Major EPC overhaul due to take effect on 15 June 2025

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The Energy Performance Certificate (EPC) system will see the introduction of RdSAP 10 – an update to the methodology that underpins domestic energy assessments in existing homes.

 

The changes are the most significant in over a decade and are expected to improve the accuracy of EPCs, better reflect how homes are used, and help inform decisions on energy efficiency. Nevertheless, some Propertymark members have already reported increased costs for the more detailed assessments.

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What is RdSAP?

The Reduced Data Standard Assessment Procedure (RdSAP) is the simplified methodology used for producing EPCs in existing dwellings. It uses assumptions about how buildings are constructed and occupied to generate a rating of a property's energy efficiency.

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The version set to be introduced in June 2025, RdSAP 10, incorporates new data inputs, revised assumptions, and structural changes designed to bring EPCs closer to reality.

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Key changes in energy assessments

Expanded data collection

Energy assessors will now collect and record more specific information about a property, including types of glazing and their condition, heating system efficiency based on evidence such as model numbers or manufacturer data, and the presence of smart heating controls.  Home improvements, such as added insulation or new windows, will only be reflected if evidence is available.

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This means EPCs will now depend much more heavily on the documentation that homeowners, landlords, and agents can provide.

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More accurate assessment of heating systems

Previously, if a heating system’s details couldn’t be verified, default assumptions were used, often underestimating its efficiency. RdSAP 10 introduces a hierarchy that prioritises actual evidence over assumptions. If no documentation can be provided, the system’s efficiency may be rated lower, potentially impacting the EPC score.

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Improved floor area and insulation modelling

The update includes refined methods for calculating floor area and insulation levels, providing a more precise understanding of a home’s heat retention and energy use.

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Better treatment of flats and mid-terrace properties

RdSAP 10 adjusts how heat loss is calculated for flats and terraced homes, which were previously disadvantaged by default assumptions. This could lead to improved EPC ratings for these types of properties.