Major Changes Coming to EPC Ratings: What You Need to Know About RdSAP 10

On June 15, 2025, significant changes will be implemented to the Energy Performance Certificate (EPC) system with the introduction of RdSAP 10. This marks the most substantial overhaul of the EPC methodology for domestic energy assessments in existing homes in over a decade. The aim of these updates is to improve the accuracy of EPC ratings, better reflect how homes are actually used, and assist homeowners and renters in making informed decisions about energy efficiency. However, some Propertymark members have already reported that the more detailed assessments required may lead to increased costs. So, what exactly is RdSAP? 

Understanding RdSAP

The Reduced Data Standard Assessment Procedure (RdSAP) is the simplified methodology currently used to produce EPCs for existing dwellings. It relies on assumptions about building construction and occupancy to generate a rating of a property's energy efficiency. With the arrival of RdSAP 10, new data inputs and updated assumptions will bring EPCs into closer alignment with reality, incorporating essential structural changes.

Key Changes in Energy Assessments

1. Expanded Data Collection
   Energy assessors will now gather more detailed information about properties, including the types and conditions of glazing, heating system efficiency—backed by 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 considered if documented evidence is available. This shift places a heavier reliance on the documentation that homeowners, landlords, and agents can provide.
2. More Accurate Assessment of Heating Systems
   Historically, if the specifics of a heating system couldn’t be verified, default assumptions were used, often leading to an underestimation of efficiency. RdSAP 10 introduces a hierarchy prioritizing actual evidence over assumptions. If documentation isn't available, the system’s efficiency may receive a lower rating, potentially impacting the EPC score.
3. Improved Floor Area and Insulation Modelling
   The updated version includes refined methods for calculating floor areas and measuring insulation levels. This will yield a more precise understanding of a home’s heat retention and energy consumption.
4. Better Treatment of Flats and Mid-Terrace Properties
   Under RdSAP 10, adjustments will be made to how heat loss is calculated for flats and terraced homes, which have been previously disadvantaged by default assumptions. This could result in improved EPC ratings for these types of properties.

Implications for Agents, Landlords, and Tenants

Landlords will need to take a proactive approach to maintain and provide evidence of energy improvements. EPCs are already a regulatory requirement for rental properties, and minimum energy efficiency standards (currently set at an EPC rating of E in England and Wales) mean that an inaccurate or unexpectedly low rating could hinder tenancy opportunities. Moving forward, accurate records and receipts will be crucial—especially for insulation improvements, heating system upgrades, and double glazing installations. It’s essential that property owners keep a clear paper trail, as EPC ratings may initially drop if no supporting evidence can be provided, even if improvements have been made. We strongly encourage agents to motivate landlords to start collecting relevant documentation now in preparation for the transition.

Conclusion: A New Era of Transparency for EPCs

The upcoming changes will instill greater confidence in the accuracy of EPCs for residents. This means tenants can use this enhanced transparency to identify more energy-efficient homes, which could result in lower energy bills. Homeowners looking to sell may also benefit from a more accurate EPC to showcase energy efficiency improvements—provided they can adequately evidence such enhancements. At EPC Rating, we’re committed to keeping you informed about these significant changes. Let’s work together to ensure you’re ready as we transition into a new era for energy performance assessments!