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Thermal bridging analysis to improve Part L performance offers a highly cost-effective way to improve building quality and achieve carbon dioxide reduction targets.

Carrying out the analysis should be considered for all construction types being assessed under Part L 2013, even if bespoke calculations are required to ascertain accurate linear thermal transmittance values (psi-values).

Our analysis has indicated that, for a typical block of 50 flats, switching from default thermal bridging assumptions in SAP calculations is the equivalent of increasing wall insulation performance from 0.26W/m2K to 0.16W/m2K (approximately 60mm additional rigid insulation).

The total cost of finite element analysis to determine 10 psi-values is approximately £5,000. The cost of increasing insulation performance to achieve the same modelled performance improvement could be as much as £25,000 for 50 flats meaning a potential saving of £20,000 by simply investing in detailed analysis at an early stage. The savings for larger schemes will be proportionally larger.

There are multiple additional benefits of carrying out thermal bridging analysis over simply increasing insulation thicknesses. The key area for improvement is overall building quality – analysis will improve the understanding of cold bridging in the building and help to identify and eliminate the risk of surface condensation at cold spots.  The insulation thickness increase that we modelled would also require wall thickness to increase by approximately 60mm, taking up valuable floor space.

We advise early consideration at planning stage to optimise the thermal performance of construction details.