction costs: 126
wood – $86 to $108/m2; steel – $161 to $194/m2; and concrete – $269 to $301/m2.
Beattie, 2004 and TRCA, 2007
5-5
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
In the current building market it is very difficult to define a single value construction cost. Also, the total cost of the structure will fluctuate depending on how many floors and spans there are. For the cost analysis, the middle of these cost ranges was used: $91/m2, $178/m2 and $285/m2 for wood, steel and concrete respectively. These costs are limited to the structure of the roof. Vertical structural elements will also be affected but to a much lesser extent. Foundations will also be affected but this will depend on the percentage of increase in load on the foundation. For example there will be little impact in a 24-storey tower and greater impact in a one-storey building. Table 5-3: Summary of Additional Structural Costs Incremental Increase in Growing Medium Cost of Roof Structure (Moist Condition) with Green Roof (%) Mass Nominal Depth Wood Steel Concrete (kg/m2) 114 161 97 19 75 mm
Incremental Increase in Cost of Roof Structure with Green Roof ($/m2) Wood
Steel
Concrete
$156/m2
$172/m2
$54/m2
100 mm
152
208
125
25
$205/m2
$226/m2
$75/m2
150 mm
226
308
185
37
$301/m2
$328/m2
$108/m2
200 mm
299
408
245
49
$398/m2
$436/m2
$140/m2
300 mm
445
608
365
73
$592/m2
$646/m2
$205/m2
These structural costs, developed using 2005 cost data, may be on the high side. Most new building designs accommodate the cost of a structural upgrade for the green roof from the initiation of the project, such that the incremental cost is not broken out. In a 2007 survey127, only one response out of 24 in Southern Ontario could report the cost of the structural upgrade due to the fact that the green roof was added after the preliminary design had been completed and priced out. The incremental increase in actual cost was $54/m2 for a 2-storey building, which is the lowest cost shown in Table 5-4. TOTAL COSTS For the baseline standard green roof with growing medium depth of 150 mm, the total estimated cost of a green roof, including envelope and structural upgrade costs, ranges from $312/m2 in a concrete structure to $533/m2 in a steel frame structure. (See Table 5-4).
127
TRCA, 2007
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER Table 5-4: Total Cost of a Green Roof Depth of Growing Medium Depth 100 mm 150 mm 200 mm 300 mm
Wood $398/m2 $506/m2 $614/m2 $829/m2
Total Cost of Green Roof ($/m2) Steel $420/m2 $533/m2 $651/m2 $883/m2
Concrete $269/m2 $312/m2 $355/m2 $441/m2
The estimated total cost of green roof construction including the structural component is rarely reported, likely due to the difficulties in separating these costs from the building costs. However, the structural costs are significant in wood and steel buildings and cannot be ignored. Concrete buildings can accommodate the increased loadings relatively easily, but the estimated total cost of the green roof still adds a 53% premium on the basic roof cost, assuming a 150 mm roof. Manufacturers continue to work on providing all the benefits of a green roof for less saturated weight and the costs herein should perhaps be viewed as a yardstick for structural and total cost considerations. Each project should be individually reviewed by a structural engineer to evaluate the impacts of incorporating a green roof.
5.5
SAVINGS FROM A GREEN ROOF The savings associated with the benefits of an extensive green roof implemented in the Metro Vancouver region are tabulated in Table 5-5. The research which supports these calculations is provided in Appendix B. The total benefit of a green roof with a minimum growing medium depth of 150 mm, in Metro Vancouver, was calculated to be $83.47/m2. Of this amount, $43.60/m2 is due to the longer life of the waterproof membrane, and $34.37/m2 accrues from potential stormwater management benefits. The incremental difference between a green and conventional roof per square metre for wood, steel and concrete respectively is estimated at $314, $341 and $120 as shown in Table 5-6.
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Table 5-5: Details of Green Roof Benefits Results from Literature Search Value of Published Benefit Benefit $/m2/year Aesthetics and Property Values Agriculture Energy - Cooling Energy - Heating
Unquantified at this time. Fairmont Hotel Vancouver – green roof herb garden. NRC – Ottawa green roof pilot study showed 75% reduction in cooling costs.
$0.00 $141.00 N/A
NPV (1)
Conversion to Vancouver Conditions Value of Conversion Benefit Method $/m2/year
$0.00
N/A Direct application if opportunity exists $2120.00 (unique case). Transferred to Vancouver conditions by factoring 265 Degree cooling N/A hours to 65 degree cooling hours.
Benefit Recipient NPV (1)
$0.00
$0.00
$0.00
$0.00
$0.37
$5.49
N/A
N/A
N/A
N/A
N/A
N/A
Unquantified at this time.
N/A
N/A
N/A
N/A
N/A
Green House Gases and CO2 Sequestration Heat Island Effects
New York City Health cost reduction.
Air Quality
N/A
Stormwater and Green roofs improve water Water Quality quality. Stormwater and Major Storm Green roofs reduce runoff effects. Flow DCCs Stormwater and Green roofs reduce runoff effects. Climate Change Stormwater and Green roofs reduce urbanization Aquatic Habitat effects. A conventional roof lasts 20 Roof Life years. A green roof lasts 40 years. Terrestrial Green roofs provide habitat. Habitat
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Value of benefit calculated by KWL for this report.
N/A
$1.11
N/A
N/A
Value of benefit calculated by KWL for this report.
N/A
$9.37
N/A
N/A
N/A
$7.75
N/A
N/A
N/A
$16.15
N/A
$43.60
Direct application.
N/A
$43.60
N/A
N/A
N/A
N/A
N/A
Value of benefit calculated by KWL for this report. Value of benefit calculated by KWL for this report.
$83.47
Note: (1) NPV – Net Present Value over 40 years at a discount rate of 6%
Benefit is realized in other jurisdictions and could be in the Lower Mainland if a financial recovery structure was set up. Benefit can be realized today.
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TOTAL GREEN ROOF BENEFIT IN METRO VANCOUVER
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Table 5-6: 150 mm Green Roof Cost-Benefit Analysis Summary Value ($/m2) Wood Steel Concrete Cost of Green Roof $506 $533 $312 Green Benefit -$84 -$84 -$84 Conventional Roof
-$108
-$108
-$108
Total Incremental Cost
$314
$341
$120
In other words, if the green benefit could be doubled, the incremental costs would be neutral in the concrete building scenario. The subsidies could likely be reduced over time as costs begin to move closer to European costs.
5.6
CASE STUDY 1 – “THE SILVA” BUILDING IN NORTH VANCOUVER OVERVIEW OF DEVELOPMENT, CONSTRUCTION AND INSTALLATION The Silva high rise development is located in Central Lonsdale area of the City of North Vancouver. The building was constructed by “West Coast Projects Ltd. of Vancouver”. The 67-unit building was fully supported by the City as it represents the City's commitment to pursue opportunities that will support its goals for a sustainable community. Completed in February 2005, the 67-unit concrete development achieved LEED® certification from the U.S. Green Building Council (USGBC). LEED®, also known as Leadership in Energy and Environmental Design, is a green building rating system that sets the national standard for developing high performance, sustainable building. The Silva was the first Canadian residential/commercial building recognized by LEED®. The Silva includes 8,175 square metres of residential space and 446 square metres of commercial space. Developed by 16th Street Development, the building was completed on time and under budget. The Silva was quickly sold out upon completion indicating a positive trend in the housing market. The purpose behind the LEED® system is to: • • • • • •
define “green building” by establishing a common standard of measurement; promote integrated, whole-building design practices; recognize environmental leadership in the building industry; stimulate green competition; raise consumer awareness of green building benefits; and transform the building market.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
The Silva building was the first LEED® Certified building constructed by West Coast Projects. Discussions with the owner of West Coast Projects revealed that the LEED® Certification was a positive experience and the construction practices and materials required for LEED® certification made sense. TECHNICAL AND DETAILED DESIGN INFORMATION Table 5-7 shows the project facts and statistics of the Silva Project. Figure 5-1 shows a photograph of the eastern section of the green roof. Table 5-7: Green Roof Facts for the Silva Building
Developer Contact: Green Roof Area Location of Green Roof Roof Construction Material Access for Public ? Roof Membrane Type Growing Medium Depth: Completion Date:
West Coast Projects Limited 1040 Georgia Street East, Vancouver, BC V6E4H1 (604) 685-2303 David Sprague 418 square metres 2nd floor over top of the commercial area Concrete Yes, incorporated into an amenity area American Hydrotech 600 mm February 2005
Figure 5-1: Eastern Section of the Silva Building Green Roof
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
OPERATION AND MAINTENANCE REQUIREMENTS Since the growing medium of The Silva’s green roof is substantial, it was decided that an irrigation system would not be required. It is anticipated, however, that some manual irrigation may be required for the first three years to establish healthy root systems. COST OF THE GREEN ROOF (EXCLUDING STRUCTURAL COSTS) Table 5-8: Green Roof Construction Costs for the Silva Building Constructed Construction Green Roof Construction Item Area Cost ($)128 Cost for drainage: Cost for soil (special soil mix) Cost of landscaping (special grass and plants) Cost of irrigation typical spec.(not required) Waterproofing (Hydrotech): Total Cost per Square Metres (using green roof area)
418 m2 418 m2 418 m2 418 m2
$9,100 $ 24,000 $28,000 $0 $13,500 $74,600 $178/sq.m.
The reported costs are likely low as they represent the raw sub-contractor’s costs. Missing is likely the line items of covering the prime contractor markup, insurance and mobilization/demobilization. For this reason, it is possible that the costs are 30% low. Marking the $178/m2 up by 30% yields a green roof cost of $231/m2. However, the estimated green roof construction cost for a 600 mm thick roof in Table 5-2 is $260/m2. The resulting difference in cost between The Silva green roof and the estimate appears to be mostly in the cost of the membrane. Based on the above, it appears that the Silva building costs are similar to those in Table 5-2. The costs might also be closer to 260/m2 if the green roof were installed at a higher level rather than on a two-storey building. LESSONS LEARNED The Silva highlights the use of a green roof system that was easily constructed on the 2nd level of a 16-storey residential tower. Once the developer committed to building a green building and striving to obtain a LEED® certification, the green roof above the commercial retail space became an easy decision. Changing construction practices to recycle materials and use more sustainable products “just made sense” to the developer. It also appealed to City staff and council, who assisted the developer by reviewing and processing the development’s paperwork smoothly and in a timely manner.
128
Raw sub-contractors cost from Brent Rassmusen, Marcon Construction, Pers Communications, May 2005
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
The premium for constructing the 600 mm deep green roof was small as the alternative was to construct an open area for residents to gather. The incremental cost for the green roof over the alternative was 8% or $6,000129. This small incremental difference was easily justified given the stormwater benefits of the green roof and the LEED® credits awarded. It also represents a significant lesson learned as it appears that there is a solid business case to construct green roofs in mixed commercial/residential high rise developments. GREEN ROOFS AND MULTI-STOREY TOWERS The second roof over the 16th storey of the multi-family residential tower was not constructed as a green roof. Although the costs would have been higher as the same business case may have not been available, the main reason West Coast Projects did not pursue this option was due to the perceived difficulty in eventually replacing the roof membrane130. At sixteen storeys in the air, removal and replacement of the green roof in order to repair or replace the roofing membrane would be a significant challenge. The above concerns by West Coast Projects are not isolated. The concerns were also expressed by the developers interviewed in section 3.16. The concerns can be addressed, but will take time for research and experimentation to prove out approaches. The concern about leak repairs can be dealt with through Electric Field Vector Mapping (EFVM) – a process performed by International Leak Detection and others, as mentioned in section 3.4. More research is required on the replacement of the membrane below a green roof after its design life has ended. It is certainly possible that the growing medium can be moved from one part of the roof to another, but the structural loads would have to be reviewed. Since roof tops are designed to take a considerable snow load, there is ample opportunity to move the soil around, but it still raises a valid concern.
