Measured Thermal Bridging
A PSI-value (Ψ-value) is a measure of the rate of heat loss through a thermal bridge, which occurs where building elements—such as walls, floors, and roofs—intersect. Thermal bridging is also sometime referred to as cold bridges.
It is expressed in watts per metre-kelvin (W/m·K) and quantifies the additional heat loss at junctions compared to the surrounding building fabric.
Why It Matters in Building Compliance
In the context of SAP (Standard Assessment Procedure) calculations and Part L of the Building Regulations, PSI-values are critical for accurately assessing a building’s energy performance. Poorly designed or constructed junctions can significantly increase heat loss, undermining insulation efforts and increasing energy bills.
Common Thermal Bridging Junctions
Common junctions within our modelling software have corresponding E references – listed below:
- E1/2 – Lintels
- E3 – Sills
- E4 – Jambs
- E5 – Ground Floor Perimeter
- E10/11 – Eaves
- E12/13 – Gables
- E16/17 – External Wall Corners
- E18 – Party Walls
How PSI- Values Are Used
- Default values from accredited construction details can be used, but they are often conservative.
- Calculated PSI-values (via thermal modelling) can be used to demonstrate improved performance and reduce the building’s overall heat loss.
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Using accurate PSI-values in your energy calculations can help demonstrate compliance with Part L, improve your SAP score, and reduce the need for costly remedial work. For best results, consult with a qualified energy assessor or thermal modeller early in the design process.
If you have any questions or need assistance with PSI-values, don’t hesitate to contact us at Building Compliance Testing Limited.