Thermal Bridging Calculations
Thermal bridging, or psi-value calculations, assesses heat loss at junctions in a building’s fabric. These weak points, such as wall-floor connections or window openings, can account for 20–30% of total heat loss. Using accurate psi-value calculations rather than default values helps ensure compliance and avoid unnecessary energy waste.
What Is a Psi Value?
A Ψ‑value (psi value) measures linear heat loss along a junction between two thermal elements, such as where an external wall meets the floor or roof. The value is expressed in W/m·K and indicates heat loss per metre at that junction. These values are used in energy assessments such as SAP or SBEM to model non-repeating thermal bridges accurately.
Why Accurate Thermal Bridging Matters
Using default psi values assumes worst-case heat loss, which can make it difficult or impossible to comply with efficiency standards under updated regulations. Bespoke calculations often show better performance than defaults, improving energy efficiency, reducing heating costs, and raising SAP and EPC ratings.
A thermographic survey can help identify actual thermal bridges and insulation gaps, providing accurate data to support these calculations.
Typical Junctions Assessed
Common thermal-bridge junctions include:
External wall to ground floor connections
Wall to roof joints and eaves
Window and door openings (sills, jambs, lintels)
Balconies or cantilevered features intersecting insulation layers
Intermediate floor junctions in multi-storey buildings
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Designing Junctions to Minimise Heat Loss
Through the use of psi-value calculations, building junctions can be carefully designed and properly insulated. This significantly reduces heat escaping through thermal bridges, minimising energy waste and lowering fuel bills. Optimised junctions not only improve building performance but also help achieve regulatory compliance and enhance overall occupant comfort.
How We Work
Our technical team uses specialist thermal-modelling software to calculate psi values. We analyse your construction details and provide a clear report summarising junction performance, heat loss, and any recommended improvements. Calculations are tailored to your project, from single dwellings to multi-unit developments, ensuring accurate SAP or SBEM compliance.
Long-Term Benefits of Bespoke Psi Calculations
Bespoke psi values can be reused on future projects with the same build-up, streamlining compliance for repeated designs. They often reduce the need for excessive insulation or additional measures, helping manage build costs while achieving regulatory requirements.
Reduce Heat Loss with Expert Thermal Bridging Analysis
Ensure your junctions are well designed and insulated. Melin Energy Consultants provide precise psi-value calculations to minimise thermal bridging, cut energy waste, and achieve SAP and SBEM compliance.