5.7
CASE STUDY 2 – THE WHITE ROCK OPERATIONS CENTRE The City of White Rock decided to replace their operations centre with a new facility with the mandate to make it as “green” as reasonably possible. This approach was undertaken in accordance with the City's own policy of promoting green strategies in all their developments and planning strategies. The new operations centre opened in the spring of 2003, and received a LEED® Gold rating, making it the first new building in Canada to achieve this standing. The new facility is designed over land that housed an abandoned sanitary treatment plant, using the existing buried tank walls as the foundations for the new building. The building
129
Brent Rassmusen, Marcon Construction, Pers Communications, May 2005
130
David Sprague, West Coast Projects, Pers Communications, April 2005
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
developed into two separate pavilions: a two-storey component on the north end and a one-storey building on the south end. The north building is built on the existing basement of the old sewage treatment plant control building and houses the departmental elements which are only periodically used (field crew facilities, change rooms, first aid room, meeting and lunch rooms). The south building houses the office component of the department, the roof of which will be partially used as a roof deck and the majority of it made into a planted roof. TECHNICAL AND DETAILED DESIGN INFORMATION Table 5-9: Green Roof Facts for the White Rock Operations Building City of White Rock Developer 877 Keil Street, White Rock, BC, V4B 4V6 (604) 541-2181 David Pollock, P.Eng. Contact: 200 square metres Green Roof Area 2nd Floor over top of the office spaces Location of Green Roof Wood Roof Construction Material No Access for Public ? Soprema Roof Membrane Type 100 mm Growing Medium Depth: March 2003 Completion Date:
Figure 5-2: The Green Roof at the White Rock Operations Centre
Photo credit: BCIT at http://www.greenroof.bcit.ca
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
COST OF THE GREEN ROOF Again, similar to The Silva, it has been difficult to accurately separate the green roof costs from the other building costs. The reported cost of the 100 mm thick roof is $150/m2. The additional cost of the green roof over that of a conventional roof is reported to be approximately $17,225 or $86/m2 resulting in a base cost for a conventional roof at $64/m2. It is interesting to note that the difference between the estimates reported in section 5.3 for green roof and conventional roof construction costs are $44/m2 (i.e. $194/m2 less $150/m2) and $33/m2 (i.e. $97/m2 less $64/m2) respectively. Since the roof was constructed in 2002, it is likely that the membrane costs have increased by the $32/m2 difference noted by the RCABC. For these reasons, it is recommended that the costs in section 5.3 remain valid for the cost-benefit exercise. LESSONS LEARNED The City of White Rock has had trouble keeping the vegetation sustained over the summer. This could be due to lack of a formal irrigation schedule, the shallow growing medium thickness of 100 mm, or choice of plant material or a combination of issues. With the exception of the vegetation, the roof is reportedly functioning well and has begun to provide habitat for the local bird population.
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Section 6
Strategy for Implementation and Conclusions
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
6.
STRATEGY FOR IMPLEMENTATION AND CONCLUSIONS
6.1
INTRODUCTION The purpose of this chapter is to review the business case developed in section 5, and determine where the next steps should be. This section also provides some possible incentives to increase the “benefit” side of the equation.
6.2
REVIEW OF BUSINESS CASE FOR GREEN ROOFS Table 6-1 provides a summary of the previous sections. Generally speaking, there are currently insufficient benefits to offset the costs of constructing green roofs. The exception to this conclusion is the mixed commercial and high rise residential sites such as the Silva building whereby the cost of the green roof was offset by public open spaces on the 2nd level. Table 6-1: 150 mm Green Roof Cost-Benefit Analysis Summary Value ($/m2) Wood Steel Concrete Cost of Green Roof $506 $533 $312 Green Benefit -$84 -$84 -$84 Conventional Roof
-$108
-$108
-$108
Total Incremental Cost
$314
$341
$120
However, in assembling this report, the following deficiencies have appeared:
Development Cost Charges (DCC) are likely too low to collect sufficient funds to protect fisheries resources. More specifically, DCCs have been developed to protect against downstream flooding and erosion and not to protect against the environment. ACTION: consider either implementing a stormwater bylaw that deals with this deficiency, or develop DCCs that more accurately reflect the cost of providing water treatment and volumetric reduction targets.
Green Roof Construction Costs: Germany is able to construct green roofs for 25 to 50% of the current costs in North America. Economies of scale will obviously benefit the business case. In fact, if the green roof costs were reduced by 40%, there would be a strong business case for green roofs on concrete structures. ACTION: consider implementing a short term incentive program to build the economies of scale into the system (see section 6.3)
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
6.3
INCENTIVES It is not just greater environmental culture and lower costs that have led to the boom in green roof installation in Germany. Federal, state and local governments in Germany have developed a suite of incentives – both regulatory and financial – to encourage or mandate green roof construction. A summary of these from Ngan (2004) are presented below:
Direct Financial Incentives: Many jurisdictions offer subsidies for the implementation of green roofs. For example the city of Portland, Oregon has an incentive of $48/m2 for eco- (green) roofs as part of their initiative for ecological and sustainable water management. The funding is derived from pollution fees. The roofs must have 10 centimetres or more of growing medium and meet other design criteria to qualify for the incentive.
Indirect Financial Incentives: Stormwater disposal fees are charged by a growing number of German municipalities and are seen by green roof proponents as a very important incentive. Stormwater fees are calculated according to impervious surface area. The annual fee ranges from 0.20€/m² to more than 2.00 €/m² ($0.32-$3.20/m²). Green roofs may also qualify for a stormwater fee discount; again, there is a wide range but a typical discount is 50%. For green roofs not connected to the sewer system, the fee is not charged at all. In North America, stormwater disposal is generally not charged. Until our cities view stormwater runoff created by impervious areas as a real cost, little progress will be made.
Ecological Compensation Measure: Under the Federal Nature Conservation Act in Germany, green roofs may be built as a compensation measure for developments that cause impairment to the natural functions (e.g. infiltrating stormwater, providing animal and plant habitat, etc.) of a particular site.
Development Regulations: Especially in new developments where new buildings go through a development approval process, integrating green roofs into the development regulations is common and effective.
In North America, there are fewer examples of green roof incentives but they are growing – for example:
6-2
The Office of Energy Efficiency of Natural Resources Canada recently announced that green roof technologies may now qualify under its existing funding programs for energy efficient buildings – the Energy Innovators Initiative (EII), Commercial Building Incentive Program (CBIP) and the Industrial Building Incentive Program (IBIP).
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
6.4
The City of Portland has introduced density bonuses and stormwater management credits for green roofs (see below). Portland’s initiatives may be worth examining more closely for examples that are applicable to the Lower Mainland.
The New York State Assembly has passed a bill to provide a USD $48.44/m2 tax credit to defray the costs of installing a green roof in New York City.
EXISTING GREEN BUILDING INCENTIVES Another method of providing an incentive is to facilitate the wide-spread acceptance of green buildings such as the LEED® rating system. By providing special privileges for developers who implement green buildings and LEED® certifications, green roofs will undoubtedly follow. The favourable treatment that the developers of the Silva building (and others) received will likely result in those firms continuing the green trend.
6.5
DENSITY BONUS Portland has been a leader in promoting the use of eco-roofs with growing medium depths between 50 mm and 150 mm, and has been actively involved in several pilot projects. An eco-roof density bonus option is provided in the Central City:
Where the total area of eco-roof is at least 10% but less than 30% of the building’s footprint, each square metre of eco-roof earns one square metre of additional floor area.
Where the total area of eco-roof is at least 30% but less than 60% of the building’s footprint, each square metre of eco-roof earns two square metres of additional floor area.
Where the total area of eco-roof is at least 60% of the building’s footprint, each square metre of eco-roof earns three square metres of additional floor area.
The City of Portland defines roof gardens as landscape areas over slab with growing medium depths of 200 mm or more. Both eco-roof and roof gardens are treated as pervious area in the City’s stormwater management calculations.
6-3
Section 7
Summary
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
7. SUMMARY The variety of social, environmental, and downstream infrastructure benefits that would accrue from widespread implementation of green roofs in the Metro Vancouver region create a tantalizing vision of a cleaner, greener and more sustainable dense urban area. While green roofs, in one form or another, have been installed in this area for over 35 years, they are not yet prevalent, and it may be up to the regional districts and municipalities to create an encouraging climate for increased green roof implementation. Particularly given the increasing public and governmental concerns regarding urban impacts, environmental degradation, and global climate change, the situation appears to be favourable for increasing green roof coverage. Research has shown that the benefits of green roof construction include:
Stormwater Management Energy Efficiency Urban Heat Island Mitigation Increased Roof Membrane Lifespan Air Quality Improvements Improved Urban Aesthetics Improved Property Values Urban Agriculture Increased Biodiversity and Habitat Preservation Noise Mitigation
And yet even with all the research that has been done on green roofs, there remain challenges for implementation in the Metro Vancouver region, including:
Misconception associating green roofs with “leaky condo syndrome” Difficulty of repairs and maintenance Structural concerns Availability of expertise Limited local scientific research Fear of the “unknown”/ lack of local market data Cost Lack of standards Insurance coverage Fire hazard and uplift Aesthetics of flat roofs and “messy” look
For many of the above challenges, the best solution is or involves education, including education of municipal staff and building officials, designers, contractors and installers, and the general public. Though a long-term effort, education will help ameliorate many, though not all, of these concerns. In addition, various organizations are currently working on these issues such as regional and national building standards for green roofs,
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
insurance guidelines to assist insurers in evaluating green roofs and more scientific research projects to further define the design parameters and benefits of green roofs in this region. According to developers, the single most critical factor in deciding whether or not to put a green roof on a structure is cost.131 A green roof will always cost more than a standard roof installation. In this report, it has been demonstrated that a significant portion of the cost difference can be allocated to stormwater benefits that are realized downstream of a green roof installation. This exercise shows that the estimated cost savings benefits of green roofs do not currently out-weight their estimated costs, but as the case study on the Silva building indicates, net costs can be minimal. Furthermore, by more accurately tracking the true costs of the damage to the environment and by either increasing DCCs or strengthening stormwater bylaws and allowing the economies of scale to lower construction costs, the business case for green roofs on concrete structures will likely be met. The design of green roofs is evolving as more research in the Pacific Northwest helps us determine how best to achieve the stormwater management benefits required – especially during the high volume/saturated winter months. Specifically, more research is required on varying the composition and depth of substrate material and plant species to mitigate the seasonal variations in discharge. Current designs, from a stormwater management perspective, focus on volume reduction rather than peak flow reduction or water quality. A design needs to be capable of addressing all these components to effectively control runoff since stormwater DCCs are currently based on the size of downstream piping systems. In addition, for an individual project, energy and other benefits such as visual appeal should also be accounted for in considering the costs of a green roof. It is clear that green roofs represent a more expensive solution to stormwater management than comparable surface-installed systems. Because of this, their application is better suited to higher density areas where there is little room for ground surface stormwater mitigation measures. Further, since the costs to support the weight of green roofs can be considerable, concrete structures represent the most cost-efficient building type for green roof installation. Based on the above considerations, the most promising opportunity for green roofs appears to be multi-storey concrete buildings in higher density areas. This situation minimizes the cost, and maximizes the benefits, of the green roof due to urban density. Through the evolution of support and incentive programs in the Metro Vancouver region, the number and visibility of installations will expand. As this happens, developers, installers, insurers, and the public will become more informed about and comfortable with green roofs, and eventually, costs are expected to decrease as the local base of green roof knowledge and experience grows.
