PSI-Value Calculations

What is a PSI Value calculation?

The PSI value calculation is a technique used to assess the heat loss or gain at junctions within a building. It relies on linear thermal transmittance, which quantifies the rate of heat transfer for each degree of temperature difference along a thermal bridge, measured in W/mK.

This calculation helps to evaluate the total heat loss in a building caused by thermal bridges—areas where two thermal components meet and allow heat to flow more readily than the surrounding materials. This differs from U-Values, which focus solely on heat loss through individual thermal elements like walls, floors, and windows.

When is a PSI-Value Calculation needed?

When you request a SAP or SBEM assessment for your building without specifying unique PSI-Values, a default PSI-Value will be applied. This default is typically lower than the actual PSI-Value of your building, which could impact your compliance with standards. By calculating a specific PSI-Value during your assessment, you can achieve greater accuracy compared to relying on an assumed value, thereby enhancing the likelihood of your property meeting compliance on the first attempt.

It's important to note that the Building Regulations/Standards mandate that all SAP and SBEM assessments must include a thermal bridging component, regardless of whether you provide a separate PSI-Value. This is particularly vital if you're aiming for higher sustainability levels.