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 records, 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.

• What to have ready

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.

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.

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.

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.

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

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.

Call us on 07492 575 396, send a WhatsApp message, email contact@luminousanddeliver.co.uk, 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).

Typically 45 minutes for a studio and up to 2 hours for a 5+ bedroom property. We’ll provide an accurate time estimate when you book.

No specific preparation is required. Just provide normal access to all rooms, loft hatches if accessible, the boiler, hot water cylinder, and any heating controls. Documentation such as boiler service records or insulation guarantees can be helpful but is not required.

Standard lodgement is within 72 hours of the assessment. Our next-day service lodges your certificate within 24 hours for an additional £15.

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

Your EPC includes specific improvement recommendations tailored to your property. Common cost-effective upgrades include loft insulation, LED lighting, cavity wall insulation, modern condensing boilers with smart controls, double glazing, and renewable systems like solar PV or heat pumps.

For most London properties, the highest-return upgrades are LED lighting (low cost, immediate impact), loft insulation, a modern condensing boiler with proper controls, and cavity wall insulation where applicable. Solar PV and heat pumps deliver bigger rating jumps but require larger investment.

Your current EPC remains valid for 10 years regardless of improvements. However, if you want the new, higher rating to appear on the EPC Register (for example to prove MEES compliance or support a sale), you’ll need a fresh assessment.