131
Davis, 2002
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Section 8
References
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
8. REFERENCES Adam, S. and Marriott, D. (2006) “2006 Stormwater Management Facility Monitoring Report Summary”, Bureau of Environmental Services, City of Portland. Akbari, H., Pomerantz, M. And Taha, H. (2001) “Cool Surfaces and Shade Tress to Reduce Energy Use and Improve Air Quality in Urban Areas”, Solar Energy, 70:3, 295-310. Banting, D., Doshi, H., Li, J., Missios, P., Au, A., Currie, B.A. and Verrati, M. (2005) “Report on the Environmental Benefits and Costs of Green Roof Technology for the City of Toronto”. URL: http://www.toronto.ca/greenroofs/pdf/fullreport103105.pdf Bass, B. (2001) “Addressing urban environmental problems with green roofs”, Encyclopaedia of Global Environmental Change, vol. 3, John Wiley & sons, Chichester, U.K... Brenneisen, S. (2003) “The Benefits of Biodiversity from Green Roofs – Key Design Consequences”, Greening Rooftops for Sustainable Communities, Chicago, IL Christian, J.E. and Petrie, T.W. (1996) “Sustainable Roofs with Real Energy Savings”, Proceedings of the Sustainable Low-Slope Roofing Workshop, ed. Desjarlais, A., Oak Ridge National Laboratory, Oak Ridge, Tennessee, p99. CMHC (2002) “Fairmont Waterfront Hotel Green Roof Herb Garden Case Study, Vancouver, British Columbia”, Innovative Buildings, Canadian Mortgage and Housing Corporation. Connelly, M. and Hodgeson, M. (2008) “Sound Transmission Loss of Green Roofs”, Sixth Annual Greening Rooftops for Sustainable Communities Conference, Awards and Trade Show: Proceedings. April 30 to May 2, 2008, Baltimore, MD. Connelly, M. and Liu, K.K.Y. (2005) "Green roof research in British Columbia - an overview," Greening Rooftops for Sustainable Communities, Washington, DC (NRCC-48203) URL: http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48203/ Connelly, M., Liu, K.K.Y. and Schaub, J. (2006) "BCIT Green roof Research Program Phase 1” URL: http://commons.bcit.ca/greenroof/publications/CMHC%20ERP%20Final%20060910.pdf Currie, B. and Bass, B. (2005) “Estimates of Air Pollution Mitigation with Green Plants and Green Roofs Using the UFORE Model”, Greening Rooftops for Sustainable Communities, 3rd annual conference, Washington, DC. Czemiel Berndtsson, C., Emilsson, J., and Bengtsson, L., “The Influence of Extensive Vegetated Roofs on Runoff Quality” EBN (2001) “Environmental Building News”, November 2001, p11.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Eumorfopoulou, E. and Aravantinos, D. (1998) “The Contribution of a Planted Roof to the Thermal Protection of Buildings in Greece”, Energy and Buildings, 27:29-36. David Evans and Associates, Inc and ECONorthwest (2008) “Cost Benefit Evaluation of Ecoroofs”, City of Portland Bureau of Environmental Services, Watershed Services. URL: http://www.portlandonline.com/BES/index.cfm?c=48725&a=222494 FLL (2002) “Guidelines for the Planning, Execution and Upkeep of Green-roof Sites” English Edition, FLL. Gangnes, D. (2005) “Seattle Green Roof Evaluation Project – Winter 2005”, Magnusson Klemencic Associates. Gangnes, D. (2006) “Seattle Green Roof Evaluation Project – Spring 2006”, Magnusson Klemencic Associates. Gangnes, D. (2007) “Seattle Green Roof Evaluation Project – Final Report March 2007”, Magnusson Klemencic Associates. Gedge, D. (2003) “From Rubble to Redstarts...Black Redstart Action Plan Working Group”, Greening Rooftops for Sustainable Communities, Chicago, IL. Graham, P. And Kim, M. (2003) “Evaluating the Stormwater Management Benefits of Green Roofs Through Water Balance Modeling”, Greening Rooftops for Sustainable Communities, Chicago, IL Gutteridge, B. (2003) “Toronto’s Green Roof Demonstration Project”, Greening Rooftop for Sustainable Communities Conference, Chicago. Hutchinson, D., Abrams, P., Retzlaff, R. And Liptan, T. (2003) “Stormwater Monitoring Two Ecoroofs in Portland, Oregon, USA”, Greening Rooftops for Sustainable Communities, Chicago, IL. HPO (2007) “Report of the Task Group on Green Roofs and Homeowner Protection in British Columbia to the Homeowner Protection Office Board of Directors”, Homeowners Protection Office, June 22, 2007. URL: http://www.hpo.bc.ca/PDF/Green/GreenRoofReport.pdf Johnston, C., McCreary, K. And Nelms, C. (2004), “Vancouver Public Library Green Roof Monitoring Project”, Greening Rooftop for Sustainable Communities, 2rd annual conference, Portland, OR. Johnston, J. and Newton, J. (1993) “`Building Green, A Guide for Using Plants on Roofs, Walls and Pavements”, The London Ecology Unit, London.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Kongshaung, R. and Bhatt, V. (2004) “The Role of Green Roofs in Cost-Effective City Greening”, Greening Rooftop for Sustainable Communities, 2rd annual conference, Portland, OR. Liptan, T., (2003) “Planning, Zoning and Financial Incentives for Ecoroofs in Portland, Oregon”, Greening Rooftops for Sustainable Communities, Chicago, IL Liu, K.K.Y. and Baskaran, B.A. (2003) "Thermal performance of green roofs through field evaluation," Green Roof Infrastructure Conference, Chicago, IL, (NRCC-46412) URL: http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc46412/ Liu, K.K.Y. (20041) "Sustainable building envelope - garden roof system performance," 2004 RCI Building Envelope Symposium, New Orleans, LA (NRCC-47354) URL: http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc47354/ Liu, K.K.Y. and Baskaran, B.A. (20042) Green Roof Infrastructure - Technology Demonstration, Monitoring and Market Expansion Project, pp. 121, May 15, 2004 (B1054.1) URL: http://irc.nrc-cnrc.gc.ca/pubs/fulltext/b1054.1/ Liu, K.K.Y. and Minor, J. (2005) "Performance evaluation of an extensive green roof," Greening Rooftops for Sustainable Communities, Washington, DC (NRCC-48204) URL: http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48204/ MacMillan, G. (2004) “York University Rooftop Garden Stormwater Quantity and Quality Performance Monitoring Report”, Greening Rooftop for Sustainable Communities, 2rd annual conference, Portland, OR. MacMillan, G. (2006) “Evaluation of an Extensive Green Roof, York University, Toronto, Ontario”, Toronto and Region Conservation. Minke, G. und Witter, G., Haeuser mit Gruenem Pelz, Ein (1982) Handbuch zur Hausbegruenung, Verlag Dieter Fricke GmbH, Frankfurt. Monterusso, M. (2003) “Species Selection and Stormwater Runoff Analysis from Green Roof System”, Master Thesis, Department of Horticulture, Michigan State University Oberndorfer et al. (2007) “Green roofs as urban ecosystems: ecological structures, functions, and services” in Bioscience Magazine, November 1, 2007. Palomo Del Barrio, E. (1998) “Analysis of the Green Roofs Cooling Potential in Buildings”, Energy and Buildings, 27:179-193. Porsche, U. and Kohler, M. (2003) “Life Cycle Costs of Green Roofs – A Comparison of Germany, USA and Brazil”, RIO 3 – World Climate & Energy Event, Rio de Janeiro, Brazil.
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DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009 METRO VANCOUVER
Sailor, D.J. (1995) “Simulated Urban Climate Response to Modification in Surface Albedo and Vegetative Cover”, Journal of Applied Meteorology 34(7) 1694-1704. Schmidt, J. (2008) Personal communication with Joy Schmidt, president of Xero Flor Canada. Tan, P.Y., Wong, N.H., Chen, Y., Ong, C.L., Sia, A. (2003) “Thermal Benefits of Rooftop Gardens in Singapore”, Greening Rooftops for Sustainable Communities, Chicago, IL Taylor, B., Gangnes, D. and Ellison, M. (2005) “Seattle Green Roof Evaluation Project: An Introduction”, Greening Rooftop for Sustainable Communities, 3rd annual conference, Washington, DC. Taylor, B. (2006) “Planning a Green Roof Storm Runoff Monitoring System”, Greening Rooftop for Sustainable Communities, 4th annual conference, Boston. Yok 2005 Yok, T.P., Sia, A., “A Pilot Green Roof Research Project in Singapore”, Green Roofs for Sustainable Communities, Washington, DC, 2005.
8-4
Appendix A
Annotated Bibliography
Appendix A: Annotated Bibliography Author(s) Date
Title
Synopsis This paper discusses the lack of scientific research and critical analysis of the application of eco-roofs in biophysical environments like Vancouvers. It questions many of the potential benefits of green roofs reported in the literature in the Vancouver context, but does agree that green roofs can mitigate urban stormwater runoff. It reviews the variables that affect the stormwater retention, and notes that “an eco-roof used in conjunction with infiltration measures at grade produces a synergistic effect as the roof retains a percentage of the water until the infiltration systems are able to deal with it.” A mesoscale model is used to simulate low-level air temperature in Toronto over 48 hours in late June 2001. Heat island reduction is modelled and the potential role of green roofs is discussed.
–
–
Eco-Roofs and Vancouver: A Critical Analysis. pp 66-92
Bass, B.; Krayenhoff, E.S.; Martilli, A.; Stull, R.B.; and Auld, H.
2003
Beattie, David J.
2004
Brenneisen, S.
2003
The Impact of Green Roofs on Toronto’s Urban Heat Island. Proceedings of Greening Rooftops for Sustainable Communities, Chicago, 2003. 12 pages Green roof research in the USA. Proceedings of International Green Roof Congress, Nürtingen, September 14-15, 2004. pp. 107-110 The Benefits of Biodiversity from Green Roofs – Key Design Consequences. Proceedings of Greening Rooftops for Sustainable Communities, Chicago, 2003. 10 pages
Brenneisen, S.
2003
Bundesverband GartenLandschaftsund
2002
Refugium für Flora und Fauna. Garten + Landschaft 10/2003:26-29. Jahrbuch Dachbegrünung 2002, Thalacker Medien,
Benefit Category or Topic Stormwater management
Urban heat island mitigation
Provides an overview of green roof research and application in the USA, in particular as it differs from that in Germany.
General
A survey of spider and beetle fauna of the new habitats on green roofs in Base, Switzerland revealed numerous endangered species listed in Red Data Books. A study of birds showed systematic use by species of grassland and riverbank habitats. Well designed roof habitats seem to represent a valuable replacement of last land habitat. Structural design of the substrate surface was the most significant factor in supporting biodiversity. The design of green roofs should take into account the wildlife and habitat of the natural surroundings as well as the conditions of the exposed space on top of buildings. Describes a green roof constructed in 1914 near Zurich that supports a variety of orchids and other rare plants.
Urban biodiversity
English title: Green Roof Yearbook 2002. This yearbook contains several articles written by leading green roof researchers. It provides a comprehensive overview of the state of the green roof industry in 2002.
General
Biodiversity
Author(s)
Date
Sportplanzbau e.V. (BGL) Ed.
Title Braunschweig.
Burke, K.
2003
Canadian Mortgage and Housing Corporation (CMHC)
2003
Canadian Mortgage and Housing Corporation (CMHC)
–
Canadian Mortgage and Housing Corporation (CMHC)
–
Davis, K.
2002
Green roofs and regenerative design strategies – the Gap’s 901 Cherry project. Proceedings of Greening Rooftops for Sustainable Communities, Chicago, 2003. 6 pages Fairmount Waterfront Hotel, Vancouver, B.C. – Green Roof Herb Garden Case Study http://www.cmhcschl.gc.ca/en/imquaf/himu/b uin_034.cfm Merchandise Lofts Building Green Roof Case Study http://www.cmhcschl.gc.ca/en/imquaf/himu/b uin_020.cfm Waterfall Building Green Roof Case Study http://www.cmhcschl.gc.ca/en/imquaf/himu/b uin_019.cfm Green Roof Inventory: Preface Report GVRD. 61 pages
Synopsis There are articles about benefits, cost-benefit analysis, policy, design, construction, maintenance, vegetation, and guidelines. Another section lists green roof organizations, research facilities, suppliers and contractors. The paper relates the issues dealt with in designing and building the grass roof at the Gap’s 901 Cherry Avenue office building in San Bruno, California from 1994 to 1997. It focuses on the role of the cost benefit study in the design approval process (e.g., a simply payback of 11 years was estimated), and the benefits of including a native grassland specialist in the design team.
Benefit Category or Topic
Design, policy
A green roof of ivy and pea gravel was initially installed in 1991. The south side of the roof was converted to an herb garden in 1994 for $25,000. The garden measures 2,100 sq.ft. with a soil depth of 18 inches, comprised of 11 beds with amended soils. Values in food production and amenities are discussed.
Urban agriculture & Community enjoyment
Describes a green roof constructed on the Merchandise Lofts Building in Toronto, Ontario, a 12-storey mixed use (condominium, retail, commercial) complex. The green roof, seeded with a prairie meadow mix, is 10,000 sq.ft. surrounded by 15,000 sq.ft. of concrete pavers. Benefits as outdoor recreation area for tenants are discussed. A green roof constructed on the Waterfall Building in Vancouver, B.C. – a mixed office, retail, live-work space building – is described. The roof has both extensive and intensive elements. Benefits of neighborhood beautification, outdoor space, saleability and permitting supports are discussed.
Occupant well being
The report documents over 600 green roofs in the GVRD, the majority of which are garage and building roof decks. The City of Vancouver had the highest number among the municipalities in the Region, and the largest concentration occurred among high-rise residential developments. Ten more detailed case studies are provided. The report provides conclusions on green roof trends, performance, perceptions, and challenges and barriers in the GVRD.
Community benefits, marketability
General
Author(s)
Date
Title
Synopsis
Benefit Category or Topic Thermal insulation
ECOVER website http://www.ecover.com/engli sh/index These 4-3: Gründächer senken die Kosten bei Gespaltener Abwassersatzung. In Proceedings of the EFB-FBB* Gründachsymposium, Ditzingen, March 23, 2003. pp. 31-32
Discusses the green roof on the ECOVER factory in Oostmalle, Belgium built in 1992. Describes the background on stormwater fees in Germany. *EFB-FBB: Europäische Föderation der Bauwerksbegrünungsverbande – Fachvereinigung Bauwerksbegrünung e.V
Incentives – fee reduction
2004
Auswertung der Umfrage Dachbegrünung an Stadtverwaltungen von Städten über 10.000 Einwohner.
Incentives – subsidies, fees
Fachvereinigung Bauwerksbegrünun g e.V. (FBB)
1997
Fischer, P. and Jauch, M
1999
2002
This paper describes the FLL test for determining resistance to root penetration of waterproofing membranes and root barriers. The test is conducted at certain universities around Germany. The title of this paper is, “Drainwater in Potable Water Quality?” It shows how far along the Germans are with their research! Basically, the results of the study were that the drainwater from the tested planting medium does, apart from the colour, meet the standards for drinking water.
Waterproofing
Fischer, P. and Jauch, M.
