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
embodied energy

Energy required to extract, manufacture process, transport, and install a product


This is the Passive House Institute's standard for retrofit projects. It demands airtightness of 1.0 air changes per hour and space heating demand of 25kWh/m2/yr (as opposed to 0.6 air changes per hour and 15 kWh/m2/yr for the original passive house standard).

Exhaust air heat pump

This type of heat pump extracts heat from waste air leaving a heating system and uses it to provide hot water or space heating, using electricity to boost the temperature if needed.

expanded polystyrene

A type of rigid foam used for insulation, typically for external insulation

External insulation

Insulation applied to the outside of a building