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Geberit Pluvia Roof Drainage System Emergency Drainage for Flat Roof and Gutter Constructions

Autumn 2001

Pluvia Roof Drainage System Basic information on emergency drainages

Emergency Drainage Each flat roof or separate flat roof section and each gutter must be equipped with appropriate emergency overflows, irrespective of the number of outlets. This requirement has been defined in the following standards and regulations: • SN 592 000 • VDI 3806 • DIN 19 599 • DIN EN 12056-3 • DIN 1986-100 • Guidelines for flat roofs issued by the German Roofers' Trade Association • Avis Techniques CSTB • SSIV Guidelines for gutter dimensioning Therefore, the drainage type (negative pressure system or conventional roof drainage system), has no influence on the basic question whether emergency overflows should be provided. Further reasons for the construction of emergency drainage systems, especially for negative pressure roof drainage systems, are the following: • Dimensioning of the negative pressure system does not take into account any country-specific calculation principles of the downstream non-pressure drainage. Therefore, if the non-pressure drainage has smaller dimensions, the discharge capacity might be reduced. • As regular cleaning of the city-sewer cannot be controlled, obstructions might lead to rainwater backing up into the roof drainage system. • Trapezoidal roof constructions are increasingly being designed for smaller static loads. Therefore, the danger of collapse due to record precipitations and of water penetrating into the building is high.

Arrangement of the emergency overflows on the flat roof

When emergency overflows are positioned on a roof with a Pluvia roof drainage system, the following measures must be taken into account: • Emergency overflows must be positioned in such a way that they do not obstruct the rainwater flow between the outlet and the emergency overflow. • The weir must be placed 5 cm above the rainwater outlet, regardless of the type of emergency overflow used (this also applies to roofs with vegetation). It must be ensured that there are no flat roof edges or roof entryways, etc. below the emergency overflow level.

Autumn 2001, GIAG / Hun

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Pluvia Roof Drainage System

Emergency Drainage • The emergency overflow should always be constructed through the roof balustrade, if possible. If the roof construction does not allow an unobstructed emergency overflow through the balustrade, emergency drainage can also be via another piping system. This piping system should, however, not be directed to the same city-sewer as the Pluvia system. It is even better to route this piping system above the ambient level.

• External emergency overflows should have a square design; this ensures a faster operating behaviour than a system with round apertures. Emergency overflows using another piping system may, however, also be round (with pipes). In this case, the inlet funnel should preferably have a round design too.

Dimensioning of emergency overflows on the flat roof

An infinite number of country-specific guidelines and calculation procedures is available for the dimensioning of emergency overflows. Regardless of these procedures and taking into account record precipitations and the gravitational constant etc., Geberit offers an easy way to calculate the dimensions of emergency overflows by using the company's empirical values. Total amount of rainfall in litres / s x 25 cm2 Example: Roof area with four outlets à 8 l / s = 32 l / s x 25 cm2 = 800 cm2 In order to guarantee that this emergency overflow will respond as quickly as possible to the respective amount of water and that the roof will not become overloaded, the horizontal aperture of the emergency overflow should be large. This means the height of the aperture should range from 10 to a maximum of 15 cm. The overall size of the emergency overflow aperture in the above example would then be 80 x 10 cm or 54 x 15 cm. The total aperture size can, of course, also be divided into several smaller apertures. These dimensions can also be used for an internal emergency drainage system (e.g. a pipe system). According to the above example, approx. two PE pipes of 250 mm should be used to guarantee sufficient emergency drainage.

Autumn 2001, GIAG / Hun

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Pluvia Roof Drainage System

Emergency Drainage This dimensioning method ensures an efficient roof drainage even if outlets are blocked or the city-sewer is obstructed. Record precipitations (~ rainfall intensity twice as high as normal ) can thus be handled. Double rainfall intensity corresponds to a safety factor of 2.0. An even higher safety factor must be applied to buildings requiring higher protection (hospitals, theatres,…). (For detailed information, see EN 12056-3 chap. 4.2.)