Verankerung von Dachbegrünung im kommunalen Baurecht durch Festsetzungen im Bebauungsplan oder kommunale Satzungen. Zur Wurzelungsfestigkeit bei Dachbgrünungen. Stadt und Grün 11/1999. pp. 763-768 Dränwasser in Trinkwasserqualität? Dach + Grün 4/2002. pp. 24-31
Survey on green roof policy by the FBB, the main green roof association in Germany, in January 2004. Out of the 1,488 cities contacted, 398 (27%) responded. However, many cities with green roof policies are not represented. The results showed that 70 offer direct financial aid, 201 offer stormwater fee discounts, and 145 have green roof requirements in local development plans. The subsidies are often over 10 €/m² ($16 Cdn) to a stipulated maximum amount. In municipalities with split wastewater fees, green roofs typically earn a discount of between 50 and 100% on the annual stormwater fee. That is an average saving of 0.50 €/m² ($0.80 Cdn) each year for a green roof compared to a conventional roof. Available online from the FBB [www.fbb.de]. This brochure describes how green roofs can be integrated into development regulations.
ECOVER
–
Fabry, Wolfgang
2003
Fachvereinigung Bauwerksbegrünun g e.V. (FBB)
Regulation
Design, stormwater management
Author(s)
Date
Title
Synopsis
Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL)
1998
Bewertung von Dachbegrünung. Empfehlungen sur Bewertung in der Bauleitplanung, bei der Baugenehmigung und bei der Bauabnahme. FLL, Bonn.
Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL) Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL)
2000
Bewertung der wertsteigernden Wirkung von Grünflächen für Immobilien. FLL, Bonn.
Describes the FLL system developed for rating green roof performance in land-use planning, building permit approvals and construction acceptance. The basis of the rating system is the thickness of the green roof construction penetrable by roots, and the ability of the particular roof design meeting minimum requirements for the following parameters: water retention capacity of the growing medium, water retention capacity of the drainage layer, number of plant species for extensive green roofs, and plant biomass for intensive green roofs. The FLL system also identifies qualitative characteristics according to type of roof construction that are used to judge whether a project is suitable for ecological compensation under the Federal Nature Conservation Act. Each natural function parameter is deemed either “possible to fulfill completely”, “possible to fulfill partially”, or “slightly or not possible to fulfill.” The qualitative parameters are: soil, surface water, load shedding from the sewer system, groundwater recharge, purification of stormwater, filtering of air, oxygen production, temperature levelling, flora and fauna habitat, landscape and urban scenery, and people / leisure / healing. English title: Quantification of the Appreciation Effect of Green Spaces on Real Estate Values – referenced in:
2002
Richtlinie für die Planung, Ausführung und Pflege von Dachbegrünungen. FLL, Bonn.
English title: Guidelines for the design, construction and maintenance of roof greening. These are the green roof guidelines “standard” in Germany if not in Europe. Among other items, the document contains tables with runoff coefficients according to roof slope and thickness.
Design
Gedge, D.
2003
“…From Rubble to Redstarts…”. Proceedings of Greening Rooftops for Sustainable Communities, Chicago, 2003. 9 pages
The paper discusses the Black Redstart Action Plan – the Black Redstart being a rare breeding bird in London, England reliant on old vacant lots and brown land. The Action Plan has been a key driving force in establishing green roofs in new urban developments.
Biodiversity
Benefit Category or Topic Performance rating system
Property value
Author(s)
Date
Title
Synopsis
Graham, P. and Kim, M.
2003
A modeling study in the Greater Vancouver Region shows that green roofs are potentially very effective in reducing the volumes and peak rates of runoff from developed areas in the GVR. The results for 50-years watershed retrofit scenarios shows that redevelopment of existing buildings with green roofs could effectively counteract the anticipated effects of climate change and land use densification, and also help to restore watershed health over time.
Hämmerle, Fritz
2002
Henz, Anke
2004
Herman, R.
2003
Hutchinson, D.; Abrams, P.; Retzlaff, R.; and Liptan, T.
2003
Johnston, C.; McCreary, K.; and
2004
Evaluating the Stormwater Management Benefits of Green Roofs through Water Balance Modeling. Proceedings of Greening Rooftops for Sustainable Communities, Chicago, 2003. 9 pages Dachbegrünung rechnen sich. In Jahrbuch Dachbegrünung 2002, Thalacker Medien, Braunschweig. pp. 18-19 Die Bewertung unterschiedlicher Formen der Dachbegrünung nach dem Karlsruher Modell im Rahmen der Eingriffsregelung. In: Proceedings of the EFB-FBB Gründachsymposium, Ditzingen, March 25, 2004. pp. 30-31 Green Roofs in Germany: Yesterday, Today and Tomorrow. Proceedings of Greening Rooftops for Sustainable Communities Symposium, Chicago, 29-30 May 29-30, 2003. 5 pages Stormwater Monitoring Two Ecoroofs in Portland, Oregon, USA. Proceedings of Greening Rooftops for Sustainable Communities, Chicago, 2003. 18 pages Vancouver Public Library Green Roof Monitoring
Benefit Category or Topic Stormwater management
This article gives some values for cost savings.
Design - costs
Describes the performance rating system used by the City or Karlsruhe, Germany in relation to ecological compensation. The model rates how suitable a type of green roof (or other biotope) is for use as an ecological compensation measure based on five natural functions: soil, climate, flora, fauna and water balance. A comparison of performance rating systems by Zeller (2002) found that the Karlsruhe model was the most “well-rounded”.
Performance rating system
Discusses factors in the growth and development of green roofs in Germany.
General
Reports on a monitoring project of an apartment building in Portland, Oregon vegetated with 2 different ecoroofs. Two years of water quality monitoring and 1-year flow monitoring are reviewed. Precipitation retention and peak intensity attenuation are analyzed. Water quality benefits were more difficult to quantify.
Stormwater management
Methods and results of monitoring a 1500 m2 (net area) green roof with 350 mm (14”) soil layer plus vegetation on the Public Library in Vancouver,
Stormwater management
Author(s)
Date
Nelms, C.
Kohler, M.; Schmidt, M.; and Laar, M.
2003
Köhler, Manfred
2004
Kolb, Walter
2000
Kolb, W. and Eppel, J.
2003
Köln, Stadt
2003
Kortright, R.
2001
Title Project. Proceedings of Greening Rooftops for Sustainable Communities, Portland, Oregon, June 2-4 , 2004. 13 pages Green Roofs as a Contribution to Reduce Urban Heat Islands. Proceedings of RIO 3- World Climate & Energy Event, December 1-5, 2003, Rio de Janeiro, Brazil. pp. 493-498 Energetic Effects of Green Roofs on the Urban Climate Near to the Ground and to the Building Surfaces. Proceedings of International Green Roof Congress, Nürtingen, September 14-15, 2004. pp. 72-79 Dachbegrünung wirtschaftlich? Stadt und Grün 4/2000. pp. 224-227 Begrünung von Leichdächern – ein Systemvergleich. Teil 1 – Versuchsergebnisse aus Veithöchheim. Dach + Grün 1/2003. pp. 20-26 Amtsblatt der Stadt Köln. Special Publication Number 58. December 23, 2003. Stadtentwässerungsbetriebe Köln. Evaluating the Potential of Green Roof Agriculture. Research project for
Synopsis
Benefit Category or Topic
B.C. are discussed. Benefits regarding reductions in stormwater volume and peak flows are presented.
The paper discusses the growth in measuring urban heat islands since the late 1970s. A data set of measurements from a gravel roof and two green roofs from July 2003 is used to explain some aspects of surface temperatures in different roof substrates.
Urban heat island Mitigation
Data from the research station in Neubrandenburg, Germany, is provided. Includes information on factors influencing urban climate and factors influencing stormwater retention of green roof systems.
Urban heat island mitigation
Describes a cost-benefit analysis that takes into account the lifespan of the construction, the proportion of runoff, the effect on space conditioning, and the improvement of the living environment. A comparison of six different lightweight green roof systems at a research facility in Veithöchheim. Measurements included weight, water retention, maintenance requirements, vegetation coverage, visual rating, runoff coefficients, and change in finished grade level after 3 growing seasons.
Costs
This is a good example of stormwater fees and how green roofs may qualify for a reduction of these fees. In Cologne, the discount is directly proportional to the runoff coefficient; e.g., a runoff coefficient of 0.9 means 90% of the fee must be paid; a runoff coefficient of 0.3 means only 30% must be paid. The report summarizes the results of a study of a green roof on Trent University’s Environmental Sciences building in Peterborough, Ontario. Fourteen common vegetable crops were planted in a 7.5 x 30 m plot
Incentives - fees
Design
Urban agriculture
Author(s)
Date
Title
Synopsis
Professor Tom Hutchinson, Trent University. http://www.cityfarmer.org/gre enpotential.html
subdivided into four equal beds. Productivity of individual crops and beds, wind speed, soil temperature and moisture were monitored on the rooftop and at ground level. The results were then compared to each other, to the ground level results, and to official Ontario Ministry of Agriculture, Food, and Rural Affairs crop productivity statistics. English title: Extensive Roof Greening: Recommendations and Cost Considerations. This publication contains very detailed information on costs. Chapter A contains recommendations on design and implementation of green roofs. Chapter B is on aspects of stormwater management. Chapter C contains detailed building costs on 10 existing extensive green roofs. Because the costs were difficult to compare, price quotes for a sample green roof project were requested from 50 green roof companies/contractors and these average costs are also provided. In Chapter D, several calculations are shown comparing gravel ballast roofs with extensive green roofs (multi-layer and single layer) over a 40-year lifespan. Some of the factors are whether or not stormwater fees are included and different investment models. Reviews the potential sources of green roof failures, especially those that relate to vegetation, and recommends how to avoid them. Frequent problems cited are: damages to the substrate layer and vegetation caused by wind or water erosion, insufficient initial planting, defects in coverage of the green roof vegetation, pest infestation, waterlogging, imperfection of the substrate layer and the green roof build-up, and poor maintenance. The workshop was designed to provide architects, researchers and policy makers with an introduction to the benefits, development and design of green roofs and an overview of current research projects, needs and opportunities. The project consists of 8 test plots in Portland, Oregon with varying configurations of growth media and drainage. The project is designed to examine propagation methodology, plant material, irrigation regime and maintenance costs of “bare essentials” approaches. The project concluded its first year of results and is intended to continue for the next 4 years.
Krupka, Bernd W.
2001
Extensive Dachbegrünung. Praxisemphelungen und Kostenbetrachtungen. Landesinstitut für Bauwesen des Landes NRW, Aachen.
Krupka, Bernd W.
2004
Potenzielle Fehlerquellen bei Dachbegrünung und deren Vermeidung. Proceedings International Green Roof Congress, Nürtingen, September 14-15, 2004. pp. 136-142
Kuhn, M.; Lui, K.K.Y.; Marshall, S.
2001
Green Roof Infrastructure Workshop Proceedings, June 25, 2001. 34 pages
Lando, P.
2004
Test Plots for a Light Weight, Low-cost, Vegetative Roof in Commercial Applications. Proceedings of Greening Rooftops for Sustainable
Benefit Category or Topic
Design - costs
Design
General
Design testing
Author(s)
Date
Liesecke, HansJoachim
2002
Liesecke, HansJoachim
2003
Lietke, Dirck
2003
Liu, K. and Baskaran, B.
2003
MacMillan, G.
2004
Title Communities, Chicago, 2004. 7 pages Ergebnisse eines Langzeitversuches zur extensiven Dachbegrünung. Teil 1, Dach + Grün 11: 4/2002. pp. 10-17 Ergebnisse eines Langzeitversuches zur extensiven Dachbegrünung. Teil 2, Dach + Grün 12: 1/2003. pp. 4-10 These 4-1: Gründächer sind wirtschaftlich und lassen sich rechnen. In: Proceedings of the EFB-FBB* Gründachsymposium, Ditzingen, March 23, 2003. pp. 29-30 Thermal Performance of Green Roofs through Field Evaluation. Proceedings of Greening Rooftops for Sustainable Communities, Chicago, 2003. 10 pages York University Rooftop Garden Stormwater Quantity and Quality Performance Monitoring Report. Proceedings Greening Rooftops for Sustainable Communities, Portland, Oregon, June 2-4, 2004. 14 pages
Synopsis
Benefit Category or Topic
Results from a long-term study on extensive green roofs. Part 1 provides data on substrate development, thickness, load-bearing capacity and water retention. The paper also discusses the research program.
Stormwater management
Results from a long-term study on extensive green roofs, part 2 provides data on vegetation coverage and vegetation groupings and combinations.
Stormwater management
The author presents cost savings for a green roof on a sample industrial building.
Costs
The National Research Council constructed a field roof facility on its Ottawa campus to measure the thermal performance of a generic extensive green roof with 150 mm of growing medium and a reference (modified bituminous) roof. The green roof reduced temperature and daily temperature fluctuation of the roof membrane significantly in spring and summer, as well as moderated heat flow into the building. The green roof was more effective in reducing heat gain than heat loss. Monitoring results of a green roof on York University’s computer science building in Toronto are presented. The 241 m2 roof garden has a 10% slope and 140 mm substrate. A 131 m2 shingle roof was used as a control. Monitoring occurred from May-November 2003. Reductions in rainfall runoff and peak flows, lag times, and runoff coefficients are discussed.
