EPC reference

EPC glossary: key terms explained

This is a reference page. It gathers the words you are most likely to meet on an Energy Performance Certificate and across our guides, and explains each one in plain English. Use it alongside our guide to reading an EPC when a term is unfamiliar.

Ratings, bands and scores

Energy Efficiency Rating: The headline measure on a domestic EPC, shown as a score from 1 to 100 and grouped into a letter band. It reflects the property’s modelled energy performance under standard assumptions, rather than the actual bills of one household.
Band (A to G): The letter grade that summarises the rating, from A (most efficient) to G (least). On the current domestic scale, A is 92–100, B is 81–91, C is 69–80, D is 55–68, E is 39–54, F is 21–38 and G is 1–20.
Asset rating: A rating based on the building’s fabric and fixed services – construction, heating, hot water, ventilation and lighting – assessed under standard occupancy. It describes the property itself, not the way the current occupants happen to live in it.
Potential rating: The band the model estimates the home could reach if the recommended cost-effective measures were installed. It is a scenario for comparison, not a quote, specification or guarantee of a result.
Primary energy: A measure of energy use that counts the energy consumed at source, including the losses in generating and delivering it, usually expressed per square metre of floor area per year. It appears alongside the efficiency rating on current certificates.
Environmental impact (CO2): A separate indicator of the carbon dioxide the home is modelled to produce. A property can score differently on cost efficiency and on carbon – for example where it uses a low-cost but higher-carbon fuel, or the reverse.

How the assessment is produced

SAP (Standard Assessment Procedure): The government’s methodology for calculating the energy performance of dwellings. Full SAP is used for new-build homes, typically worked out from construction drawings and specifications.
RdSAP (Reduced Data SAP): A simplified version of SAP used to assess existing homes from a site visit. The assessor records the features that can be observed and applies standard assumptions where information is not available.
Domestic Energy Assessor (DEA): The accredited professional who inspects a home and lodges its EPC. Domestic certificates must be produced by an accredited assessor using the appropriate methodology.
Recommendations: The list of suggested improvements on the certificate, generated by the model. They are generic prompts to investigate rather than a specification tailored to the building’s condition, access, permissions or budget.
Floor area: The total internal floor area used in the calculation, measured by the assessor. Because several figures on a certificate are expressed per square metre, an inaccurate floor area affects them.

Terms that are easy to mix up

Asset rating versus actual bills – the EPC models standard use, not your household.
Current rating versus potential rating – one describes today, the other an if-improved scenario.
Efficiency rating versus environmental impact – cost efficiency and carbon are separate scores.
Recommendations versus a survey – the list is a prompt to look into, not a professional assessment.

Building fabric and heat

Solid wall and cavity wall: Cavity walls have a gap between two leaves of masonry that can often be insulated; solid walls have no such gap and usually need internal or external insulation instead. The wall type strongly influences which measures suit a home, a point our guide to improving your EPC rating looks at in more detail.
U-value: A measure of how readily heat passes through part of the building, such as a wall, roof or window. A lower U-value means less heat is lost through that element.
Heat loss: The escape of warmth from a home through its fabric – walls, roof, floor and windows – and through air movement. Reducing it is usually the starting point for improving comfort and efficiency.
Ventilation: The controlled exchange of indoor and outdoor air that manages moisture and air quality. Work that makes a home more airtight needs to keep adequate ventilation so the building stays healthy and dry.
Main heating and controls: The primary system that heats the home, together with the controls – thermostats, programmers and thermostatic radiator valves – that govern it. Both the system and its controls affect the modelled rating.

Records, rules and the register

EPC register and lodgement: Lodgement is the act of the assessor filing a completed certificate onto the government-held register, where it becomes the official record. You can find an existing certificate on the official service using the address or a reference number. A domestic EPC is normally valid for ten years.
MEES (Minimum Energy Efficiency Standard): The rules that set a minimum EPC band for privately rented homes. Since 1 April 2020 a landlord in England and Wales may not let a domestic property rated below E (that is, F or G) unless a valid exemption is registered on the PRS Exemptions Register. The government has consulted on raising this minimum to band C in future; because the position and timing can change, confirm the current requirement on gov.uk. Our guide to when you need an EPC sets out when a certificate is required for letting and selling.

EPC Checker brings public EPC and property data together to help you research a home. It is a research aid, not an assessment, survey or professional, legal or financial advice. For the formal record, or to arrange a new certificate, use the official government service and an accredited assessor.