What is Wall-To-floor Ratio

What is Wall-to-Floor Ratio? The wall-to-floor ratio of a building is calculated by dividing the external wall area by the gross internal floor area. This indicates the proportion of proportion  of external wall required to enclose a given floor area.  A reasonable reasonable ratio ratio on central central London London offices is considered considered to be in the order of 0.40, 0.40, with 0.3 0.3 and below being regarded as very efficient and significant articulation or indentation ca!able of !ushing it over 0.0. The si"!le illustrations below give basic indications of how varying storey height and height  and perimeter length #driven length  #driven by the shape of shape of the building and the articulation  of the fa$ade% with the same floor area, area, can affect the ratio.

‘Standard’

Floor Area: 100m Wall Area: !0m Wall-to-Floor Ratio: 0"!0

#eight

Floor Area: 100m Wall Area: $0m Wall-to-Floor Ratio: 0"$0

Shape

Floor Area: 100m Wall Area: %0m Wall-to-Floor Ratio: 0"%0

Articulation

Floor Area: 100m Wall Area: %&m Wall-to-Floor Ratio: 0"%&

&t is worth noting that a circular !lan is the "ost efficient sha!e in ter"s of wall to floor ratio as indicated below'

Floor Area: 100m Wall Area: '%m Wall-to-Floor Ratio: 0"'% (owever, in very few cases is this the "ost econo"ical !lan sha!e of a building, as the cost of constructing a circular as a!!osed to a straight envelo!e is generally greater than the saving in quantity of the envelo!e. )e!ending on the building use it can also i"!act on internal s!ace !lanning !otentially "a*ing it "ore difficult and less efficient.

#o( is (all-to-floor ratio measured? +hilst the ratio is a si"!le calculation, it does give rise to the i"!ortant questions of what should be included in the "easure"ents of external wall area and gross internal floor area for  this !ur!ose. &t is i"!ortant that this is done consistently to ensure co"!arisons of different buildings are accurate. The following is a si"!listic guide covering what should and should not be included. &t is a "easure of e)ternal walls only and should not include atriu" walls. Therefore if the following is a si"!le floor !lan with a central enclosed atriu" #si"ilar to idity lace% the red line re!resents the walls to be included and the corres!onding floor area is as shaded.

(owever, if there is a central light well with no roof and the walls therefore being external, then that should be included in the calculation. This is diagra""atically re!resented in !lan as follows'

The efficiency #in ter"s of wall-to-floor ratio% of different !arts of the building should be considered and !resented se!arately. /oof !lant and base"ent areas, for exa"!le, can distort the efficiency of the "ain fa$ade and floor !lates. A si"!le section re!resenting the areas that should be included in the calculation for the "ain fa$ade is as follows'

Why is Wall-to-Floor Ratio *mportant?  As stated in the foreword to this docu"ent the external fa$ade re!resents one of the 1ig Three2 cost ele"ents in any new office develo!"ent, ty!ically   56 of the overall shell and core construction cost. As the !revious exa"!les illustrate it is obvious that, assu"ing a constant fa$ade cost !er " 5, the ele"ental cost will increase when the wall-to-floor ratio increases. This is si"!ly because there is a greater fa$ade area !er " 5 gross internal floor area.  As an exa"!le an increase in the wall-to-floor ratio fro" 0.40 to 0.4 on a 500,000 sqft 7&A building with a fa$ade costing 8900 !er " 5 could result in an increase in the total shell and core cost of a!!roxi"ately 56. This is detailed below' •

500,000 sqft 7&A : ;,;0" 5

•

Total shell and core cost, say 500,000sqft x 8