It’s one of the most confusing things for homeowners and landlords: two houses that look the same, were built at the same time, and sit next door to each other — yet they receive very different EPC ratings.

This isn’t a mistake. It’s a result of how EPCs are calculated, what assessors can and cannot assume, and how property data is recorded.

Let’s break down exactly why this happens, what causes it, and what you can do about it.

1. EPCs Are Based on Recorded Evidence — Not Assumptions

Even if two homes were built identically, EPC assessors are not allowed to assume they still are.

If one owner can prove upgrades and the other cannot, the EPCs will differ.

For example, one homeowner may have documentation for insulation or heating upgrades while the other does not — and only the documented upgrades can be included by the assessor. This is why working with an experienced assessor matters — see our EPC Assessors in London page to learn how professional assessments ensure accuracy.

2. Small Data Differences Can Shift the Rating Band

EPC bands are based on SAP scores, and even a 1–2 point difference can move a property into another band.

This is why minor variations — such as slightly different insulation depth or a marginally newer boiler — can result in different EPC ratings.

If you suspect your rating doesn’t reflect your property fairly, you can book a reassessment to ensure all features are properly recorded.

3. Heating System Efficiency Matters More Than Appearance

Two identical homes with different boiler ages or heating systems will score differently.

Upgrading to a modern boiler or adding smart heating controls can noticeably improve your rating — and checking upgrade costs in advance via transparent EPC pricing helps avoid surprises.

4. Documentation Changes Everything

Assessors can only include what they can verify. If insulation, renewables, or efficiency upgrades are hidden and undocumented, they are excluded.

If you’re unsure what qualifies or how assessments work, you can read more about EPCrate on the About Us – EPC Company London page.

5. Extensions and Layout Changes Add Up

Even small changes like conservatories or loft conversions affect heat-loss calculations and therefore EPC scores.

Professional assessors account for this accurately, which is why using accredited specialists — like those on our EPC Assessors London team — is essential.

6. Assessors Are Human — Data Entry Matters

While EPC standards are strict, small data-entry differences can affect outcomes. Experienced assessors reduce this risk and can explain your results clearly.

If you have questions about your certificate, the best place to start is our Contact Us – EPC Services London page.

7. Timing and Methodology Matter

EPC rules and modelling assumptions evolve. A property assessed years ago may score differently today under updated standards.

This is another reason to review older certificates and consider updating them when selling or renting.

Final Thoughts

Two homes can look identical — but EPCs are built on verified data, not appearance.

Small differences in documentation, heating systems, insulation, or recorded measurements can create noticeable differences in ratings.

Understanding this protects you from confusion, disputes, and bad decisions — and ensures your property is represented accurately and fairly.

If you want to check or update your EPC, book an assessment or contact our team through the EPCrate Contact Page.

You can contact EPCrate to review or challenge your EPC if you suspect errors: Contact Us – EPC Services London.

📍 Address: 150–160 City Road, London, EC1V 2NX
📞 Phone: 020 3488 4142
📧 Email: info@epcrate.co.uk