An older EPC may still be valid after an extension, but it may no longer describe the home you plan to sell or let. Here is how to decide what to do. This guide is written for practical decision-making and links to the sources used for verification.
The certificate does not update with the building work
You have finished a rear extension and the EPC on the register still shows the original house. Does the work automatically cancel it? For an existing dwelling, government guidance says an EPC normally remains valid for ten years, unless a newer certificate is lodged for the same building. A routine extension is not described as an automatic expiry event. Check the date and the exact property covered before assuming you need another assessment.
Validity is only half the question. A buyer or tenant looking at an older EPC may reasonably think its floor area, glazing and heating description reflects today's home. If those features changed materially, the certificate can remain legally valid while offering a poor picture of the property now being marketed.
What might change in the rating?
An assessor visiting today would record the home as it stands, including the extension's size, construction, windows and fixed heating. A loft conversion, new roof insulation or an altered heating system can also change the inputs. Do not assume the new EPC will be better: extra glazing or floor area may affect the calculation as well as improved insulation.
An EPC uses a standard method rather than your household's actual energy bills. That is why a builder's promise of a particular band is not the same as a lodged certificate. If the project created a genuinely separate flat or dwelling, the certificate boundary needs its own assessment rather than a simple update to the old house record.
Give the assessor the evidence, not a target grade
Keep the completion and compliance paperwork from the works. GOV.UK advises homeowners to retain Building Regulations certificates because they may be requested on sale. Plans, insulation specifications and installer documents can also help an assessor identify construction that is hidden behind finished surfaces. The assessor must still inspect the property and apply the approved EPC method; paperwork does not guarantee a particular result.
Check the existing certificate on the official register before paying for another one. If it has expired, is missing or covers the wrong unit, resolve that before marketing. If it is valid but predates substantial work, a fresh assessment may be worthwhile so the listing describes the home buyers or tenants will actually see.
- Check the EPC address, date and floor area
- Gather extension plans and Building Regulations records
- Tell the assessor about hidden insulation and heating changes
- Ask separately about a newly created self-contained dwelling
Book for the home that exists now
CertifyEPC can arrange a domestic EPC assessment across London. Tell us whether the property has an extension, loft conversion or other recent work when requesting a quote; that helps establish the right scope and access. The accredited assessor determines the rating after the visit, and the new lodged certificate supersedes the earlier one.
Research and verification
Authoritative sources
Use these primary and specialist sources to check the current rule and read further.
Requirements can change and unusual properties may need specialist advice. Check the latest official source and the facts of the property before relying on a compliance conclusion.
