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 bridging

A thermal bridge occurs when heat or cold transfers across an external surface of a building. This can cause heat to escape from the building or cold to enter. Thermal bridging occurs when a thermally conductive material (ie a material with low resistance to heat flow) can penetrate or bypass the insulation layer. For example, insulation is often placed between timber joists in roofs, however the joists themselves may conduct heat and reduce the effectiveness of the insulation by acting as a thermal bridge along which heat can be transferred out and lost. Thermal bridging can greatly reduce the effectiveness of insulation, so it's crucial to minimise thermal bridges during the design of a new build or refurbishment.

Synonyms - Thermal bridges
thermal bypass

On this one we?ll defer to Mark Siddall, writing here for "Thermal bypass is heat transfer that bypasses the conductive or conductive-radiative heat transfer between two regions. Defined in this manner thermal bypass includes convective loops, air infiltration and wind washing. In this context [...] it should be recognised that the term thermal bypass is being applied to largely unfamiliar, and often unregulated, heat transfer. Furthermore it is an acknowledgement that air movement can lead to a significant increase in the heat loss when compared to predicted values. This means that even when the architect, and builder, thinks that a design has addressed the performance requirement it is very likely that it has not."

You have been warned...

thermal mass

The capacity of a building material to store heat. Materials with a high thermal mass absorb heat, store it and then release it later on. This can help to smooth out extremes in temperature inside a building, helping to maintain a comfortable internal environment and reduce the need for heating. Heavyweight construction materials like concrete and bricks have more thermal mass than lightweight materials like timber. Thermal mass is particularly important in climates where there is a large difference between daytime and night-time temperatures, which isn't the case in the temperate Irish climate, though thermal mass can still be beneficial in Irish building - it's of most benefit when buildings are well insulated and occupied consistently throughout the day.

Thermostatic radiator valves

Self-regulating valves, typically attached to radiators or other water heating systems, used to control the room temperature automatically based on what temperature the TRVs are set at