The Role of Thermal Bridging in EPC Scores – And How to Reduce It

When it comes to improving your EPC (Energy Performance Certificate) score, most people focus on obvious upgrades like insulation, double glazing, or efficient boilers. But there’s a hidden culprit that could be dragging your rating down — thermal bridging.

Understanding what thermal bridging is, how it affects your property’s energy efficiency, and most importantly, how to fix it, can make a big difference to your EPC result and your energy bills.

🔍 What Is Thermal Bridging?

Thermal bridging occurs when heat escapes through elements of a building that are more conductive than surrounding materials. These “bridges” allow warmth to bypass insulation, leading to higher heat loss and colder surfaces.

Common thermal bridges include:

• Metal wall ties in cavity walls

• Uninsulated steel or concrete beams

• Junctions between walls, floors, and roofs

• Window and door frames

• Balcony connections or external wall penetrations

Think of a thermal bridge as a shortcut for heat to escape — even if your walls are insulated, a badly designed corner or joint can become an energy-leaking weak point.

🔧 Why Does Thermal Bridging Matter for Your EPC?

Your EPC score is calculated using the SAP (Standard Assessment Procedure) or RdSAP for existing buildings. Both methodologies consider heat loss through the building fabric — and thermal bridging plays a role in this.

Here’s how it impacts your score:

• Increases heat loss through junctions

• Reduces the overall U-value performance of external elements

• Contributes to lower SAP ratings, especially in older or poorly retrofitted buildings

• May lead to condensation and mould risk, affecting the comfort and health of occupants

Result: Your property may receive a lower EPC rating due to increased heating demand, even if you’ve installed new insulation or double glazing.

📉 Where EPC Assessors Spot Thermal Bridging

EPC assessors don’t use thermal cameras or measure heat directly. Instead, they assign values based on building age, materials, and junction details. If no enhanced details are available, assessors apply a default thermal bridging factor, which can heavily penalise the SAP calculation.

Example:

• A modern extension with documented thermal bridge mitigation may score better.

• A 1970s property with unknown junction treatment may be assumed to have high thermal bridging losses — even if the insulation is decent.

🛠 How to Reduce Thermal Bridging (and Improve Your EPC Score)

Reducing thermal bridging requires a mix of smart design, good detailing, and proper material choices. Whether you’re building new or retrofitting, here’s how to tackle it:

✅ 1. Install Continuous Insulation

• Wrap the building envelope in uninterrupted insulation.

• Use external wall insulation (EWI) to eliminate cold junctions.

✅ 2. Improve Junction Detailing

• Use Accredited Construction Details (ACDs) during new builds or extensions.

• Apply thermal break strips between structural junctions (e.g., balconies and floors).

✅ 3. Use Thermal Blocks and Breaks

• Install low-conductivity blocks (e.g., aerated concrete) at thermal bridging points.

• Add insulation around steel beams and lintels.

✅ 4. Seal Gaps and Cracks

• Pay attention to air tightness.

• Use expanding foam and airtight membranes at joins and window reveals.

✅ 5. Upgrade Window and Door Frames

• Choose thermally broken frames (e.g., aluminium with a polyamide break).

• Ensure reveals are insulated and sealed.

✅ 6. Provide Evidence to the Assessor

• Document design details, U-values, and junction specifications.

• Where possible, use certified products and installation methods that can be referenced in the SAP/RdSAP calculation.

Without documented thermal bridging mitigation, assessors default to conservative estimates — which hurts your EPC score.

📈 Real-World Impact on EPC Ratings

Scenario 1:
A 1930s semi-detached house with solid walls and no thermal breaks = likely EPC rating of E or D

Scenario 2:
Same house with external wall insulation and insulated reveals = improved thermal performance, potential rating of C

🌍 Thermal Bridging and Net-Zero Goals

Thermal bridging isn’t just about EPC scores — it’s about energy waste, carbon emissions, and comfort. With the UK’s push toward net-zero buildings and stricter EPC requirements for landlords, ignoring thermal bridges will soon be a thing of the past.

🏡 Want to Improve Your EPC in London?

Book a qualified, local assessor at EPCrate.co.uk for expert advice on how thermal bridging and other details affect your EPC.
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