Thermal insulation/ energy reduction
Stormwater management
Author(s)
Date
Title
Synopsis
Mah, C.
2004
Describes the application of green roofs in the Vancouver area and the recently opened Green Roof Research Facility at BCIT.
Mainz, Christof
2004
BCIT adds momentum to green roof concept. J. Commerce Online, September 27, 2004 issue. 4 pages Förderungen der Dachbegrünung. In: Proceedings of the EFB-FBB Gründachsymposium, Ditzingen, March 25, 2004. pp. 16-17
Discusses the stormwater source control subsidy program in North Rhine, Westphalia.
Incentives – subsidies
Mann, Gunter
1999
2000
This article presents the results of a survey of soil organisms on 125 green roofs. It follows with design recommendations on how to encourage soil fauna. A model is presented for simulating the water balance on green roofs. The model is based on results from the research facility in Krauchenweis, Germany.
Urban biodiversity
Mann, G.; Uhl, M., and Schiedt, L.
Mann, Gunter
2000
Marx, I. and Kolb, W.
2002
Begrünte Dächer als Lebensraum. Stadt und Grün 5/1999. Pp. 328-333 Wasserhaushalt auf begrünten Dächern. Stadt und Grün 4/2000. pp. 246254 Retentionsverhalten begrünter Dächer: In Abhängigketi von der Niederschlagsrevion. Stadt und Grün 10/2000. pp. 681686 Mineralische Zusätze für Einschichtsubstrate in Dachbegrünungen. Dach + Grün 1/2002. pp. 23-28
Benefit Category or Topic General
Stormwater management
There is a table in this article that gives a good overview of the German research into stormwater retention and runoff coefficients for green roofs. Otherwise the article is about a stormwater simulation program.
Stormwater management
This paper describes the testing of different planting medium amendments used to clarify water draining off green roofs. Three amendments are clay, zeolite and activated carbon.
Design, stormwater management.
Author(s)
Date
Title
Maurer, Edmund
2004
McCarthy, S. and McCullough, S.G.
2004
Michels, Kurt
2004
Moran, A.; Hunt, B.; and Jennings, G.
2004
Ngan, Goya
2003
Ngan, Goya
2004
Förderungen von Dachbegrünungen in der Landeshauptstadt Linz (Oberösterreich). In Proceedings of the EFB-FBB Gründachsymposium, Ditzingen, March 25, 2004. pp. 12-15 Milwaukee Metropolitan Sewerage District Extensive Green Roof. Proceedings of Greening Rooftops for Sustainable Communities, Portland, Oregon, June 2-4, 2004. 8 pages Norm- und regelgerechte Abdichtungen für Dächer mit Begrünung. Proceedings International Green Roof Congress, Nürtingen. pp. September 14-15, 2004. pp. 111-118 A North Carolina Field Study to Evaluate Greenroof Runoff Quantity, Runoff Quality and Plant Growth. Proceedings of Greening Rooftops for Sustainable Communities, Portland, Oregon, June 2-4, 2004. 15 pages Green Roof Waterproofing: Expertise from Germany. For Public Works and Government Services Canada. 27 pages Green Roof Policy: Tools for
Synopsis Discusses the green roof subsidy program in Linz, Austria.
Benefit Category or Topic Incentives – subsidies
The MMSD installed the first green roof in the Milwaukee area in July 2003. The primary purpose was to demonstrate the ability of green roofs to reduce stormwater runoff, and to set an example for other public agencies and private owners to install green roof systems. A Green Grid system was used. Stormwater monitoring infrastructure was installed but no data reported as yet.
Stormwater management
Contains information on standards for green roof waterproofing materials. Discusses the different kinds of stresses on waterproofing such as root growth, moisture, mechanical stress, thermal stress, fire prevention and protection against wind uplift. References to German norms, standards and guidelines are provided.
Waterproofing
The results of monitoring two green roofs in North Carolina are presented: Wayne Community College, Goldsboro, NC – flat, one-half (70 m2) with other half as control; 2 soil media depths – 50 mm and 100 mm. Monitored April-December 2003. Neuseway Nature Centre, Kinston, NC – 27 m2 green roof. Monitored July-August and November-December 2003. Rainfall retention, peak flow reduction, and water quality impacts are discussed.
Stormwater management
The report reviews current German methods for waterproofing in green roof design. The German green roof industry has developed detailed standards that serve to reduce the risk of leakage. Problem areas addressed include materials, planning and implementation.
Design
The report – in preparation for the Landscape Architecture Canada
Policy
Author(s)
Date
Title Encouraging Sustainable Design. DRAFT. 56 pages
Oberlander, C.H.; Whitelaw, E.; and Matsuzaki, E.
2002
Optigrün
–
Peck, S. and Kuhn, M.
2003
Peck, S.W.
2002
Roehr, Daniel
2004
Introductory Manual for Greening Roofs. For Public Works and Government Services Canada. 32 pages http://www.optimadachbegruenung.de/rtf_ie/3/ Design Guidelines for Green Roofs. For CMHC and Ontario Association of Architects. 22 pages Green Roofs: Infrastructure for the 21st Century. Prepared for the Clean Air Partnership 1st Annual Urban Heat Island Summit, Toronto, May 2-3, 2002. 16 pages Green roofs – the DaimlerChrysler project, Potsdamerplatz, Berlin, Germany. Proceedings of International Green Roof Congress, Nürtingen, September 14-15, 2004. pp. 143-150
Synopsis Foundation - gives an overview of green roofs and their benefits. There is detailed information on the types of green roof policy in Germany and the legal framework that supports it. Four jurisdictions are selected for more detailed analysis: North Rhine Westphalia, Cologne, Berlin and Linz. The final section contains recommendations on how to develop green roof policy. A manual written as a guide for greening roofs throughout Canada.
Website reports on research at a facility in Tornesch from 1994-1998. The results may also be based on other German research. The article provides an introduction to green roof infrastructure and describes how to implement and market a green roof, examines costs, and presents 3 case studies.
Benefit Category or Topic
Design
Stormwater, thermal insulation Design, costs
This paper introduces green roof technology and describes some of the drivers that will help to create a new niche roofing market. It provides an overview of the latest green roof development work and technical research in Canada, and concludes by describing some of the steps required to turn roofs into a new force for cleaner air, water and cooler more healthy cities.
This case study of the prominent DaimlerChrysler building in Potsdamerplatz, Berlin, contains many valuable insights by the project landscape architect.
Design, construction logistics
Author(s)
Date
Title
Synopsis
Roth-Kleyer, Stephan
2003
Results from experiments in Geisenheim, Germany, comparing 10 different lightweight green roof systems. Some aspects compared were vegetation coverage, aesthetic rating, installation costs and maintenance costs.
Roth-Kleyer, Stephan
2004
Rowe, D.B.; Rugh, C.L.; VanWoert, N.; Monterusso, M.A.; and Russell, D.K.
2003
Schade, Christian
2000
Scholz-Barth, K.
2001
Shirley, C.
2003
Leichtgründach-System im Vergleich. Versuchsergebnisse aus Geisenheim. Dach + Grün 1/2003. pp. 12-19 Wasserrückhalt und Abflussverhalten von Gründächer. Proceedings International Green Roof Congress, Nürtingen, September 14-15, 2004. pp. 80-88 Green roof slope, substrate depth, and vegetation influence runoff. Proceedings of Greening Rooftops for Sustainable Communities, Chicago, 2003. 9 pages Wasserrückhaltung und Abfluβbeiwerte bei dünnschichtigen Extensivbegrünungen. Stadt und Grün 2/2000. pp. 95-100 Green Roofs: Stormwater Management From the Top Down. Environmental Design & Construction JanuaryFebruary 2001: 1-11. http://www.edcmag.com/CD A/ArticleInformation/features/ BNP__Features__Item/0,41 20,18769,00.html The Sustainability Value of the Green Roof as a Water Recycling System (GROW) in Urban Locations.
Benefit Category or Topic Design
Describes the method for measuring runoff coefficients used in the FLL guidelines. Provides results on experiments with varied substrate type, substrate depth and drainage elements. Presents the methodology of measuring with regards to the practical performance and its weak spots.
Stormwater management
The paper reports on 15 simulated rooftop platforms designed to compare the effect of slope (2% and 6.5%) and substrate depth (2.5, 4 and 6 cm) and vegetation (sedum, substrate only and gravel) on runoff. Rainfall retained in the first study examining just slope and depth ranged from 69% (6.5% slope, 4 cm) to 74% (2%, 4 cm). Vegetation of 100% sedum cover retained 66% of rainfall compared to 63% for substrate only and 25% for gravel. The research focuses on stormwater retention and runoff coefficients of thin profile extensive green roofs with slopes of up to 30º.
Stormwater management, design
Stormwater management
The general features and potential benefits of green roofs are discussed.
Stormwater management, thermal insulation/ interior climate control
Discusses the GROW system installed in London, England that recycles grey water from basins, baths and showers through an extended horizontal gravel filter with root zone of plants on the roof.
Water quality
Author(s)
Date
Trautlein, S.
2003
Ulrich, R.S.
1984
Weston Solutions
Zeller, Stefan
2002
Title Proceedings of Greening Rooftops for Sustainable Communities, Chicago, May 29-30, 2003. 9 pages Seeing Green. Metropolis, Tokyo. July 11, 2003. View through a window may influence recovery from surgery. (Abstract) Science 224. pp. 420-421 GreenGrid System – Urban Environment Challenges. http://www.greengridroofs.co m/Pages/Urban.htm Bewertung begrünter Dächer in Bauleitplanung und Eingriffsregelung: Vergleich, Anwendung, Erfolgskontrolle. Diplomthesis, Fachhochschule Nürtingen, Nürtingen, Germany.
Synopsis
Benefit Category or Topic
Discusses the potential application and benefits of green roofs in Tokyo.
General
Views of natural settings and greenery as a patient benefit.
Community benefits
References studies (though does not discuss them in detail) conducted by Weston and at the Lawrence Berkeley National Library regarding potential benefits of green roofs in energy reduction and ambient temperatures.
Thermal insulation & air quality improvement
This thesis examines the different types of green roof performance rating systems used in Germany. In his survey of 355 municipalities, Zeller found that 29 municipalities (8% of responses) used a performance rating system and that there were 24 different types used. The most frequently used system (4 responses) was the one developed by the FLL (1998). It appears that many jurisdictions have devised their own system that may be as simple as a verbal agreement. For reasons of comparability, monitoring, justice and legal conformity, there is motivation to develop a national performance rating system for green roofs.
Incentives/ regulation
Appendix B
Green Roof Design Considerations
APPENDIX B: GREEN ROOF DESIGN CONSIDERATIONS These considerations are based on those presented in the Metro Vancouver Stormwater Source Control Design Guidelines (2005). Extensive green roofs can be one of following designs:
Multiple layer construction (Figure 1A) - consists of either: i) a three-layer system including separate drainage course, filter layer and growing medium or; ii) a two layer system where the growing medium is sized to not require a filter between it and the underlying drainage layer.
Figure 1A: Three-layer construction on inverted roof
Single layer construction (Figure 1B) - consists of a growing medium which includes the filter and drainage functions.
Figure 1B: Single-layer construction on inverted roof
DESIGN CONSIDERATIONS FOR A GREEN ROOF 1. Start the design of the green roof at the same time as the design of the building or retrofit project, so that the structural load of the green roof can be balanced with the structural design of the building. From the outset, involve all design disciplines – structural, mechanical and electrical engineers, architects and landscape architects – and include roofing design professionals in a collaborative and optimization effort (Oberlander et al., 2002). 2. Provide construction and maintenance access to extensive green roofs. Access through a ‘man door’ is preferable to access through a small roof hatch (Peck & Kuhn, 2001). Provide areas of storage for maintenance equipment. Review Workers Compensation Board requirements for safety of maintenance workers – can gardeners working near the edge of the roof use the same harness fastenings as window washers (Oberlander et al., 2002)? Provide a hose bib for manual watering during establishment if no automatic irrigation system is planned.
