Domestic EPC Assessments

What is an Energy Performance Certificate?

An Energy Performance Certificate (EPC) is a document that rates your property's energy efficiency on a scale from A (most efficient) to G (least efficient). It's been a legal requirement in England and Wales since 2008, and you'll need one whenever you sell, rent, or build a property.

Your EPC certificate provides two key pieces of information: your property's current energy rating, and its potential rating if recommended improvements were made. It also includes estimated energy costs and a breakdown of how your property performs across different areas like heating, insulation, and lighting.

EPCs are produced by accredited Domestic Energy Assessors following a standardised methodology called RdSAP (Reduced Data Standard Assessment Procedure). This ensures that all certificates are calculated consistently, making it possible to compare the energy efficiency of different properties on a like-for-like basis.

Your EPC certificate is valid for 10 years and is stored on a national register. Once lodged, estate agents, conveyancers, and potential buyers or tenants can access it using your property's address. For a deeper explanation of the fundamentals, see our guide to what an EPC is and why it matters.

How Are EPC Ratings Calculated?

Your EPC rating comes from a calculation called SAP (Standard Assessment Procedure), or RdSAP for existing homes. The assessor collects data about your property's construction, insulation, heating, and glazing. Software then calculates how much energy your home would need per square metre, producing a score from 1-100 that maps to bands A through G.

Band A (92-100 points) represents exceptional efficiency - typically new builds with features like solar panels, heat pumps, and very high insulation levels. Band B (81-91) is very efficient, usually modern homes with good insulation, efficient boilers, and double glazing throughout. Most new builds should achieve at least a B rating.

Band C (69-80) is considered good efficiency and is the target for most home improvement projects. Band D (55-68) is average - typical of homes built in the 1990s and 2000s. Many properties fall into this bracket, and there's usually scope for cost-effective improvements.

Band E (39-54) is below average and represents the current minimum legal standard for rental properties. Bands F (21-38) and G (1-20) indicate poor efficiency - these properties cannot legally be let without an exemption and typically have high energy bills and cold spots.

For a more detailed breakdown of what each rating means in practice, including typical energy costs, see our guide to understanding your EPC rating. We also explain how EPC ratings are calculated if you want to understand the methodology behind the numbers.

How to Improve Your EPC Rating

Every EPC lists improvements that would boost your rating. Some cost next to nothing. Others need proper investment but can jump you up two or three bands.

Loft insulation gives the best return for money. Topping up to 270mm costs £300-500 and can add several points to your rating. Most people can do it themselves. We've written about loft insulation and EPCs, plus keeping loft storage access after insulating.

Cavity wall insulation is another high-impact improvement if your property has unfilled cavities. At £500-1,500, it typically pays back within 3-5 years through energy savings. Our article on cavity wall insulation and EPCs explains what to expect.

Boiler upgrades often deliver the single biggest improvement to your rating. Replacing an old G-rated boiler with a modern A-rated condensing model can improve your EPC by 10-15 points. If you're refurbishing your home, coordinating the boiler replacement with other works makes sense.

Heating controls are low-cost improvements with good impact: adding a programmer, room thermostat, and thermostatic radiator valves (TRVs) typically costs £150-400 and can add 2-5 points to your rating.

Lighting improvements have become easier as LED bulbs have dropped in price. Replacing all traditional bulbs with LEDs costs £50-150 and contributes to your rating. See our comparison of LED vs traditional lighting.

More detail in our guide to improving your EPC score.

How Long Does an EPC Assessment Take?

A domestic EPC assessment takes 30-45 minutes for most properties. Larger homes or those with extensions may need an hour. Someone over 18 needs to be there to let the assessor in and provide access to all rooms, the loft, and the boiler.

During the visit, the assessor will measure the property's dimensions, inspect and photograph key features, and record details about the construction, heating systems, and energy efficiency measures. This includes checking wall types, measuring loft insulation depth, noting window types and glazing, inspecting the boiler, and documenting heating controls.

Having documentation ready helps ensure your property gets the best possible rating. Useful documents include boiler installation certificates, FENSA certificates for windows, building regulations certificates for extensions, and receipts for insulation work. Without evidence, assessors must make assumptions - which are often more conservative than the reality.

After the site visit, the data is entered into approved software which calculates the rating. For most properties, your EPC certificate can be lodged on the government register and emailed to you the same day.

For a detailed walkthrough, read our guide on what happens during an EPC assessment.

How Long Does an EPC Certificate Last?

An EPC certificate is valid for 10 years from the date of issue. During that time, you can use the same certificate for multiple sales or lettings - there's no requirement to get a new one each time, provided the existing certificate hasn't expired.

That said, there are times when getting a new EPC certificate makes sense even if yours hasn't expired. If you've upgraded the boiler, added insulation, or replaced the windows, your old certificate won't show these improvements. A fresh one could bump you up a band or two, which helps when selling or letting.

For landlords, a better rating might mean the difference between meeting MEES requirements and needing to make further improvements. For sellers, properties with higher EPC ratings can be more attractive to buyers and may benefit from green mortgage products offering preferential rates.

For more on this topic, see our article on what happens when an EPC expires.