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
Green oak

Green oak is oak that was felled within the last 18 months. Because it is still drying, it has a high moisture content. But according to Oakwrights it is stronger, more durable and easier to work with than dried oak, as well as being less expensive.


Wastewater from baths, sinks, dishwashers, washing machines etc - essentially all a house's wastewater except that from toilets and macerators/food grinders

ground granulated blastfurnace slag

A steel-industry by-product that is used instead of traditional portland cement for 'eco' and 'green' cements and concretes. Because GGBS is essentially a by-product of an existing industry, it's considered to have a much lower embodied energy than portland cement

ground source heat pump

Heat pump that uses the ground - which has a fairly consistent temperature - as a heat source. Ground source heat pumps take heat from the ground and deliver it to internal spaces, using electricity to boost the temperature if needed