What building owners need to know about changes to EPCs

Changes to the way Energy Performance Certificates (EPCs) are calculated for the UK’s 27 million existing homes were officially rolled out by the government on 15 June 2025. The new standard not only impacts building owners, such as commercial and social landlords, but also homeowners. These changes represent the most significant update in nearly 20 years to the calculation and default values within the Reduced Data Standard Assessment Procedure (RdSAP) which produces the EPC Bands of A to G we are all familiar with. 

Why it matters

Government figures show emissions from residential buildings accounted for 20% of greenhouse gas emissions in the UK. For some time there has been a call for domestic energy performance calculations to be updated to better reflect how our existing homes perform. The introduction of RdSAP10 comes as part of the UK’s broader aim to achieve net‑zero emissions and high energy‑efficiency standards. By requiring more rigorous, evidence‑based data from assessors, RdSAP10 aims to:

• Improve accuracy of EPC ratings
• Ensure homes bought, sold, or rented reflect real-world performance
• Better inform retrofit decisions and grant funding allocations  

Crucially for the building’s owner, this can influence resale value, funding eligibility, and compliance.

How the RdSAP is changing

When an assessor carries out an energy assessment, they will be required to accurately collect a broader set of property information, such as:

• Every window will be measured, including the orientation, frame, glazing type/gap, age, draught proofing, and if any shutters are installed.
• Room‑in‑roof spaces require greater detail, with two new room types and additional measurements of gable and party walls.
• Wall insulation measurements are more precise, increasing in 25 mm increments, and permitting minimum values and custom thickness if needed.
• Ventilation information is increased to account for fireplaces, flues, mechanical systems, and chimneys to aid the understanding of air permeability.
• The increase of domestic basements is recognised, which will require more detailed inputs.

Whilst this increase in the data is welcomed to improve accuracy, the additional time spent capturing the data will result in longer survey visits and increased costs. These have been estimated at between £10 and £30. Whilst this is notional to a homeowner’s overall selling fees, the impact will be greater for commercial and social landlords with residential portfolios in the 10,000s. 

Evidence‑led vs. default assumptions

A fundamental change under RdSAP10 is the shift in emphasis on documented evidence. Property owners will be permitted to provide receipts and/or specifications to verify the standards for insulation, windows and renewables. New EPCs will reflect all verified improvements. This is of particular note for advances in heating systems performance and smart controls which will enable the assessor to override the conservative defaults values.

Aligning existing residential property and new build assessments, an air pressure test will now be allowed. It is estimated that excellent airtightness can boost EPCs by 1–3 points or even a band. For the first time, this offers commercial property owners an extremely cost effect method of increasing their portfolio’s energy performance, with minimal disturbance to the occupier.  

Winners and losers

Inevitably, there are both winners and losers as a result of the updated calculation methodology. Homes benefiting from retrofitting low-carbon technologies, such as PV, heat pumps, and battery storage, may be rewarded with EPC increases. Owners of flats and mid‑terraced homes will benefit from better heat-loss modelling. Addressing air tightness and evidencing well-sealed older homes will overcome poor default air pressure values.

Property owners who are not able to provide documentation for works carried out and homes with outdated heating and hot water systems may see their performance fall. 

As the clock ticks ever faster towards the government’s target of all social housing achieving EPC Band C by 2030 and the UK housing stock being decarbonised by 2050, these changes should be welcomed as a science led step in the right direction.