Residential - ERS - Residential & Commercial Energy Assessments & Building Compliance
Thermal Bridging Calculations
Thermal bridging calculations, often referred to as PSI value calculations, are crucial for assessing heat loss at building junctions. These junctions are critical points that can compromise a building’s energy efficiency due to their susceptibility to heat loss.
Thermal bridging happens at specific points where building materials meet, such as corners, where walls and floors join, and around windows. These are known as non-repeating thermal bridges and are the primary focus when calculating PSI values. There are also repeating thermal bridges, which occur in patterns throughout the structure, like timber studs in walls or roof assemblies. These are addressed within the U-Value calculation of the building elements.
Accurately modelling thermal bridging can significantly impact the cost-efficiency of a build. For commercial buildings, SBEM assessments offer a choice between using a default figure or performing a detailed thermal bridging calculation. Relying on the default can lead to penalties and affect the accuracy of the SBEM results, often necessitating additional insulation to meet standards.
In domestic projects using SAP, under the previous regulations you could use ‘Accredited Construction Details’ instead of defaults or custom calculations. However, such options have been removed in SAP10, making detailed thermal bridging calculations an integral
requirement of the design process.
Your thermal bridge calculation certificate will include the following elements:
- Modelled junction and architectural detail used in the calculation.
- PSI (ψ) Value which indicates the heat loss from junctions, used in energy efficiency calculations.
- Temperature Factor (ƒRsi) which assesses the risk of surface condensation, which should be greater than 0.75.
Figures are calculated in accordance with the requirements of the following documents: EN ISO 10211 2017, EN ISO 13370 2017, EN ISO 6946 2017, BR497 (Second Edition), BR 443 2019, BRE IP1/06.
To assist with the calculations, please call us on 01865 378885, or via the Contact Us form, and we’ll be more than happy to talk you through the best approach for your EPC requirements.
