One of the cheaper ways for a seller to break your survey is to omit an extension or loft conversion that was built without planning permission, or without building-regulations sign-off. Your conveyancer will eventually find this through standard searches, but by then you’ve already paid for the survey and quite possibly the searches themselves. It’s also the kind of issue that quietly tanks the bank’s valuation a week before exchange.
Two public registers will tell you 95% of what you need to know in five minutes, for free. This is how to use them.
Every property sale or let in England, Wales, Scotland and Northern Ireland has triggered an Energy Performance Certificate since 2008. Each certificate records the property’s total floor area. When you stack multiple certificates for the same property side by side, an extension shows up as a sudden jump in floor area between two certificates.
The official register is at find-energy-certificate.service.gov.uk. Search by postcode, click the address, and look at the inspection date. To see older certificates you have to search again with the previous owner’s certificate reference — the register doesn’t link them.
What a real extension looks like in the data:
| Inspection date | Floor area | Rating |
|---|---|---|
| 2024-05-20 | 56 m² | F |
| 2025-07-03 | 108 m² | D |
That’s a real example from CB23 7DG in Cambridgeshire. The property nearly doubled in size in 14 months, with a rating jump from F to D — almost certainly a major extension plus insulation upgrades.
Sometimes the floor area changes by 2–5 m² between certificates without any building work. Assessors measure differently — one might include the porch, another might not. A useful rule of thumb: floor-area changes greater than 8% are likely real extensions. Smaller deltas are usually just measurement noise.
Every English council runs an online planning portal where you can search for applications by address. The data is also aggregated across most councils at planit.org.uk, which is faster if you don’t know which council covers the address.
Things to look for:
Cross-reference what you saw in the EPC step. If a floor-area jump from 2018 shows up but there’s no permission, no PD declaration, and no building-regs certificate, ask the seller about it explicitly through your solicitor. They may not have known. The risk is real:
Unauthorised extensions can be subject to enforcement action up to four years after completion (ten years for change of use), and lenders can refuse to mortgage a property with outstanding compliance issues.
Planning permission is about whether you’re allowed to build. Building regulations are about whether what you built is safe. They’re separate. Many minor extensions don’t need planning permission but do need building-regs sign-off.
Local Authority Building Control records aren’t centrally published, so the council’s direct line is the only reliable route — ring them and ask for the completion certificate for the property. Many councils now offer an online enquiry form. If the certificate doesn’t exist for work you can see was done, the seller should be able to produce an indemnity insurance policy instead.
HM Land Registry publishes every recorded sale. If the property sold for £180,000 in 2017 and is now on the market for £310,000 in a flat local market, the difference often correlates with a documented extension. If the price has jumped but the data shows no extension or area change, ask why. Usually it’s a kitchen rebuild — sometimes it’s a hopeful asking price.
Public registers cover the paperwork trail. They don’t cover:
For a full picture you still need the surveyor and the conveyancer. But spending five minutes on the EPC and planning registers before instructing them can save you hundreds of pounds on a property that turns out to have unfixable paperwork problems.