Glossary

A wall with inner and outer masonry layers (eg block or brick), with a cavity in between. The cavity serves as a way to drain water out of the wall. Cavities can be insulated to improve their ability to keep heat in the building, but it's important to use moisture-resistant materials like polystyrene bead for cavity insulation, particularly in wet areas.

See combined heat and power (CHP)

The BRE's environmental assessment tool for dwellings. As with BREEAM, buildings are assessed on their overall environmental performance, resulting in six levels of scoring.

This measures the energy efficiency of certain heating and cooling appliances, such as heat pumps. COP is the ratio of useful energy output (heating or cooling) to the amount of energy put in, so a heat pump with a COP of 4 puts out four times as much energy as it uses. The higher the COP, the more efficient the device.

See 'combined heat and power'

See 'thermal bridging'

A technology that generates both heat and electricity from the same plant. Also known as cogeneration

A condensing boiler can re-capture some of the heat normally released in the form of hot gases, and use it to heat up water returning from your central heating system. This means that it requires less energy to produce a given amount of heat, and is therefore more efficient.