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Figure 3.20 Form Factor and building type
from Sustainable Design
by generaskopje
Recommendations are given for Surface to Volume Ratio for a typical single family house to be between 0.8 – 1.0, while others recommend it to be below ≤ 0.8 or even 0.517 .
Form factor
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The Form Factor (F) is another useful parameter which describes the relationship between the external surface area (A) and the internal Net Floor Area (NFA). This allows useful comparisons of the efficiency of the building form relative to the useful floor area.
F= A/NFA (m2/m2)
Sustainable buildings should aim to achieve Form Factor value of three or less. If the form factor is over three, achieving the criteria of the Passivhaus Standard becomes challenging. It is can be difficult to achieve a form factor below 2.5 on a stand-alone residential building. However, taller buildings, can more easily achieve a form factor lower than 118 .
Figure 3.20Form Factor and building type
Also, the complexity of the form can have an impact on increasing the thermal bridges which needed to be solved with the architectural design and increasing the shading- factors that can have an impact on the annual energy balance.
Another aspect to bear in mind is that the change of the shape of the building and its Form Factor influences the occurrence of thermal bridges. Buildings with higher Form Factor have more thermal bridging which needs to be solved by appropriate detailing.
17 https://www.forum-holzbau.com/pdf/ihf09_Lylykangas.pdf 18 https://www.greenspec.co.uk/building-design/heat-loss-form-factor/
