You’ve insulated your walls, upgraded glazing, and replaced the boiler—yet your Energy Performance Certificate (EPC) rating still falls short. The culprit? Likely thermal bridging — a hidden pathway where heat bypasses insulation layers, quietly eroding your building’s energy efficiency.
In this article, we’ll explain what thermal bridging is, how it impacts EPC scores, why it often goes unnoticed in standard assessments, and what property owners can do to mitigate its effects.
For EPC assessments that take thermal bridging into account, visit our Services page.
1. What is Thermal Bridging?
Thermal bridges are areas of a building’s envelope where heat escapes more rapidly due to a break in the insulation continuity. Common thermal bridging points include:
Junctions between walls, floors, and roofs.
Window and door reveals.
Steel beams, balconies, and lintels penetrating insulation.
Corners where insulation detailing is poor.
While these areas may seem minor, they can account for up to 30% of total heat loss if not properly addressed.
2. How EPC Assessments Handle Thermal Bridging
In SAP (Standard Assessment Procedure) for new-builds:
Assessors input either a default thermal bridging factor (ψ-value) or use values from Accredited Construction Details (ACDs) or bespoke thermal modelling.
Default ψ-values assume poor detailing, heavily penalising EPC scores.
In RdSAP (Reduced Data SAP) for existing buildings:
Thermal bridging is handled through default assumptions based on building age and type.
If no evidence of enhanced detailing is provided, the assessor must assume worst-case bridging.
To ensure your EPC reflects actual performance, ensure your builder or energy assessor can provide documentation of construction detailing.
3. Why Thermal Bridging Can Drag Down EPC Scores
| Thermal Bridging Scenario | EPC Impact |
|---|---|
| Lack of Accredited Construction Details (ACDs) | Defaults to higher heat loss assumptions. |
| Metal structural elements bridging insulation | Major thermal loss penalty in SAP calculation. |
| Inadequate detailing around windows and doors | Increases surface heat loss, reducing EPC score. |
| Junctions at wall-floor/roof connections | Penalised in thermal performance assumptions. |
Ignoring thermal bridging can negate the benefits of high-spec insulation and glazing upgrades.
4. How to Reduce Thermal Bridging in Existing Properties
Install insulated cavity closers around window/door reveals.
Apply external wall insulation (EWI) to wrap cold junctions.
Use internal wall insulation (IWI) in targeted bridging hotspots.
Add thermal break materials (e.g., aerogel boards) in problematic junctions.
Draught-proofing alone isn’t enough; ensure continuity of insulation layers.
Book a detailed EPC assessment with EPCrate to identify thermal bridging risks via our Booking Page.
5. Thermal Imaging Surveys: Visualising Thermal Bridging
A thermal imaging survey (infrared thermography) can reveal:
Cold spots indicating thermal bridging.
Areas where insulation continuity is compromised.
Heat escaping through structural penetrations.
While not always part of a standard EPC assessment, providing a thermal imaging report can help an assessor justify improved U-values or detailing assumptions, leading to a more accurate EPC rating.
6. New-Build vs Existing Properties: Bridging Treatment Differences
| Property Type | How Thermal Bridging is Treated in EPC Assessments |
|---|---|
| New-Build Properties | SAP calculations allow for Accredited Construction Details (ACDs) or bespoke ψ-values. |
| Existing Buildings | RdSAP applies default bridging factors unless evidence of remedial detailing is presented. |
Developers should ensure their construction process includes certified detailing documentation to avoid default penalties.
7. Case Study: Thermal Bridging Rectification Boosting EPC Rating
A 1950s semi-detached property initially received an EPC Band D despite cavity wall insulation and modern double glazing. A thermal imaging survey identified significant bridging at:
Wall-floor junctions.
Around uninsulated window reveals.
Steel lintels lacking thermal breaks.
After targeted interventions (installing insulated cavity closers, applying external insulation to bridging hotspots), the follow-up EPC assessment improved to Band C.
Learn how EPCrate’s expert assessors can help document such improvements on our About Us page.
8. Documentation: Essential for EPC Assessor Recognition
To ensure thermal bridging improvements are recognised in EPC assessments:
Provide construction details or ACD certificates.
Supply thermal imaging reports showing before and after improvements.
Include product datasheets for insulation materials used at bridging points.
Conclusion
Thermal bridging is a hidden EPC killer that many property owners overlook. Even with modern insulation and efficient heating systems, untreated cold bridges can silently undermine energy performance. Through targeted interventions, thermal imaging diagnostics, and proper documentation, you can ensure thermal bridging doesn’t pull down your EPC rating.
At EPCrate, we specialise in identifying and accounting for thermal bridging improvements in our EPC assessments. Book your EPC assessment via our Booking Page or contact us through our Contact Page for expert advice on bridging mitigation strategies.
