A new version of the Reduced Data Standard Assessment Procedure, RdSAP 10, was launched on 15 June 2025 and replaced RdSAP 20121. RdSAP is the methodology behind the energy performance certificates and retrofit assessments used across government energy efficiency schemes, and the change was recorded in Ofgem's delivery guidance for the Energy Company Obligation (ECO4)1.
The two published versions of that guidance give different dates for when assessments must use the new method. Version 3.2, published on 8 December 2025, states that "A new version of RdSAP, RdSAP 10, was introduced on 15 June 2025 and replaced RdSAP 2012"1. Version 4.0, published on 26 March 2026, repeats that wording and adds that "New RdSAP pre-retrofit assessments performed on or after 29 January 2026 must use RdSAP 10"2. The earlier guidance does not carry that 29 January 2026 date1.
The same guidance sets out the wider scheme rules that sit around the methodology. ECO4 places a legal obligation on energy suppliers to deliver energy efficiency measures to domestic premises, with each supplier holding a target based on its share of the domestic energy market in Great Britain, and it requires suppliers to achieve a total of £224.3 million in annual bill savings for domestic premises1. The obligation period runs from the commencement date of the ECO4 Order on 27 July 20221. Version 3.2 gives the end of that period as 31 March 2026, with measures transferable until 30 June 20261. Version 4.0 states that the document "has been updated to reflect the extension of ECO4 by nine months to 31 December 2026", with transfers until 31 March 20272.
The Warm Homes: Social Housing Fund Wave 3 guidance also records the methodology change, stating that "a new version of the methodology was launched on 15 June 2025: RdSAP 10"3. That guidance covers energy efficiency upgrades and low-carbon heating measures to homes in England, and sets out which measures can be funded3. It states that SAP-eligible technologies enabling performance and environmental monitoring, such as Smart Meter Enabled Thermal Efficiency Ratings (SMETERs), are eligible for Wave 3, but only where they form part of a technology or measure that can be modelled in RdSAP or SAP3. It adds that Phase Change Material heat batteries for hot water are not currently a formally recognised technology category in SAP, and that there is no agreed method to model their performance, so they cannot currently be installed through the scheme3.
"A new version of RdSAP, RdSAP 10, was introduced on 15 June 2025 and replaced RdSAP 2012."
Why it matters for households
RdSAP sits underneath the energy performance certificate a home receives, and that rating determines access to several publicly funded retrofit schemes. A change of methodology can therefore shift a property's assessed band, its modelled running costs and the package of measures a retrofit assessment recommends, even where nothing about the building itself has changed. The assumptions behind home energy ratings are set within the methodology, so the version in use at the point of assessment is what a household's paperwork will reflect.
For homes in scope of ECO4, the guidance ties the new method to assessment dates: pre-retrofit assessments performed on or after 29 January 2026 must use RdSAP 102. The scheme's stated purpose is delivering bill savings, and eligibility for support under ECO4 depends on the SAP band a property is placed in, with the guidance describing routes for band D and E homes to reach at least a band C, and band F and G homes to reach at least a band D1. Where a rating changes, the measures a household can be offered, and the contribution expected from the occupant, can change with it. The guidance records that since May 2024 operatives collecting customer data must input the financial amount the consumer has contributed1.
For social housing residents in England, the measures available under Wave 3 are defined by reference to what can be modelled in RdSAP or SAP, which is why some technologies are excluded until a modelling convention exists3. The regulation and policy framework around these schemes, and the official statistics that report on them, both draw on the same underlying ratings.
What happens next
Under ECO4, version 4.0 of the delivery guidance states that suppliers must meet the obligation in full no later than 31 December 2026, and that measures can be transferred until 31 March 20272. The earlier version gave 31 March 2026 and 30 June 2026 respectively1.
For the Warm Homes: Social Housing Fund Wave 3, the delivery window runs to 30 September 2028, and grant recipients may continue delivery using co-funding until March 20303. The guidance states that grant funding may be drawn down from 1 April 2025 and must be spent by 31 March 20283. It also records that domestic batteries installed alongside solar PV panels were included as an eligible measure in June 2025, that a pause on battery installations was announced in November 2025 because no Microgeneration Certification Scheme product standard was in place, and that grant recipients may resume installation of domestic batteries as of 2 February 20263. Air-to-air heat pumps are not eligible until they can be certified by MCS, which the guidance expects to happen in 20263.
Sources3 cited
- ECO4 Guidance: Delivery, ofgem.gov.uk
- ECO4 Guidance: Delivery, ofgem.gov.uk
- WH:SHF Wave 3 Scheme Guidance, assets.publishing.service.gov.uk