PSI Value Calculations

Measuring and controlling the weakest links through Thermal Bridging Analysis.

PSI Value Calculations.: It is often stated that any process, system or project is only as strong as its weakest link. In buildings, it is the junctions, where different materials are connected, that are prone to heat loss and reduce the efficiency of the property. The heat loss associated with a thermal bridge is called linear thermal transmittance or PSI value (pronounced “si”).

Two types of thermal bridges
  • A repeating thermal bridge, such as the studs in a timber or steel frame wall. The heat loss through these junctions are accounted for through conventional U-value calculations.
  • A non-repeating thermal bridges, for example a lintel above a window, the cill and jambs around openings.

The non repeating thermal bridge junctions ( PSI values) are individually measured through SAP and the heat loss through these junctions can be calculated either by adopting accredited details values or if the junctions are non standard by calculating them individually.

Calculating the actual heat loss through a thermal bridge junction can offer large savings in SAP calculations and can make the route to building regulation compliance much easier.

As a minimum designers need to be aware of and follow the Accredited Construction Details scheme. These are a standardised set of junction details that architects and builders can follow to minimise thermal bridges. The full set is available to download online at the government’s Planning Portal.

The benefits of  PSI value calculations and the related FRSI calculations can also highlight to the design team potential issues with a risk of condensation.

Abbey Consultants are able to calculate the heat loss through a thermal bridge junction using approved modelling software.

Get in touch or send an email with an outline of your Psi Value Calculations enquiry and one of the team will respond within 24 hours.

Get a Quote

Complete the form