Perplexed by all this talk of u-values and blower door tests? Our sustainable building glossary will help you get to grips with the key terminology.

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Term Definition
Fabric first

Fabric First, the principle of designing a building fabric that keeps in heat — through a well insulated, airtight structure that is free of thermal bridges — before thinking about ‘bolt-on’ technologies like renewable energy.

Form factor

Form factor is the ratio of a building’s total surface area (the walls, roof and ground floor) to its treated floor area. The smaller the form factor, the more efficient the shape of the building and the less surface area from which heat can escape. A form factor of under 3.0 is considered ideal for a passive house.


A chemical sometimes found in building products. Classified as a 'known human carcinogen' by the UN International Agency for Research on Cancer

FSC certified wood

The Forest Stewardship Council is a non-profit group that certifies forests that are managed sustainably