H var.

10-15

5

10-15

Emergency overflow via balustrade (square)

5

Internal emergency overflow (round)

Arrangement of emergency overflows in the gutter

For gutter constructions, the appropriate arrangement of emergency overflows is equally important. This especially applies to internal gutters (shed-type gutters): For this gutter type, emergency overflows can only be positioned at the two front ends of the gutter. For bracket mounted gutters, the emergency overflows can be positioned near the outlets (lowest point of the corresponding gutter section) as well as at the front ends. To guarantee efficient emergency overflows in accordance with the following dimensioning, the basic specifications on the use of the Pluvia system for gutters must be considered: • Maximum distance of outlets 20 m, • Minimum gutter width 35 cm, • Gutter slope in the longitudinal direction 5 mm / m (0.5 %).

0.5 % max.10 m

max. 20 m

Arrangement of outlets in gutters

Autumn 2001, GIAG / Hun

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0.5 % max. 20 m

Pluvia Roof Drainage System

Emergency Drainage min. 35 cm min. + 0.0 %

Cross-section of external gutters with minimum requirements

For the dimensioning of emergency overflows for gutter constructions, the two different arrangements must be considered. Dimensioning of emergency overflows placed alongside the gutter

For emergency overflows fixed alongside the gutter, dimensioning is basically the same as for flat roof emergency overflows. The only difference is that for gutter contructions the weir must be placed 10 cm above the outlet. Total amount of rainfall in litres / s x 25 cm2 The required aperture surface that has been calculated must be distributed equally among the number of outlets.

H 10 - 15 cm 10 cm

var.

Emergency overflow for gutters, longitudinal arrangement

Example: Gutter with four outlets of 6 l / s = 24 l / s x 25 cm2 = 600 cm2 For an aperture height of 10 cm the total aperture length is 60 cm. Total aperture length 60 cm : 4 outlets = 15 cm; i.e. the ideal emergency overflow aperture for each outlet is 15 x 10 cm.

Dimensioning of emergency overflows placed at the front end of the gutter

Autumn 2001, GIAG / Hun

Notwithstanding any existing calculation tables and the abovementioned basics on dimensioning, the following can be said when calculating the front end emergency overflow aperture: • Both front ends of the gutter must be equipped with an emergency overflow aperture. • These apertures must be mounted in such a way that the whole gutter width is covered; the top must be kept open.

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Pluvia Roof Drainage System

Emergency drainage • The weir must be mounted at least 5 cm and maximum 10 cm above the following outlet aperture (depending on the distance between the outlet and the front end or the longitudinal slope).

0.5 %

5 - 10 cm

max. 10 m Emergency overflow for gutters, front end arrangement

G. width 5 - 10 cm Cross-section of emergency overflow for gutters, front end arrangement

The correct dimensioning of the gutter in accordance with the country-specific standards and guidelines is the prerequisite for these emergency overflows to be able to meet the requirements. The minimum requirements of a gutter can also be determined using the chart below (if the volume flow is known). Gutter width in cm 100 75

60 56

50

52 48 44

40

40 36

35

32

Volume flow VGutter in l/s

28 24 20 16 12 8 4 10 15 20 Gutter depth in cm Autumn 2001, GIAG / Hun

6

25

30

35

40

Pluvia Roof Drainage System Cleaning of the system and maintenance

Autumn 2001, GIAG / Hun

Emergency Drainage Flat roofs and gutters require regular maintenance. For example, any contamination and vegetation must be removed and leaves cleared away regularly in order to avoid having blocked drains. This cleaning work should be undertaken more or less frequently depending on the specific ambient conditions. The work should include cleaning the Pluvia rainwater outlets as well as the emergency overflows. In order to clean the Pluvia rainwater outlets, it is necessary to briefly remove the cover and the inlet disk and also clean the dirt off the inlet element underneath. The frequency of cleaning has to be defined for the building by its owner who can entrust this task to a suitable person such as the caretaker.

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