3. Roofs with less that 2% slope require special drainage construction so that no part of the growing medium is continuously saturated. As the slope increases, so does the rate of rainfall leaving the roof. This can be compensated for by using a medium with high water storage capacity. Roofs with over 20º require special precautions against sliding and shearing (FLL. 2002). If inverted roof systems are used with exterior insulation, good drainage needs to be provided to prevent continuous saturation of the insulation, and subsequent damage (Peck & Kuhn, 2001). With inverted roofs, the green roof components must allow moisture to move upwards from the insulation and to eventually evaporate (Krupka, 1992). 4. Provide plant free zones to facilitate access for inspections and maintenance and prevent plants from spreading moisture onto exposed structural components. They can also function as a measure against fire and wind-uplift. They should be at least 50 cm wide and located along the perimeter, all adjacent facades and covered expansion joints, and around each roof penetration. 5. Fire breaks of non-combustible material, such as gravel or concrete pavers, 50 cm wide, should be located every 40 m in all directions, and at all roof perimeter and roof penetrations (FLL, 2002). Other fire control options include use of sedums or other succulent plants that have a high water content, or a sprinkler irrigation system connected to the fire alarm (Peck & Kuhn, 2001). 6. There are several choices of waterproof membranes. Thermoplastic membranes, such as PVC (polyvinyl choride) or TPO (thermal polyolefin) using hot air fusion methods are commonly used for green roof applications. Elastomeric membranes like EPDM Newly planted extensive green roof (ethylene-propylene rubber materials) have high tensile showing plant-free zones at drain strength and are well-suited to large roof surfaces with and edges – White Rock Operations fewer roof penetrations. Modified bitumen sheets are Building Credit: Lanarc Consultants Ltd. usually applied in two layers and are commonly available. Liquid-applied membranes are generally applied in two liquid layers with reinforcement in between. The quality is variable. A factor in choosing a waterproofing system is resistance to root penetration (see 7). 7. Provide protection against root penetration of the waterproof membrane by either adding a root barrier or using a membrane that is itself resistant to root penetration (more cost efficient). Resistance to root penetration is not being tested in Canada at time of writing1. Thermoplastic and elastomeric membranes in suitable thicknesses are usually resistant to root penetration. Roofing membranes, existing or new, which contain bitumen or other organic materials are susceptible to root penetration and micro-organic activity. These types of roofing membranes need to 1
Check with the manufacturer to determine if the membrane is resistant to root penetration according to the German FLL Root Penetration Test, 2002.
be separated from the growing medium by a continuous root barrier unless they contain an adequate root repelling chemical or copper foil (Ngan, 2003). 8. Chemically incompatible materials such as bitumen and PVC require a separation layer (FLL, 2002). 9. When the roofing membrane installation is complete, but prior to installing layers above the waterproof membrane, it should be tested by flooding and thorough inspection. Any leaks should be repaired prior to installing materials above the membrane (Ngan, 2003). 10. Install a protection layer to protect the waterproof membrane/root barrier from physical damage caused by construction activities, sharp drainage materials such as lava rock or broken expanded clay, and subsequent levels of stress placed on the roof (Ngan, 2003). 11. The drainage layer may be drain rock, but is often a lightweight composite such as lava, expanded clay pellets, expanded slate or crushed brick. If weight is a concern, rigid plastic materials that allow rapid lateral drainage may be used. The drainage layer may also function to store water and make it available to the vegetation during dry periods. The top of the drainage layer should always be separated from growing medium by filter cloth. 12. Light weight growing medium is often a combination of sand, pumice or other lightweight absorbent filler, and a small amount of organic matter. The FLL has guidelines about the properties of these manufactured soils which are too detailed to list completely. Some of the important values for multiple layer construction are as follows (FLL, 2002):
grain size distribution: silt (d ≤ 0.063 mm) ≤ 15 % mass (see Figure 11);
content of organic substance: 8% mass (with apparent density ≥ 0.8 g/cm³ in dry condition), 6% mass (with apparent density < 0.8 g/cm³ in dry condition);
infiltration rate: ≥ 0.6 mm/min;
maximum water capacity: ≥ 10% volume;
pH value: 6.5-8.0;
carbon content: ≤ 25; and
salt content (water extract): ≤ 3.5. Extensive green roof on a sloping residential roof, Germany Credit: Goya Ngan
Figure 11: Grain size distribution range for substrates used in multiple layer extensive green roofs (FLL, 1995: 34)
13. In calculating structural loads, always design for the saturated weight of each material (Oberlander et al., 2002). See Section 2.6 for weights of common building materials. 14. Light weight growing medium can be subject to wind erosion when dry. If planting is delayed through a dry weather season, provide a wind erosion control blanket over the growing medium. 15. The drainage layer may be drain rock, but is often a lightweight composite such as lava, expanded clay pellets, expanded slate or crushed brick. If weight is a concern, rigid plastic materials that allow rapid lateral drainage may be used. The drainage layer may also function to store water and make it available to the vegetation during dry periods. The top of the drainage layer should always be separated from growing medium by filter cloth. 16. Plant choices for extensive green roofs are limited to plants that can withstand the extremes of temperature, wind, and moisture condition on a roof. Typically, extensive green roofs use a variety of mosses, sedums, sempervivums, alliums, other bulbs and herbs, and grasses. 17. Avoid specifying or allowing volunteer plant materials with aggressive root systems (e.g. bamboo, couch grass, tree seedlings). Supply and install growing medium that is free of weeds (Ngan, 2003). 18. Design planting to respect microclimate and sun/aspect conditions. Collaborate with mechanical engineers on placement of exhaust vents, and design plantings accordingly (Oberlander et al., 2002).
19. Avoid swaths of one species. The chances of creating a self-maintaining plant community are increased when a wide mix of species is used. 20. Planting methods include seeding, hydroseeding, spreading of sedum sprigs, planting of plugs or container plants, and installing pre-cultivated vegetation mats. 21. If automatic irrigation is required, low volume and rainwater reuse systems are preferred. 22. Provide intensive maintenance for the first two years after the plant installation – including watering in dry periods, removal of weeds, light fertilization with slow release complete fertilizers, and replacement of dead plants. It is recommended that the maintenance contract for the first 3-5 years be awarded to the same company that installed the green roof and that the service be included in the original bid price (Peck & Kuhn, 2001). Once established, a typical extensive green roof should require only one or two annual visits for weeding of undesired plants, clearing of plant-free zones and inspecting of drains and the membrane. 23. Installers should have experience with green roof systems. It may be preferable to have one company handle the entire project from roofing to planting to avoid scheduling conflicts and damage claims (Peck & Kuhn, 2001). If this is not possible, make a clear separation between the responsibilities of the roofing contractor and those of the green roof contractor (Krupka, 1992). 24. Although green roof membranes will last longer than others, leaks can still occur at flashings or through faulty workmanship. Some companies are recommending an electronic leak detection system to pinpoint the exact location of water leaks, thus allowing easy repair (Peck & Kuhn, 2001). 25. Consider the environmental impact of each green roof material. How much energy was required to extract, manufacture and deliver the material? Is there a suitable material derived from local recycled products? What effect does the material have on water quality? How often must it be replaced? How will it be disposed of? Is it recyclable? 26. Several companies provide Metro Vancouver with complete green roof service, and offer a range of long-term guarantees on the entire assembly. This type of comprehensive installation may be more expensive than comparable ‘off the shelf’ products not specifically designed for green roof use. The decision on risk management is with the owner (Peck & Kuhn, 2001). GREEN ROOF STRUCTURAL CONSIDERATIONS A green roof has weight implications on the structure below it. The significance of this structural load in terms of structural design and costs depends on the weight of the proposed green roof, and the location of heavier areas (e.g. deeper soils depths for larger plants) in relation to columns and other structural bearing members.
In general:
Extensive green roof has lower structural implications that intensive green roof, due to the lower depth of growing medium and related weight.
Concrete structures often are capable of handling the structural loads of extensive green roof without significant additional expense.
Lightweight wood and/or steel buildings with large spans (e.g., industrial/ commercial warehousing or retail) may be restricted in their ability to support green roof loads. In these cases, designers should consider very lightweight green roof components (e.g. 75 mm lightweight growing medium) to minimize structural consequences.
The stormwater effectiveness of green roofs is in direct proportion to the water storage capacity of its growing medium and plants. Generally, deeper growing medium depths provide higher stormwater storage capacities. In the Metro Vancouver climate, growing medium depths may need to approach 300mm in wetter parts of the region to meet 100% of rainwater capture targets and thus to avoid the need for off-roof stormwater source control. However, successful designs using wood/steel lightweight structures will balance a certain amount of on-roof rainwater capture with green roofs with a companion role for at-grade stormwater source control.
Placing heavier structural loads (e.g. deeper soil for trees or larger plants) over columns rather than mid-span can reduce the need for structure.
Use of lightweight filler material (e.g. Expanded Polystryrene (EPS) under a minimum depth of growing medium is a common technique used in Intensive Green Roof projects to create berms or other grading infills without significant structural load, as compared to similar grading using soil materials.
In calculating structural loads, always design for the saturated weight of each material (Oberlander et al., 2002). See Table 2-1 for weights of common building materials.
Table 2-1: Weights of Common Building Materials (Oberlander et al., 2002: 26) Material Kg/m3 Light weight concrete 1,298-1,622 Precast concrete 2,108 Reinforced concrete 2,433 Gravel 1,946 Timber – hardwood (av.) 730 Timber –softwood (av.) 568 Sand (dry) 1,460-1,784 Sand (wet) 1,784-2,108 Water 1,013 884-1121 Light-weight growing medium (moist condition)
All green roof projects require the services of an experienced structural engineer.
Appendix C
Summary of Business Case Research
Appendix C: Business Case Analysis – Reference Documents Benefit Reference Case Study (Building/Location) Johnston, C., McCreary, K., and Vancouver Public Library, Stormwater Nelms, C. 2004. Vancouver Vancouver, B.C. – 1,500 m2 (net Management Public Library Green Roof area) green roof with 350 mm Monitoring Project. Proceedings (14”) soil layer plus vegetation Greening Rooftops for green roof. Sustainable Communities, Portland, Oregon, June 2-4, 2004. 13 p.
Moran, A., Hunt, B., and Jennings, G. 2004. A North Carolina Field Study to Evaluate Greenroof Runoff Quantity, Runoff Quality and Plant Growth. Proceedings Greening Rooftops for Sustainable Communities, Portland, Oregon, June 2-4, 2004. 15 p.
MacMillan, G.. 2004. York University Rooftop Garden Stormwater Quantity and Quality Performance Monitoring Report. Proceedings Greening Rooftops for Sustainable Communities, Portland, Oregon, June 2-4, 2004. 14 p.
Wayne Community College, Goldsboro, NC – flat, one-half (70 m2) with other half as control; 2 soil media depths – 50 mm and 100 mm. Monitored AprilDecember 2003. Neuseway Nature Centre, Kinston, NC – 27 m2 greenroof. Monitored July-Aug, Nov-Dec 2003. York University computer science building, Toronto – 241 m2 roof garden with 10% slope and 131 m2 shingle (control) roof. 140 mm substrate. Monitored MayNovember 2003.
Quantified Indicator Measured stormwater runoff: 16% reduction in volume compared to estimated runoff for a traditional (torch-on membrane) flat roof. Compared to 33% maximum possible reduction (natural, predevelopment conditions), this represented a 48% reduction in available runoff volume. Peak flow reduction: Summer: >80% reduction. Winter: ~30% in small winter events, mean annual rainfall or >2-year storm). Rainfall retained (volume temporarily stored and then lost due to evapotranspiration): Goldsboro – 62% Kinston – 63% Reduction in peak rainfall: Goldsboro – 78% Kinston – 87% Water quality – TN (total nitrogen), TP (total phosphorous) concentrations: Both significantly higher in greenroof runoff than in rainfall, hypothesized to be leaching from the soil media, which is composed of 15% compost (high N and P). Reduction in total runoff volume/ m2: Average – 55%. Spring/summer – 76%. Fall (Sept.-Nov.) – 37%.* Reduction in peak flow rates: Up to 85% for storm events < 20 mm. 82% for storm events 20-29 mm. 68% for storm events 30-39 mm. 46% for storm events > 40 mm. Lag time (centre of rainfall mass to peak): Garden: range 3-89 minutes. Control: range 0-4.5 minutes. Runoff coefficient (ratio runoff to precipitation): Garden: range 0-1 (Nov*). Control: range 0.8-1.2.
Benefit
Reference
Case Study (Building/Location)
Quantified Indicator *Reduced performance suggested being a result of cooler temperatures, plant die off, irrigation, and decreased evapotranspiration rates.
Hutchinson, D., Abrams, P. Retzlaff, R., Liptan, T. 2003. Stormwater Monitoring Two Ecoroofs in Portland, Oregon, USA. Proceedings of Greening Rooftops for Sustainable Communities, Chicago 2003. 18 p FLL. 2002. Richtlinie für die Planung, Ausführung und Pflege von Dachbegrünungen. Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL), Bonn.
Apartment building in Portland, Oregon vegetated with 2 different ecoroofs. Two years of water quality monitoring and 1 year flow monitoring.
Precipitation retention: 69% for 4-5” substrate section. Nearly all rainfall absorbed during dry period storms. Water quality benefits more difficult to quantify.
*These coefficients are based on a rainfall event of 300 L/(s x ha) on a previously saturated roof left to drain for 24 hours.
Runoff coefficients for roof slope up to 15º * >50 cm thickness: C=0.1 >25-50 cm thickness: C=0.2 >15-25 cm thickness: C=0.3 >10-15 cm thickness: C=0.4 >6-10 cm thickness: C=0.5 >4-6 cm thickness: C=0.6 >2-4 cm thickness: C=0.7 (roof with membrane: C=1.0, gravel roof: C=.8)
**These values are based on a location with 650-800 mm of annual precipitation and multiyear records. In regions with less precipitation, the retention capacity is higher and in regions with higher precipitation, it is lower.
