Why Is My EPC Rating Different From My Neighbour's?

If you have ever compared your EPC with a neighbour's and wondered how two houses on the same street ended up in different bands, you are asking a reasonable question. It comes up on almost every job.

The short answer is that an EPC describes one specific property, assessed on one specific day, under one specific methodology. Change any of those and the result can legitimately change with it.

Two houses, one street, different ratings

Start with the thing most people never think about: where the house sits in the row.

A mid-terrace home has two exposed external walls. The neighbouring properties on either side are heated too, so very little heat escapes sideways. An end-terrace has three exposed walls. A semi-detached house also has three. A detached house has four.

That difference exists before you consider insulation, glazing or heating. Two houses built by the same builder in the same year, with identical windows and identical boilers, will not produce identical results if one is mid-terrace and the other is on the end.

After that, the usual suspects:

• Floor area, extensions and layout. A rear extension changes the heated envelope and often the wall-to-floor ratio.
• Wall, roof and floor construction. Solid brick behaves very differently from a filled cavity.
• Loft insulation depth — and whether it can actually be inspected on the day.
• Windows and glazing. Age and specification both matter, not just "double glazed".
• Boiler, heating controls and hot-water cylinder, including cylinder insulation type and thickness.
• Heat pumps, solar PV or other renewables.
• Lighting — the proportion of fixed low-energy fittings.
• When work was done. Two lofts converted a decade apart were built to different standards.

Any one of these can move a property within a band. Several together can move it across one.

Improvements that cannot be seen

This is the reason that surprises people most.

An EPC records what the assessor can verify — either by seeing it, or through supporting evidence they can accept. Some improvements are genuinely invisible once finished. Underfloor insulation beneath a fitted carpet. Cavity fill in a wall that looks exactly like an unfilled one. Insulation behind a plasterboard dry lining.

When something cannot be confirmed, the methodology may require a default assumption based on the age and type of the property. That default can be less favourable than what is actually installed.

So two identical houses can diverge simply because one owner kept the installer's paperwork and the other did not. It is not that the assessor disbelieved anyone — an assessor cannot record an improvement on the strength of being told it is there.

That is why we ask about documents before the visit. Certificates, invoices, building-control paperwork and commissioning documents can all help, where they exist and where they can be accepted as evidence. Our preparation and evidence guide covers what is worth digging out, and what to have ready sets out the access side.

To be precise about what evidence does: it changes what can legitimately be recorded, not what the rating will be. Paperwork does not guarantee a better result. It just means a genuine improvement is less likely to go uncredited.

Old EPC versus new EPC

If you are comparing your new certificate against one from a few years ago, there is a further factor.

Since 15 June 2025, existing dwellings in England and Wales have been assessed under the RdSAP 10 methodology, replacing the approach used for older EPCs. RdSAP 10 remains the approved methodology under the government's current notice of approval.

RdSAP is a reduced-data version of the full SAP calculation, used for existing homes because the complete construction data a new-build assessment relies on is rarely available for a property already standing. The methodology has been updated to reflect newer building technologies, heating systems, renewable technologies and more detailed property information.

So older and newer EPCs may differ because the methodology, the data requirements, the property evidence and the technologies considered have all evolved. Energy-efficiency technology and assessment methods have moved on, so today's EPC looks at some parts of a property differently, and in more detail, than an older assessment did. That is a change in how a home is assessed and recorded — not a judgement that older homes or older building standards are now "bad", and not a requirement to modernise anything.

Because of that, a new EPC should not be expected to reproduce an older certificate exactly, even if the property itself has not changed very much. An older EPC reflects the methodology and information available at the time; a current EPC assesses the property using today's approved methodology.

Two things are worth being careful about:

1. This does not mean an older EPC was wrong. It was produced under the rules that applied then.
2. There is no published rule that RdSAP 10 raises or lowers ratings. The result depends on the individual property, the features present, the evidence available and the methodology used. Anyone telling you the update always moves ratings one way is overstating it.

Our deeper write-up of the change is in RdSAP 10: what changed in 2025.

Comparing EPCs? Compare the property details and the assessment methodology — not just the letter rating.

Who actually decides the rating

Worth stating plainly, because it is the question we are asked most.

The assessor's job is to survey the property, record its physical characteristics and systems accurately, and verify what evidence can be accepted. That data then goes into government-approved software, which calculates the rating.

There is no field an assessor can edit to produce a requested result. If there were, the certificate would be worthless to the buyer, tenant or lender relying on it — and the assessor would be risking their accreditation over it.

What an assessor can do is make sure everything genuinely present is recorded and properly evidenced. That is the entire value of preparing well for the visit.

If you think a certificate is wrong

Differences between two EPCs are normal and are usually explained by the factors above. But certificates can contain incorrect information, and it is fair to check.

Start with the property details recorded on the certificate, not the rating. The rating follows from the data, so if the data is wrong the rating will be too. Look at the recorded floor area, wall construction, roof insulation, glazing and heating system, and see whether they match the property you know.

If something is genuinely wrong, raise it with the assessor who produced that certificate first. Every accredited assessor belongs to a scheme with a formal complaints process. A difference between two certificates is not, by itself, evidence that either is mistaken.

Getting a certificate that reflects your home

Most of what makes a fair, accurate EPC is decided before the assessor arrives: access to every room, the loft and the meters, and any paperwork for improvements that cannot be seen.

We cover all 32 London boroughs from our base in Stratford, with guide prices based on internal floor area and your exact quote confirmed before booking. See what a domestic EPC includes, the full guide pricing, or send us the address and we will come back with a price.