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

Thermal resistance or R-value is a measure of a material's ability to resist heat flow. A high R-value is desirable when choosing insulation for your home. R-values are commonly quoted in North America, whereas U-values are used more often in Europe. A U-value of 0.27W/m2K equates to an R-value of 21, while a U-value of 0.15 W/m2K equates to an r-value of 38. See U-value for more information

Relative humidity

This is the amount of water vapour in the air relative to the amount the air can hold at the current temperature. Healthy relative humidity is generally regarded as being between 40% and 60%. High relative humidity can lead to condensation, dampness and mould.