Runoff coefficients for roof slope over 15º * >10-15 cm thickness: C=0.5 >6-10 cm thickness: C=0.6 >4-6 cm thickness: C=0.7 >2-4 cm thickness: C=0.8 Average annual water retention capacity (%) and the annual runoff coefficient/permeability factor (C)** extensive 2-4 cm: 40%, C = .60 extensive >4-6 cm: 45%, C = .55 extensive >6-10cm: 50%, C = .50 extensive >10-15 cm: 55%, C = .45 extensive >15-20 cm: 60%, C = .40 intensive 15-25 cm: 60%, C = .40 intensive >25-50 cm: 70%, C = .30 intensive >50 cm: >90%, C = .10
Benefit
Reference Stadtentwässerungsbetriebe Köln. Available from www.stadtentwaesserungsbetrieb e-koeln.de
Case Study (Building/Location) Cologne
Quantified Indicator The stormwater fee for Cologne is 1.10 €/m²/yr ($1.80). Green roofs are eligible for a discount. The discount is proportional to the runoff coefficient. For example, if a green roof has a runoff coefficient of 0.3, the owner pays 30% of the annual fee. If the green roof has only a runoff coefficient of .7, then the owner pays 70% of the fee.
Optigrün. http://www.optimadachbegruenung.de/rtf_ie/3/
Research took place at a facility in Tornesch from 1994-1998. The rainfall is approximately 900 mm. May also be based on other German research.
Comparison of average stormwater retention for various Optima green roof systems with different thicknesses. 5 cm gravel: 25% 8 cm extensive: 50% 12 cm extensive: 60% 35 cm intensive: 85% Regardless of type of greening and thickness, green roofs retain at least half of the precipitation and release it by evapotranspiration. Comparison of the maximum peak flow (after a heavy rainfall event or continuous rain) for different types of construction. 5 cm gravel: 112 l/(s x ha) 8 cm extensive: 47 l/(s x ha) 12 cm extensive: 22 l/(s x ha) 35 cm intensive: 26 l/(s x ha)
Thermal Insulation/ Reduction in Energy Consumption
Liu, K. and Baskaran, B. 2003. Thermal Performance of Green Roofs through Field Evaluation. Proc. Greening Rooftops for Sustainable Communities, Chicago 2003. 10 p.
Field roof facility on National Research Council building, Ottawa, Ontario - constructed to measure the thermal performance of a generic extensive green roof with 150 mm of growing medium and a reference (modified bituminous) roof.
Greenroofs.com http://www.greenroofs.com/world _extensive_cases.htm Ecover website http://www.ecover.com/english/in dex.htm
ECOVER factory, Oostmalle, Belgium, 1992. Manufacturer of biodegradable laundry and other green produces. 5,000 m2 (2 acre) roof of meadow grasses, sloped, extra insulation layer of perlite. Roof is mowed twice per
Roof temperature modification: the exposed membrane of the reference roof reached over 70º C while the green roof membrane rarely reached over 30º C. The median daily temperature fluctuation of the reference roof membrane was 45º C; of the green roof - 6º C. Heat flow reduction: Green roof reduced average daily energy demand for space conditioning from 6-7.5 kWh/day to less than 1.5 kWh/day, a more than 75% reduction. Not quantified - From Ecover website: “The first ecological airconditioner – The grass roof plays an important role in managing the factory's temperature. During the summer the grass roof absorbs some of the sun's heat, which means that it remains pleasantly cool in the factory. At night, moisture settles on the grass. The dampening process ensures cooling the following morning. And during the winter, the covering on the roof reduces the air circulation
Benefit
Reference
Case Study (Building/Location) year and weeded as necessary. Pacific Telephone and Telegraph (PT&T) building, Sacramento, CA
Quantified Indicator which increases the temperature in the factory.” Not quantified. “Pacific Telephone and Telegraph (PT&T) in Sacramento, CA, for instance, constructed a half-acre roof garden on its building in 1962. The constant indoor air environment provided by the green roof helps protect the company's sensitive telephone computer equipment, which requires a perfectly humidified environment.”
Weston Solutions. GreenGrid System – Urban Environment Challenges. http://www.greengridroofs.com/Pa ges/Urban.htm
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Optigrün. http://www.optimadachbegruenung.de/rtf_ie/3/
Research took place at a facility in Tornesch from 1994-1998. The rainfall is approximately 900 mm. May also be based on other German research.
“In a recent study, WESTON estimated that greening the rooftops of all city buildings in Chicago would result in nearly $100 million of annual energy savings. Peak demand would be cut by 720 megawatts – the equivalent of several coal-fired generating units or one small nuclear power plant.” “According to the Lawrence Berkeley National Laboratory (LBNL), reducing the ambient temperature in a city by three degrees has the equivalent air quality impact of converting all of the city’s cars to electric power. Computer modeling conducted by LBNL scientists indicates that widespread heat-reduction measures, such as planting rooftop vegetation, could easily lower a city’s temperature by five degrees.” Maximum temperature under the green roof 5 cm gravel: 50º C 8 cm extensive: 43º C 12 cm extensive: 29º C 35 cm intensive: 23º C
Scholz-Barth, K. 2001. Green Roofs: Stormwater Management From the Top Down. Environmental Design & Construction Jan-Feb. 2001: 111. http://www.edcmag.com/CDA/Arti cleInformation/features/BNP__Fe atures__Item/0,4120,18769,00.ht ml
Minimum temperature under the green roof 5 cm gravel: -21º C 8 cm extensive: -18º C 12 cm extensive: -12º C 35 cm intensive: 0º C Sound Insulation
Benefit Roof Membrane Protection
Reference Optigrün. http://www.optimadachbegruenung.de/rtf_ie/3/
Case Study (Building/Location)
Quantified Indicator Comparison of a gravel ballast roof with an extensive green roof over 40 years (1,000 m²). 5 cm gravel roof requires a partial renovation after about 20 years. The cost would be 28,000 € ($44,800) 10 cm extensive green roof does not require renovation in the time period The cost of the membrane is estimated at 55 €/m² ($88). With roof greening there is a cost saving of 60% (33 €/m² ($53)) because of longer life span of the membrane from 25 years to 40 years. Roof greening protects against damage and therefore green roofs require fewer repairs. Cost savings estimated at 4 €/m² ($6.4).
Private roof terrace, Omate, Italy. 1994.
Not quantified. Owner converted unused space (60 m2) over double garage into garden for entertaining, relaxation and gardening. ZinCo Floradrain FD 60 used. Not quantified. Outdoor recreational space for future tenants. “While originally the roof was to be comprised of container gardens, the green roof’s low weight allowed for the design of additional green space without creating the need to re-examine and make adjustments to the loading capacity of the roof.”
Hämmerle, Fritz. Dachbegrünung rechnen sich. In BGL (Bundesverband Garten-, Landschafts- und Sportplanzbau e.V.), Ed. 2002. Jahrbuch Dachbegrünung 2002, Thalacker Medien, Braunschweig. pp. 1819.
Operation & Maintenance Occupant Well-Being/ Productivity
(indirect)
Greenroofs.com http://www.greenroofs.com/world _intensive_cases.htm Canadian Mortgage and Housing Corporation (CMHC). Merchandise Lofts Building Green Roof Case Study http://www.cmhcschl.gc.ca/en/imquaf/himu/buin_0 20.cfm Ulrich, R.S. 1984. View through a window may influence recovery from surgery. (Abstract) Science 224: 420-421.
Merchandise Lofts Building, Toronto, Ontario – 12-storey mixed use (condominium, retail, commercial) complex. Green roof (prairie meadow mix) of 10,000 sq.ft. surrounded by 15,000 sq.ft. of concrete pavers. Suburban Pennsylvania hospital
“Records on recovery after cholecystectomy of patients in a suburban Pennsylvania hospital between 1972 and 1981 were examined to determine whether assignment to a room with a window view of a natural setting might have restorative influences. Twenty-three surgical patients assigned to rooms with windows looking out on a natural scene had shorter postoperative hospital stays, received fewer negative evaluative comments in nurses' notes, and took fewer potent analgesics than 23 matched patients in similar rooms with windows facing a brick building wall.”
Benefit Surrounding community enjoyment, psychologicall y pleasing environment
Reference Canadian Mortgage and Housing Corporation (CMHC). Green Roof Herb Garden Case Study http://www.cmhcschl.gc.ca/en/imquaf/himu/buin_0 34.cfm
Case Study (Building/Location) Fairmount Waterfront Hotel, Vancouver, B.C. A green roof of ivy and pea gravel was initially installed in 1991. The south side of the roof was converted to a herb garden in 1994 for $25,000. The garden measures 2,100 sq.ft. with a soil depth of 18 inches, comprised of 11 beds with amended soils. Waterfall Building, Vancouver, B.C. Mixed use (office, retail, live-work space) building. Green roof, visible to the public, was seen as a beautification of the area. Both extensive and intensive elements.
Quantified Indicator Not quantified. Hotel guests enjoy the garden and other terrace amenities. Occupants of neighbouring buildings also benefit from the view.
Bass, B., Krayenhoff, E.S., Martilli, A., Stull, R.B., and Auld, H. 2003. The Impact of Green Roofs on Toronto’s Urban Heat Island. Proc. Greening Rooftops for Sustainable Communities, Chicago 2003. 12 p. Trautlein, Steve. 2003. Seeing Green. Metropolis, Tokyo. July 11, 2003.
A mesoscale model is used to simulate low-level air temperature in Toronto over 48 hours in late June 2001.
Modeled temperatures indicate an urban heat island of 2-3o C. Irrigation in the city reduces modeled temperatures by 1o C, while adding a small amount of irrigated green roof coverage deepens and extends this cooling over a larger area of the city. Modeled cooling may be artificially low due to model assumptions, case study choice, and input data of unknown quality.
Tokyo
“The Tokyo-based Organization for Landscape and Urban Greenery Technology Development estimates that if half of the roofs in the city were planted with gardens, daytime high temperatures in summer would fall by .84º C, which would save ¥110 million ($126 million Cdn.) on air conditioning costs daily.”
Canadian Mortgage and Housing
Fairmount Waterfront Hotel,
Canadian Mortgage and Housing Corporation (CMHC). Waterfall Building Green Roof Case Study http://www.cmhcschl.gc.ca/en/imquaf/himu/buin_0 19.cfm
Urban Heat Island Effect Mitigation
Not quantified. Additional useable space for residents: increased sale-ability; and assisted in getting approval from the City Planning Dept., particularly in getting relaxation of height limit.
Air Quality Improvement Green House Gases & CO2 Sequestration Urban
Annual food production, primarily herbs, saves the hotel
Benefit Agriculture
Reference Corporation (CMHC). 2003. Green Roof Herb Garden Case Study http://www.cmhcschl.gc.ca/en/imquaf/himu/buin_0 34.cfm
Kortright, R. 2001. Evaluating the Potential of Green Roof Agriculture. Research project for Professor Tom Hutchinson, Trent University. http://www.cityfarmer.org/greenpo tential.html
Case Study (Building/Location) Vancouver, B.C. A green roof of ivy and pea gravel was initially installed in 1991. The south side of the roof was converted to an herb garden in 1994 for $25,000. The garden measures 2,100 sq.ft. with a soil depth of 18 inches, comprised of 11 beds with amended soils. Green roof on Trent University Environmental Sciences building, Peterborough, Ontario. 14 common vegetable crops planted in a 7.5 x 30 m plot, subdivided into four equal beds. Productivity of individual crops and beds monitored separately. Wind speed, soil temperature and moisture were monitored on the rooftop and at ground level. The results were then compared to each other, to the ground level results, and to official Ontario Ministry of Agriculture, Food, and Rural Affairs crop productivity statistics.
Urban Recreational Areas
Greenroofs.com http://www.greenroofs.com/world _intensive_cases.htm
The Company Group Gegenbauer Golf Course, Berlin. Built in 1996.
1,400 m2 roof turned into a miniature golf course; owner is an avid golfer. ZinCo Interational’s Floradrain FD 25 and FD 60 used. FD 60 is strong enough to support heavy lawn mowers. Extremely high maintenance to keep playing field at optimum level.
Urban Biodiversity
Brenneisen, S. 2003. The Benefits of Biodiversity from Green Roofs – Key Design Consequences. Proceedings of Greening Rooftops for Sustainable Communities, Chicago 2003. 10 p.
Local biodiversity recorded on 16 green roofs in Base, Switzerland for 3-year period:
Quantified Indicator estimated $25,000-30,000/year. Hotel guests enjoy the garden and other terrace amenities. Occupants of neighbouring buildings also benefit from the view.
“From my results it was not possible to conclude that green rooftop food production can serve as a viable agricultural alternative in any broad commercial sense. However, it can be concluded that, on a green roof such as the one considered here, rooftop growing conditions are not substantially different from those on the ground. Therefore, it is possible to conclude that such a development is possible on a small scale, given experience and a broader incorporation of green roofs such as this one into the urban landscape.”
