Thermal Bridging Calculations UK | 2D ψ-Value

Q: What is a thermal bridge and why does it cause problems in retrofit?

A thermal bridge is a point or linear area in a building's fabric where heat loss is significantly higher than through the surrounding construction, typically at junctions such as wall-to-floor, wall-to-roof, window reveals, and structural elements. Thermal bridges cause localised cold spots, increase energy loss, and can lead to surface condensation and mould growth. In retrofit, poorly managed thermal bridges can undermine the performance gains from insulation.

Q: What is a ψ-value (psi-value) calculation?

A psi-value is a linear thermal transmittance value that quantifies the additional heat loss per metre length of a junction in W per metre Kelvin. It is calculated using two-dimensional finite element thermal modelling software and is required to accurately account for thermal bridging in SAP calculations. Using calculated psi-values instead of default Appendix K values in SAP can significantly improve a property's energy rating.

Q: What software and standards does StepSoft use for thermal bridging analysis?

StepSoft thermal bridging calculations are carried out using approved two-dimensional finite element analysis software in accordance with BS EN ISO 10211. The team is also an Elmhurst Approved PSI Value Competency Scheme Member, confirming that calculations meet the quality standards required for use in SAP assessments and scheme submissions.

Q: Can thermal bridging calculations improve a property's EPC rating?

Yes. Using calculated project-specific psi-values rather than default Appendix K values in SAP modelling can improve a property's calculated energy performance and EPC rating, because default values are deliberately conservative. This can be particularly valuable for properties where achieving a specific EPC band is required for funding eligibility under ECO4 or other schemes.

Thermal Bridging Calculations

At StepSoft Coordination Services, we provide accurate thermal bridging calculations to identify heat loss at critical junctions within building structures. Our expert analysis helps improve building energy performance and ensures compliance with PAS 2035 and building regulations. By addressing thermal bridges effectively, we support energy-efficient and sustainable retrofit solutions.

What are Thermal Bridging Calculations?

Thermal bridging calculations analyze areas in a building where heat flow is higher due to structural junctions, such as where walls meet floors, roofs, or windows. These areas, known as thermal bridges, can lead to increased heat loss, reduced energy efficiency, and potential moisture problems.

Reduce Heat Loss

Identifies areas where heat escapes through structural junctions.

Improve Energy Efficiency

Supports better insulation performance and overall building efficiency.

Prevent Moisture & Condensation

Helps reduce the risk of condensation and damp issues caused by cold surfaces.

Regulatory Compliance

Ensures compliance with PAS 2035 standards and building regulations.

Our Thermal Bridging Calculation Process

Junction Identification

Structural Analysis

2D Thermal Modelling

Performance Assessment

Reporting & Recommendations

Why Choose StepSoft Coordination Services

Benefits of Professional Thermal Bridging Calculations

Improved Energy Performance

Reduce heat loss and improve overall building efficiency.

Condensation Risk Reduction

Minimize cold spots that cause condensation and mold growth.

Optimized Retrofit Design

Provide essential data for effective insulation and retrofit strategies.

Let's Discuss Your Retrofit Needs

Accreditations & Certifications

FAQ 's

What is a thermal bridge and why does it cause problems in retrofit?

A thermal bridge is a point or linear area in a building’s fabric where heat loss is significantly higher than through the surrounding construction — typically at junctions such as wall-to-floor, wall-to-roof, window reveals, and structural elements. Thermal bridges cause localised cold spots, increase energy loss, and can lead to surface condensation and mould growth. In retrofit, poorly managed thermal bridges can undermine the performance gains from insulation

What is a ψ-value (psi-value) calculation?

A ψ-value (psi-value) is a linear thermal transmittance value that quantifies the additional heat loss per metre length of a junction in W/mK. It is calculated using 2D finite element thermal modelling software and is required to accurately account for thermal bridging in SAP calculations. Using calculated psi-values instead of default Appendix K values in SAP can significantly improve a property’s energy rating.

When are thermal bridging calculations required for retrofit projects?

Thermal bridging calculations are particularly important when installing external wall insulation (EWI), solid wall insulation, or room-in-roof insulation, where junctions between insulated and uninsulated elements must be carefully detailed. They are also required for SAP calculations supporting building regulations compliance, and are increasingly requested by scheme administrators and TrustMark auditors as part of robust PAS 2035 compliance evidence.

What software and standards does StepSoft use for thermal bridging analysis?

StepSoft’s thermal bridging calculations are carried out using approved 2D finite element analysis software in accordance with BS EN ISO 10211. The team is also an Elmhurst Approved PSI Value Competency Scheme Member, confirming that calculations meet the quality standards required for use in SAP assessments and scheme submissions.

Can thermal bridging calculations improve a property's EPC rating?

Yes. Using calculated (project-specific) psi-values rather than default Appendix K values in SAP modelling can improve a property’s calculated energy performance and EPC rating, because default values are deliberately conservative. This can be particularly valuable for properties where achieving a specific EPC band is required for funding eligibility under ECO4 or other schemes.

Does StepSoft also assess the fRSI surface temperature factor?

Yes. Alongside psi-value calculations, StepSoft assesses the fRSI (temperature factor) at junction details. The fRSI value indicates the risk of surface condensation and mould growth at thermal bridges. Under PAS 2035 and building regulations, junction details should achieve a minimum fRSI of 0.75 to prevent mould risk. StepSoft’s reports confirm whether junction details meet this standard.

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