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Options for Thermal Bridging

23 Aug 2021


Architects know that a well-insulated dwelling is key to achieving low emission rates on new build developments. High specification windows and thick quantities of insulation in the walls, floors and roofs means less heat can escape from the building, reducing energy demand and lowering fuel bills.

Taking consideration of heat loss through Thermal Bridging is just as important, but this is often overlooked by designers.

This is where heat from a building escapes through corners and joints; Wherever there’s a break in the insulation layer, you’ll find a thermal bridge.

The majority of smaller housebuilders in the country follow a guidance manual called Accredited Construction Details (ACD). This is a standardised set of best practice building techniques to reduce heat loss through a building’s thermal breaks.

But ACDs were drawn up twenty years ago, and building techniques have moved on.

When Approved Document Part L changes next year, the option to use ACDs in SAP calculations is being removed. This means that, from next year, designers will need to find alternative ways of limiting heat loss through the thermal bridges in their developments.


So, what are the alternatives?

Option 1 is ignore them, but that’s not going to be viable. A dwelling that needs to comply with the new energy and emission targets won’t get anywhere near compliance if default thermal bridging assumptions are used.

Option 2 is to use Government Approved Details. This is a new online library of junctions which is being created by the Building Research Establishment (BRE). Just like the old ACD library, the junctions are standardised and free for anyone to use. We expect most smaller housebuilders will take this option because it’s free, although the improvements in SAP won’t be anything special.

Option 3 is to use manufacturer supplied data. Many insulation, lintel and balcony providers have produced their own thermal bridging calculations specific to their products. If your company buys products directly from the manufacturer, ask if they have psi-value or thermal bridging calculations available. This approach usually gives a boost to the performance of SAP calculations.

Finally, option 4 is go bespoke. Larger housebuilders already take this approach, and we’re expecting many more construction companies to follow when the targets change. Once a developer has commissioned their own psi-value calculations, the same results can be used on all future construction sites, providing their specification doesn’t change. The initial cost of the calculations makes sense when you can show improvements on hundreds of SAP results for years to come.


Reducing heat loss through Thermal Bridging will be an essential puzzle piece when complying with the Future Homes Standard targets. But it’s not the only puzzle piece, and high efficiency standards will be required across the specification to meet overall compliance.

For more information about thermal bridging bespoke psi-values, SAP10 and the new Part L targets, contact Energist today.

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Jon Ponting

Energy & Sustainability Specialist


Jon Ponting

Energy & Sustainability Specialist
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