What Does an EPC Assessment Include? What Assessors Check and How Ratings Are Calculated

An Energy Performance Certificate (EPC) assessment follows a standard methodology, but the outcome can vary significantly depending on how a property is constructed, heated and insulated.

Understanding what an assessor looks at helps property owners prepare properly and avoid some of the most common EPC issues.

What Happens During an EPC Assessment?

An EPC assessment is a non-intrusive inspection carried out by a qualified Domestic Energy Assessor. The visit typically lasts between 45 and 60 minutes, depending on the size and complexity of the property.

The assessor records physical characteristics of the building, which are then entered into approved EPC software to calculate the final rating.

Heating Systems and Controls

One of the most influential factors in an EPC is the heating system. The assessor will record:

• Boiler type and fuel
• Age and efficiency of the system
• Heating controls such as programmers, thermostats and TRVs

Missing or undocumented controls can result in a lower rating, even where a modern boiler is installed.

Insulation Levels

Insulation has a major impact on EPC scores. During the assessment, the assessor will check:

• Loft insulation depth (where accessible)
• Wall construction (solid, cavity, or filled cavity)
• Roof and floor construction

In older housing stock, insulation is often assumed to be absent unless it can be clearly evidenced.

Windows, Glazing and Doors

The assessor will note the type of glazing installed throughout the property, including:

• Single, double or triple glazing
• Frame material
• Extent of glazing

Documentation such as FENSA certificates can help confirm installation dates where relevant.

Lighting and Fixed Low-Energy Fittings

EPCs consider the proportion of fixed low-energy lighting in the property. Portable lamps are not included.

This is one of the simplest areas where ratings can be improved with minimal cost.

Extensions and Alterations

If a property has been extended or altered, the assessor must record:

• Construction type of extensions
• Build age
• Heating arrangements

Inconsistent construction across extensions is a common reason EPCs score lower than expected.

Why Small Details Matter

EPC ratings are calculated using standardised assumptions. Where evidence is missing or access is restricted, the assessor must apply conservative defaults.

This is why preparation matters — and why many EPC-related delays are avoidable, as explained in our guide on common EPC mistakes that delay property sales and rentals.

How EPC Assessments Affect Sales and Rentals

EPC results increasingly influence buyer and tenant behaviour, as well as lender discussions. The wider impact of EPC ratings on the property market is explored in our article on how EPC ratings affect house prices, rentals and buyer demand.

Assessment outcomes can also affect how quickly properties are marketed in busy areas such as Stoke-on-Trent or Chelmsford, where compliance checks are often time-sensitive.

How Much Does an EPC Assessment Cost?

EPC pricing varies depending on property size and layout. A full breakdown of typical costs is covered in our guide on how much an EPC costs in the UK.

Booking an EPC Assessment

If you need a new EPC or are preparing a property for sale or letting, arranging an assessment early helps prevent delays.

EPC assessments can be booked online via the booking page.

Conclusion

An EPC assessment follows a consistent process, but the final rating depends on the details recorded during the visit. Understanding what assessors check allows property owners to prepare properly and ensure the certificate accurately reflects the building.