RdSAP10: A Must-Read for Retrofit Projects

Understanding the New RdSAP10 – What Rural Housing Providers Need to Know

If you are involved in managing housing stock, planning retrofit projects, or working towards improving energy performance across rural homes, you need to be aware of important updates to the way Energy Performance Certificates (EPCs) are calculated.

On 15th June 2025, the Government released a new version of the Reduced Data Standard Assessment Procedure (RdSAP), the methodology that underpins all domestic EPC ratings in the UK. These changes are particularly relevant for any housing providers aiming for EPC Band C or delivering schemes like the Warm Homes programme – where EPCs and RdSAP play a central role in compliance and funding eligibility.

RISE – the free support service funded by the Department for Energy Security and Net Zero – have put together a comprehensive explainer to help housing professionals and retrofit businesses understand the updates, navigate the changes, and ensure future plans are aligned with RdSAP10 requirements.

We are pleased to share their guidance below in full.

Energy Performance Certificates (EPCs) are a widely known feature of building management; often used as a shorthand for a building’s energy efficiency.

A lesser known, but just as critical part of the picture is the Reduced Data Standard Assessment Procedure – or RdSAP. RdSAP is the method through which a building’s energy efficiency is calculated, and it forms the basis for producing all EPC ratings.

An accurate RdSAP leads to an accurate EPC, which in turn ensures that housing providers can make the best decisions about refurbishment, retrofitting, and energy upgrades. And as government-funded retrofit schemes like Warm Homes are tied to EPC ratings, a full understanding of RdSAP helps housing providers prioritise work and unlock funding.

On 15th June 2025, an updated version of RdSAP was published, with a range of changes and improvements made. The changes are significant, focused on accuracy, relevancy and detail – and having a full understanding of the new process is essential for anyone planning or developing a domestic retrofit project.

• More accurate assessments: RdSAP 10 will require more actual measurements rather than relying on assumptions, as well as having better categorisation and efficiency measurements for different types of heating systems.
• Integration of renewable technologies: The new version will offer a more comprehensive assessment of homes using renewable energy technologies.
• New age bands and regions: The introduction of new age bands (properties built from 2023 onwards) and new regions will make the assessments more relevant and granular.

Key changes from previous versions include:

• Measurement changes: Measurements for all windows now required. More accurate calculation for hot water consumption and lighting energy.
• Additional technologies:
• Window shutters have been added as a new feature
• Hot water tank size and insulation are now included
• There is now inclusion of heat interface units, new heating controllers, and additional fuels in the PCDB
• PV Diverter for water heating and PV batteries have now been added

Further revisions include updates across several areas. For example, energy and emissions now reflect monthly fuel price and CO? emission variations. Heating and ventilation changes include revised distribution loss factors for communal heating networks and updated chimney and flues air flow rates. Building characteristics now incorporate updated reference building characteristics, the infiltration rate calculation now includes low pressure pulse testing results and there has been the removal of summer gains check.

With the Warm Homes schemes, RdSAP will be a key component for various elements of policy. For example, when calculating performance metrics such as EPCs, RdSAP will be used. Also, measures regarding energy performance or heating that are allowed under the WH:LG and WH:SHF must be compatible with the latest version of RdSAP at the time of delivery.

In particular, PV batteries – a type of battery storage installed to work alongside solar PV panels – have now become an eligible measure under the Warm Homes: Social Housing Fund and Warm Homes: Local Grant schemes, because PV batteries have also been integrated into RdSAP (it should be noted that PV batteries can only be installed under the Warm Homes schemes where it complements existing or new Solar PV).

The changes to RdSAP also impact throughout the supply chain for manufacturers, distributors, installers and end users as well as compliance and regulators, across a range of areas. For example, the new procedure now requires more accurate assessments throughout. For example, windows will require exact measurements for each opening, including details about frame type and solar transmittance rather than relying on assumptions as per previous versions. The increased focus on heat pumps with the new RdSAP (favouring their use where properties are already well insulated) will most likely see demand for this type of technology increase, affecting supply and cost. And as RdSAP now includes a more detailed assessment criteria to provide a clearer picture of a home’s energy-related features, pressure increases on suppliers to rise to this standard.

RISE (the free support service funded by the Department for Energy Security and Net Zero to support social housing providers, local authorities and their supply chains plan and deliver successful domestic retrofit programmes) has produced a range of materials to walk housing providers and retrofit businesses through these changes to RdSAP. Through Masterclasses, advice packs and direct support, RISE breaks down the changes to the procedure, explains why these matter to providers and how they can respond to the changes.

RISE is here to help housing providers and their supply chains get up to speed with RdSAP10, with a range of resources to help:

Download the full RDSAP10 Advice Pack for suppliers here (RISE website).

Follow the RISE YouTube channel, to watch recent Masterclasses on RdSAP delivered by the RISE team (RISE YouTube channel)