Thermal bridging is an area of a building which has a significantly higher heat transfer due to either a break in insulation or reduced insulation. This would be around openings or where two elements meet i.e. floor to wall, wall to roof etc. When completing a SAP calculation we need to account for thermal bridging due to the heat loss and therefore reduced energy performance of the dwelling. The heat loss associated with these thermal bridges is expressed as a linear thermal transmittance (Ψ-value) – pronounced as ‘psi-value’ Below you can see the thermal bridges that need to be accounted for
In general, we tend to follow Accredited Construction Details (ACDs) although some insulation companies have their own standard details which can have better psi values. Another area you could look at is by using thermally insulated lintels which significantly reduces the heat transfer through that junction.
Instructing a SAP Assessor at design stage is imperative and can save time and money in the log run.
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