Thermal Bridging - The Important Facts

What is thermal bridging?

Thermal bridging is the term used to define the heat loss through junctions in a building fabric, which is expressed as a liner thermal transmittance value (Ψ-value [Psi]). “Junctions” could include wall-roof and wall-floor junctions, party walls, corners, sills, jambs, lintels, and any other significant junctions of the building fabric. Ψ-values can then be used to arrive at a Y-value: a factor, which allows the calculation of the building’s overall heat loss through thermal bridges. 

Heat loss through thermal bridging is now found to be very significant. Currently you have the option to use accredited construction details (ACD), or have the thermal junctions of a house modelled or use a default figure.

What does this mean to me?

With the new Part L 2012, we would definitely advise the use the Accredited Construction Details (ACD) as a minimum or use the energy saving trusts Enhanced Construction Details (ECD) to help achieve a DER/TER pass.  If they are not used then the Dwelling Emission Rate will increase and this alone can be enough to Fail Building Regulations.

How best to achieve building regulations?

Using ACDs or ECDs will provide a specific detail for all the main construction methods together with a detail for each junction, e.g. what to do between each element, detailing how to insulate the junction, ensure an appropriate air seal and how best to avoid thermal bridges.

How to evidence for an EPC?

If you are using ACD's, you will be required to evidence this to the energy/SAP assessor upon completion. How best to achieve this is to sign, date and complete each sheet as the works proceed for the relevant junctions on your project. The following links will direct you to the planning portal where you can download all the junctions types.

For more information visit:-

Accredited Construction Detail (ACD)