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Thermal Bridging

In these areas it’s usual for builders to put extra insulation in these junctions to avoid cold spots. If the builder does this in line with Accredited Construction Details (ACD) guidance, it can make big improvements to the SAP assessment – typically 10-15%. – So it’s definitely worth looking into.

At this point it’s worth noting that this is not the same as the more well known Robust Details which deals with acoustics and sound-proofing rather than thermal efficiencies.

Download the drawing packs..

If you’re new to this, the first thing we recommend you do is download the drawing packs from the Planning Portal website.

There are different ones for cavity walls, timber frames etc. You may find you’re already building to these standards and don’t even realise it! Each of these junctions has a reference number in the bottom left corner (for example, MCF-GF-01 shows how you can minimize heat loss where your cavity wall meets the ground floor).

The heat loss is measured as a psi-value (or ?–value) – the lower the psi-value of a junction, the better it will perform. There are around twenty different types of junction that the SAP assessment takes into consideration.

Accredited Construction Details

For calculating the SAP assessment, if you tell us which ACD junctions you’re building to, we can use these lower psi-values in the calculation and you’ll likely end up with a lower emission rate overall and possibly even a higher EPC rating.

These ACDs are not the only way of improving your SAP assessment through better thermal bridging; there are also Enhanced Construction Details available which will give you even better psi-values, and many manufacturers publish their own values, especially with pre-built timber frame constructions.

It is also possible to have bespoke psi-values calculated, however this is the more expensive option and is currently not a common approach.

As thermal bridging makes such a large difference to your SAP assessments, we always recommend that default psi-values are not used and that builders follow the guidance of Accredited Construction Details or a similar scheme.

This usually only applies to new buildings, however you’ll notice there is also guidance in the ACD drawings packs showing how you can lower the risk of cold spots with existing solid walls.

Jon Ponting

Author: Jon Ponting

This article was published by Jon Ponting on 25.01.2013.