Jobs under L12021 will no longer be able to use standard ACD details, we can supply bespoke PSI details to your construction requirements. We can provide PSI detail services, please email for more information.
What Are PSI Values And Why Do They Matter?
PSI values measure the rate of heat loss where building elements join - for example, where a wall meets a floor or a roof connects to a gable end. These junctions, known as thermal bridges, are often weak spots in the building fabric. If not properly detailed, they can lead to heat loss, condensation, and increased energy bills. Bespoke PSI values give you an accurate picture of how your design performs at these key junctions.
The Move Away From Default Values
With the latest updates to Building Regulations, relying on default Accredited Construction Details (ACDs) is no longer enough. Using default PSI values can significantly raise your SAP score, making it harder to meet compliance targets under Part L. Bespoke PSI calculations help bring your energy assessment figures down, meaning you can reduce insulation thickness or other costly upgrades elsewhere in the build.
Fully Modelled To Match Your Construction
We create junction models based on your exact construction details. That includes wall build-up, insulation types, fixing methods, and structural materials. Our calculations are carried out using approved thermal modelling software, in line with BR 497 and other relevant standards. This gives you results you can rely on, helping to improve SAP performance and reduce thermal bridging.
Better Accuracy, Better Performance
By using PSI values tailored to your project, you get a more accurate energy assessment. This helps you identify where improvements can be made and avoid over-specifying in other areas. It also supports a smoother path through building control by showing that your project has been properly assessed. Better thermal detailing results in fewer cold spots, less chance of mould, and a more comfortable indoor environment.
Integrated With Your SAP Assessment
As part of our wider energy assessment services, we can integrate your bespoke PSI values directly into your SAP calculations. This ensures consistency across all performance modelling and helps avoid delays later on. If needed, we can also work with your Architect or Contractor to adjust construction details for better thermal results. Our goal is to help you meet compliance with practical, buildable solutions.