EPC questions, answered

No. The assessor surveys the property, records its measurements, construction, heating, glazing and lighting, and verifies any evidence they can accept. The rating is then calculated from that data by government-approved software. There is no field an assessor can edit to reach a requested result, and doing so would put their accreditation at risk. What an assessor can do is make sure everything genuinely present is recorded and evidenced.

• Why EPC ratings differ between similar homes

EPC ratings are specific to the individual property. Position in the terrace is a common reason: a mid-terrace home has two exposed external walls where an end-terrace or semi has three, which changes heat loss before anything else is considered. Floor area, extensions, insulation, glazing, heating, renewables and the evidence available on the day all vary between neighbouring homes too.

• Why EPC ratings differ between similar homes

Existing dwellings in England and Wales have been assessed under the RdSAP 10 methodology since 15 June 2025, the first substantial change to the calculation in over a decade. A new certificate will not necessarily reproduce an older one even where the property is unchanged. There is no published rule that the update moves ratings up or down. It depends on the property. Previous certificates can also record different assumptions or information.

• RdSAP 10: what changed in 2025

RdSAP is the methodology used to calculate EPCs for existing homes. RdSAP 10 became the approved methodology for existing dwellings in England and Wales on 15 June 2025. It collects more detail about the property and calculates a number of things differently from the version it replaced.

• RdSAP 10: what changed in 2025

None are compulsory, but where they exist they can help: window and door installation certificates, loft, wall or floor insulation certificates or guarantees (with their certificate or guarantee number), building-control paperwork for extensions, boiler and hot-water cylinder details, heat-pump commissioning documents, and solar or MCS documentation. They matter because an improvement that cannot be seen or evidenced may have to be recorded using a default assumption instead.

• Documents and evidence that may help

Where an improvement cannot be inspected and there is no evidence the assessor can accept, the methodology may require a default assumption based on the age and type of property, which can be less favourable than what is actually installed. Supporting paperwork changes what can legitimately be recorded. It does not guarantee a particular rating.

• Documents and evidence that may help

They are useful where you have them, but they are not mandatory. MCS paperwork, commissioning documents or system specifications are examples of evidence an assessor may be able to accept to confirm what is installed, rather than estimating it. The assessor decides what can be accepted under the methodology.

• Documents and evidence that may help

Our quote is based on the property information supplied before the appointment. If the property is materially larger or more complex than described (a significant undisclosed extension, an unmentioned loft conversion, or an unusually complex layout), we explain any adjustment and confirm it with you before the assessment begins, never afterwards. In practice this is rare.

• See guide pricing

An Energy Performance Certificate (EPC) is an official UK government document that rates a property’s energy efficiency from A (most efficient) to G (least efficient). It shows current and potential energy efficiency, estimated annual energy costs, CO₂ emissions, and recommendations for improvement.

• EPC ratings explained
• Domestic EPC service

An EPC is valid for 10 years from the date of issue. After 10 years, you’ll need a new EPC if you’re selling or letting the property.

• How long an EPC lasts

Your EPC shows the current rating (A–G), the potential rating after recommended improvements, estimated annual energy costs, CO₂ emissions, and a list of specific improvement recommendations with estimated costs and savings.

• EPC ratings explained

Only an accredited Domestic Energy Assessor (DEA) registered with a government-approved scheme can issue a domestic EPC. We are accredited with two government-approved schemes, Elmhurst Energy and Quidos. Every EPC we produce is lodged on the official UK Government EPC Register.

• Your accredited assessor
• Domestic energy assessor in London

The rating is calculated using the Reduced data Standard Assessment Procedure (RdSAP), currently RdSAP 10. The assessor records construction details, insulation, heating, hot water, lighting, windows, and ventilation. The software calculates a Standard Assessment Procedure (SAP) score from 1–100, which maps to a band from A to G.

• How your EPC rating is calculated
• RdSAP 10: what changed in 2025

Call us on 07492 575 396, send a WhatsApp message, email [email protected], or use our online booking form. Phone, WhatsApp and email all reach the assessor directly, and we reply during our opening hours (Monday–Sunday, 8am–8pm).

• Get your exact quote

Typically 45 minutes for a studio and up to 90 minutes for a 5+ bedroom property. We’ll provide an accurate time estimate when you book.

• What happens during an EPC assessment

Mostly access. Every room, the loft hatch (if there is one), the boiler, hot water cylinder, heating controls and meters need to be reachable, and someone needs to be there to let the assessor in. Paperwork is not compulsory, but hidden insulation can only be recorded from documents: have the insulation certificate or guarantee ready, with its certificate or guarantee number. Without evidence, the method uses the default for the age of the home. A heating system that is fitted but cannot be inspected, with no paperwork for it, means the EPC cannot be finished until access is given.

• What to prepare
• What to have ready

Standard lodgement is within 72 hours of the assessment. Same-day lodgement puts your certificate on the register on the day of the visit for an additional £15.

• The Domestic EPC process

Yes. We’re happy to share our Elmhurst Energy and Quidos accreditation details on request. You can also verify any Domestic Energy Assessor on the EPC Register at gov.uk.

• Assessor credentials

Older EPCs were done under earlier versions of the method, some well over a decade ago. Standards and assumptions have moved on since, so some things that used to score well don’t carry the same weight now. Since June 2025, existing homes are assessed under RdSAP 10, which is more detailed. A new EPC isn’t a like-for-like comparison with an old one, even if the home hasn’t changed.

• The method changed in June 2025

Their EPCs may have been done before June 2025 under the older method, or may have expired. Homes that look alike can also differ in floor area, how many outside walls they have (an end or mid terrace), insulation, heating, and the paperwork that was available on the day. Compare the property details on each certificate, not just the letter.

• Why your EPC may differ

An EPC counts specific things: insulation, windows and doors, heating and hot water, heating controls, lighting and renewables such as solar panels. Changes like dividing a room with partitions or curtains, decorating or new flooring don’t count. Some upgrades count for less than people expect, and going from C to B usually needs solar panels.

• What counts towards your rating

Insulation can only be recorded if your assessor can see and measure it, or if you have paperwork that shows it’s for your home and states the thickness. If the loft couldn’t be reached, or the insulation was covered, the method has to use a default instead. Send us the paperwork with the thickness before your EPC is lodged and we’ll check whether it can be recorded.

• Documents that may help

Insulation inside a wall can’t be seen, so it’s recorded from evidence that clearly relates to your home, to those walls, and to the work being done, and that shows how thick the insulation is. Documents about other work, such as the loft or the windows, can’t be used for the walls, and a photo with no measurement can’t show the thickness. An extension is recorded separately from the main building, so it needs its own evidence too. What helps: a Building Control completion certificate, the installer’s guarantee or specification stating the thickness, or photos taken during the work showing the insulation with a tape measure against it. Your assessor has to be able to rely on it, so we’ll tell you if something can’t be used.

• Documents that may help

Where a loft is insulated at both the joists (the loft floor) and the rafters (the roof slope), the method counts the joist insulation only. We can photograph and note what we see, but the rafter insulation won’t change the rating.

No. The rating is worked out by approved software from what was recorded and evidenced, and we can’t move it, even by a point. That stays true if the home isn’t being sold or let, or the EPC is for your own records. If you have paperwork for something we couldn’t see, send it before the EPC is lodged and we’ll check whether it can be recorded.

• How your EPC rating is calculated

Yes, it’s a strong result for an existing home. The current legal minimum for letting a home is E. The government has confirmed a C target for rented homes from 1 October 2030, but that still needs legislation.