Is Draught-Proofing Overrated? What the EPC Doesn’t Reflect Accurately?

You seal the gaps, fit door brushes, insulate around windows, and block floorboard leaks—yet your EPC score barely improves. So, is draught-proofing overrated, or is the problem with how EPCs assess energy efficiency?

The truth is more nuanced: draught-proofing is a highly effective real-world upgrade, but the EPC system often fails to reflect its full value. Here’s why.

1. What EPCs Actually Measure

EPCs (Energy Performance Certificates) are based on SAP (Standard Assessment Procedure) or RdSAP for existing homes. The system calculates theoretical energy performance, using assumptions about:

• Wall, roof, and floor insulation

• Glazing and doors

• Heating and hot water systems

• Lighting

• Air permeability (draughts/air leakage)

But here’s the catch: unless there’s formal evidence (like an air pressure test), the EPC assessor must use default assumptions for air tightness.

👉 Result: All your manual draught-proofing efforts may not be factored in at all.

2. Why Draught-Proofing Is Still Valuable

Just because it doesn’t show up on the EPC doesn’t mean it’s pointless:

• Reduces uncontrolled heat loss

• Improves thermal comfort

• Lowers heating demand and bills

• Prevents cold spots and condensation issues

• Reduces reliance on central heating

In short, draught-proofing can dramatically improve your living experience and energy use—even if the EPC rating barely changes.

3. The EPC Software’s Blind Spot

Without a formal air tightness (blower door) test, EPC software assumes air leakage rates based on:

• Property age

• Construction type

• Window and door condition

So unless your draught-proofing is:

• Professionally certified, or

• Part of a broader retrofit with documented evidence,

…it’s invisible to the EPC.

👉 Even highly sealed homes will be rated like leaky ones if not tested.

4. Common Draught-Proofing Measures the EPC Ignores

• Self-installed letterbox covers and keyhole brushes

• Sealed skirting board gaps

• Window film kits and door seals

• Floorboard filler and under-door draught stoppers

• Chimney balloons or flue blockers

These upgrades may save you significant heating energy—but unless your EPC assessor sees formal air permeability proof, they don’t help your score.

5. How to Get Credit for Draught-Proofing in Your EPC

✅ Book an air pressure test: It’s the only way to prove airtightness and override default assumptions.

✅ Include draught-proofing in a professional retrofit package: Combined with other upgrades, it becomes part of a documented improvement.

✅ Photograph and list your draught-proofing for the assessor—while not guaranteed, some assessors may use slightly adjusted values if they can see effort has been made.

Final Verdict: Draught-Proofing Isn’t Overrated—Just Undervalued

Draught-proofing is one of the most cost-effective and comfort-enhancing upgrades you can make to a home. But under the current EPC framework, it’s systematically undervalued—unless verified through specific tests.

If your goal is real-world efficiency: draught-proof away.
If your goal is an improved EPC rating: combine it with documented upgrades and consider an air test to truly reflect your home’s airtightness.

Want an accurate EPC that reflects your upgrades?
Book a detailed EPC assessment with an experienced assessor who understands how to capture draught-proofing the right way.