78 spider species, 14 classified as “faunistically interesting”: range 7-27 species. 254 beetle species, 27 listed in Red Data Books, range 15-79 species. 12 species of birds recorded foraging, resting, singing, preening. Most frequent species were ones that occur in open landscapes (mountain areas, river banks, steppes); few sightings of birds
Benefit
Reduced Demand & Deferred Investment in Infrastructure Financial Benefits & Savings Marketability & Valuation
Reference
Case Study (Building/Location)
Quantified Indicator common to urban areas. Structural design of the substrate surface was most significant factor in supporting biodiversity.
Appendix D
®
Green Roofs and LEED
APPENDIX D
DESIGN CONSIDERATIONS FOR THE IMPLEMENTATION OF GREEN ROOFS APRIL 2009
METRO VANCOUVER
What is LEED®? The LEED (Leadership in Energy and Environmental Design) Green Building Rating System® is a voluntary, consensus-based national standard for developing high-performance, sustainable buildings. LEED® design adds value to buildings and reduces the total cost of ownership. LEED® was created by building industry leaders, with the mandate to:
define "green building" by establishing a common standard of measurement; promote integrated, whole-building design practices; recognize environmental leadership in the building industry; stimulate green competition; raise consumer awareness of green building benefits; and transform the building market.
How Is Certification and Accreditation Achieved? The U.S. and Canadian Green Building Councils have developed rating systems for buildings, and exams for building professionals. LEED® building certification can be achieved in the following six categories: 1. 2. 3. 4. 5. 6.
New Commercial Construction and Major Renovation Projects (LEED-NC). Existing Building Operations (LEED-EB). Commercial Interiors Projects (LEED-CI). Core And Shell Projects (LEED-CS). Homes (LEED-H). Neighbourhood Development (LEED-ND)
Green buildings may achieve “Certified”, “Silver”, “Gold” or “Platinum” LEED® certification by accumulating a minimum of 26 and a maximum of 70 points, in six categories:
Sustainable Sites; Water Efficiency; Energy & Atmosphere; Materials & Resources; Indoor Environmental Quality; and Innovation & Design Process.
Green Roofs and LEED® Installation of a green roof can aid in fulfilling the requirements to obtain points associated with 11 LEED® credits. Points for four of these credits are obtainable solely or primarily by constructing a green roof with a minimum area. For the remaining credits, a green roof will facilitate fulfilling requirements that are based on other design strategies. Table D-1 lists the LEED® credits which are relevant to green roofs.
Table D-1: LEED® Credits which are Relevant to Green Roofs Indicates that a LEED® credit may be achieved solely or primarily by the green roof component of the building. Green Text No Shading Indicates that constructing a green roof will facilitate obtaining a LEED® credit that is based on other strategies.
Credit Site Credit 5.1 – Reduced Site Disturbance, Protect or Restore Open Space
Site Credit 6.1 – Stormwater Management, Rate and Quantity
Site Credit 6.2 – Stormwater Management, Treatment
Site Credit 7.2 – Heat Island Effect, Roof
Requirement
On greenfield sites, limit site disturbance including earthwork and clearing of vegetation to 12 metres (40 feet) beyond the building perimeter, 1.5 metres (5 feet) beyond primary roadway curbs, walkways, and main utility branch trenches, and 7.5 metres (25 feet) beyond constructed areas with permeable surfaces (such as pervious paving areas, stormwater detention facilities and playing fields) that require additional staging areas in order to limit compaction in the constructed area;
OR On previously developed sites, restore a minimum of 50% of the site area (excluding the building footprint) by replacing impervious surfaces with native or adapted vegetation. If existing imperviousness is less than or equal to 50%, implement a stormwater management plan that prevents the post-development 1.5 year, 24 hour peak discharge rate from exceeding the pre-development 1.5 year, 24 hour peak discharge rate; OR If existing imperviousness is greater than 50%, implement a stormwater management plan that results in a 25% decrease in the rate and quantity of stormwater runoff. Construct site stormwater treatment systems designed to remove 80% of the average annual post-development total suspended solids (TSS) and 40% of the average annual postdevelopment total phosphorous (TP) based on the average annual loadings from all storms less than or equal to the 2-year/ 24-hour storm. Do so by implementing Best Management Practices (BMPs) outlined in Chapter 4, Part 2 (Urban Runoff), of the United States Environmental Protection Agency’s (EPA’s) Guidance Specifying Management Measures for Sources of Nonpoint Pollution in /Coastal Waters (Document No. EPA-840-b-93-001C January 1993) or the local government’s BMP document (whichever is more stringent). Use ENERGY STAR roof-compliant, high-reflectance AND high emissivity roofing (for low slope roofs: initial reflectance of at least 0.65 and three-year-aged reflectance of at least 0.5 when tested in accordance with ASTM E903 and emissivity of at least 0.9 when tested in accordance with ASTM 408; for steep slope roofs: initial reflectance of at least 0.25 and three-year-aged reflectance of at least 0.15 when tested in accordance with ASTM E903 and emissivity of at least 0.9 when tested in accordance with ASTM 408) for a minimum of 75% of the roof surface; OR Install an extensive or intensive “green” (vegetated) roof for at least 50% of the roof area. Combinations of high albedo and vegetated roof can be used providing they collectively cover 75% of the roof area.
Points
1
1
1
1
Credit Water Credit 1.1 – Water Efficient Landscaping, Reduce By 50%
Water Credit 1.2 – Water Efficient Landscaping, No Potable Use or No Irrigation Energy Credit 1 – Optimize Energy Performance
Materials Credit 4.1 – Recycled Content, 7.5% (Post-Consumer + ½ Post-Industrial) Materials Credit 4.2 – Recycled Content, 15% (Post-Consumer + ½ Post-Industrial) Materials Credit 5.1 – 10% Extracted and Manufactured Regionally Materials Credit 5.2 – 50% Extracted and Manufactured Regionally
Requirement Use high-efficiency irrigation technology; OR Use captured rain or recycled site water to reduce potable water consumption for irrigation by 50% over conventional means. Use only captured rain or recycled site water to eliminate all potable water use for site irrigation (except for initial watering to establish plants), OR do not install permanent landscape irrigation systems.
1
1
Reduce design energy cost compared to the energy cost budget for energy systems regulated by ASHRAE/IESNA Standard 90.1-1999 (without amendments), as demonstrated by a whole building simulation using the Energy Cost Budget Method described in Section 11 of the Standard;
OR Reduce the greenhouse gas emissions due to the energy consumption by regulated loads of the Proposed design, as compared to that of a baseline Reference model, by using whole building computer energy modelling. Use materials with recycled content such that the sum of post-consumer recycled content plus one-half of the post-industrial content constitutes at least 5% of the total value of the materials in the project.
Points
Use materials with recycled content such that the sum of post-consumer recycled content plus one-half of the post-industrial content constitutes at least 10% of the total value of the materials in the project. Use a minimum of 20% of building materials and products that are manufactured within a radius of 800 km (500 miles) if transported by truck OR within a radius of 3,500 km (2,200 miles) if transported by rail. Of these regionally manufactured materials, use a minimum of 50% of building materials and products that are extracted, harvested or recovered (as well as manufactured) within a radius of 800 km (500 miles) if transported by truck OR within a radius of 3,500 km (2,200 miles) if transported by rail.
1-10
1
1
1
1
Appendix E
Resources
APPENDIX E: GREEN ROOF RESOURCES Scientific & Technical Resources BCIT Centre for Architectural Ecology – Collaborations in Green Roofs and Living Walls http://commons.bcit.ca/greenroof/ National Research Council of Canada – Institute for Research in Construction – Sustainability of Green Roof Technology Project http://irc.nrc-cnrc.gc.ca/bes/prsi/greenroof_e.html Green Skins Lab, University of British Columbia School of Architecture and Landscape Architecture www.greenskinslab.sala.ubc.ca/ Michigan State University Green Roof Research Program http://www.hrt.msu.edu/greenroof/ Penn State Center for Green Roof Research http://web.me.com/rdberghage/Centerforgreenroof/Home.html Colorado State University Green Roof Program http://greenroof.agsci.colostate.edu/ The Ladybird Johnson Wildflower Center at the University of Texas at Austin http://www.wildflower.org/greenroof/ Water Environment Research Foundation – Sustainable Stormwater http://www.werf.org/livablecommunities/ American Society of Landscape Architects Green Roof Demonstration Project http://land.asla.org/050205/greenroofcentral.html The Green Roof Centre of Excellence, Neubrandenburg, Germany http://www.gruendach-mv.de/en/index.htm World Green Roof Infrastructure Network http://www.worldgreenroof.org/index.html Green Roofs for Healthy Cities – Green Roof Infrastructure Industry Association http://www.greenroofs.org/ Greenroofs.com - The Green Roof Industry Resource Portal http://www.greenroofs.com/
Insurance Concerns British Columbia Homeowner Protection Office (HPO) http://www.hpo.bc.ca/About/Initiatives/GreenRoofs.php
Green Roof Product Suppliers
Soprema – Sopranature Green Roof System http://www.soprema.ca/en/content/10/sopranature.aspx Xeroflor Canada Ltd. http://www.xeroflor.ca/ American Hydrotech – Waterproofing and Garden Roof Assembly http://www.hydrotechusa.com/garden-roof.htm ELT Easy Green – Green Roof Systems http://www.eltgreenroofs.com/index.php Natvik Ecological Professional Services (Guelph, Ontario) http://www.roofgarden.ca/index.php?view=pageView&pageid=235
Government Resources Toronto and Region Conservation Authority - For the Living City http://www.trca.on.ca/Website/TRCA/website.nsf/WebPage/trca__living_city__living_city?OpenDocumen t&ppos=1&spos=0&rsn= City of Toronto Green Roofs Pilot Program http://www.toronto.ca/greenroofs/incentiveprogram.htm City of Seattle, Washington, City Green Building Program – Green Roofs http://www.seattle.gov/DPD/GreenBuilding/OurProgram/Resources/TechnicalBriefs/DPDS_009485.asp City of Portland, Oregon, Sustainable Stormwater Management Program – Eco-Roofs http://www.portlandonline.com/BES/index.cfm?c=44422& City of Chicago, Illinois, Department of Environment – Green Roofs http://egov.cityofchicago.org/city/webportal/portalDeptCategoryAction.do?BV_SessionID=@@@@00608 79241.1227634544@@@@&BV_EngineID=ccceadefkjdhgfjcefecelldffhdfhk.0&deptCategoryOID=536889313&contentType=COC_EDITORIAL&topChannelName=Dept&entityName=Environment&dept MainCategoryOID=-536887205
Green Roof Design Guidelines and Standards Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL) – German Green Roof Design Guidelines http://www.f-l-l.de/english.html Introductory Manual for Greening Roofs – Oberlander, Whitelaw and Matsuzaki, 2002 (Public Works and Government Services Canada http://www.bluestem.ca/pdf/PWGSC_GreeningRoofs_wLink_3.pdf Design Guidelines for Green Roof – Peck and Kuhn, 2003 (Ontario Association of Architects and CMHC) http://www.cityofchicago.org/webportal/COCWebPortal/COC_ATTACH/design_guidelines_for_green_ro ofs.pdf ASTM Subcommittee on Sustainability – including work item under development: Guide for Green Roof Systems http://www.astm.org/COMMIT/SUBCOMMIT/E0671.htm
BuildSmart is the Lower Mainland’s resource for sustainable design and construction information. Developed by Metro Vancouver, this innovative program encourages the use of green building strategies and technologies; supports green building efforts by offering tools and technical resources; and educates the building industry on sustainable design and building practices. www.metrovancouver.org/ buildsmart
Kerr Wood Leidal Associates Limited has developed this publication under contract to Metro Vancouver to assist design professionals, builders and owners with making informed decisions when pursuing or planning for green roof installations.
The project team is a collaboration of professionals who work in the fields of green building and green roof engineering, stormwater management, Leadership in Energy and Environmental Design® (LEED®) certification, landscape architecture, planning and environmental design. The project team is drawn from the following firms: 1) Kerr Wood Leidal Associates Ltd.(KWL), engineering consultant; 2) HB Lanarc Consultants Ltd., environmental planners and landscape architects; 3) Goya Ngan, international researcher and landscape architect; 4) Glotman Simpson, structural engineer; and 5) Karen K.Y. Liu, PhD, green roof expert with XeroFlor International. The report was authored by Chris Johnston of KWL, with support from Alexandra Johnson and Laurel Morgan. Dr. Karen Liu from XeroFlor International provided comments on the text and contributed valuable information on recent research and improvements in green roof technology for the final report. Additional editing, comments and contributions to the final report were made by several persons including Lyn Ross, Vaillant Tang, Christine Cummings, Robert Hicks and Mark Wellman at Metro Vancouver, Maureen Connelly at British Columbia Institute of Technology and Steven Peck at Green Roofs for Healthy Cities as outside reviewers.
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