Supply Chain Advice Pack: RdSAP Changes for the Supply Chain (RdSAP v.10)
Introduction
Reduced Data Standard Assessment Procedure (RdSAP) is the official method for producing standards and Energy Performance Certificates (EPCs) for existing properties. Full SAP is the version used for new builds. It is a software tool used to calculate a new building’s predicted energy use by using standard values. An energy assessor or surveyor collects data on site and enters this into the software.
Published: May 2025
Contents
Overview
The current version is RdSAP 2012 however, after several delays, the government has announced that RdSAP 10, will be released in 2025 and Industry bodies have reported that the standard is expected to launch on 15th June 2025.
This advice pack provides information on the changes to RdSAP, and what that means for the supply chain following its adoption.
Aims of changes
- 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. This will allow homeowners and landlords a better idea on the effectiveness of insulation, heating systems and energy performance assessments.
- 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.
Summary of changes
RdSAP v.10 is the only methodology that can be used to demonstrate compliance with Part L of the Building Regulations 2021. These changes align to an improved ‘Notional’ Building (a hypothetical target for a property, identical to the one receiving works, to use as comparison), this considers some of the key changes from previous versions as follows:
Measurement changes:
- Measurements for all windows required. More accurate calculation for hot water consumption and lighting energy.
Additional technologies:
- Window shutters added as a new feature.
- Hot water tank size included.
- Hot water tank insulation included.
- Inclusion of heat interface units, new heating controllers, and additional fuels in the PCDB.
- PV Diverter for water heating added.
- PV Batteries added.
Other revisions:
Energy and Emissions:
- Updated fuel prices and CO2 emissions with monthly variations.
- Revised self-use factor for PV systems, considering battery storage and PV diverters.
Heating and Ventilation:
- Revised distribution loss factors for communal heating networks.
- Updated chimney and flues air flow rates.
- Revised treatment of mechanical ventilation system heat recovery and performance.
- Adjusted the assumed standard heating pattern.
Building Characteristics and Data:
- Updated reference building characteristics.
- Infiltration rate calculation includes low pressure pulse testing results.
- Removal of summer gains check (Appendix P).
Efficiency and Recovery Systems:
- Wastewater heat recovery system efficiency varies with shower flow rate.
Impact on the supply chain
The changes to RdSAP will have an impact throughout the supply chain for manufacturers, distributors, installers and end users as well as compliance and regulators.
The upcoming changes to RdSAP methodology will have the following impact:
More accurate assessments: The new RdSAP 10 will require 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.
Optional Air Tightness Testing: RdSAP 10 allows, but does not require, DEAs to input the results of an air pressure test, also known as an air tightness test. This will enable a more accurate assessment of a property's energy performance.
New age bands: New age bands for properties built after 2023 will be used to show improvement in u-values, emphasising the importance of data management and build dates.
Increased focus on heat pumps: The demand for heat pumps is likely to increase, due to the new methodology often favouring their use where properties are already well insulated.
Inclusion of PV diverters and battery storage: Assessors will now account for PV diverters and battery storage where present. Due to increased efficiency of solar panels for the homeowner, diverting them towards a specific load or appliance. This increase in efficiency is likely to see an increased demand in this technology.
Impact on future government funding schemes: The changes to RdSAP are likely to affect the eligibility for future government schemes, therefore it is important contractors involved in these schemes comply with the new assessment criteria.
Detailed product specification: RdSAP will include more detailed assessment criteria to provide a clearer picture of a home’s energy related features, including more detailed assessment criteria for roof rooms, distinguishing between different types and requiring specific data for each element. It also requires more detailed inputs for ventilation systems and renewable heating technologies, reflecting advancements in these areas.
Product demand and distribution: Due to the nature of the updated methodology, certain products such as heat pumps will see an increased demand, which may cause an increase in cost until the supply chain catches up with the demand.
The upcoming changes to RdSAP methodology will impact installers in the following ways:
- Product demand: Due to the increased product demand, products such as heat pumps will need to be procured/ordered early, to reduce the risk of bottlenecks when it comes to delivery.
- Training and certification: Additional training and certifications may be required for installers, in line with new RdSAP requirements.
- Inventory management: Installers will have to ensure that work complies with the new RdSAP requirements by updating practises and procedures to align with project requirements.
Best Practice
To keep on top of the upcoming changes, it is important to ensure you are prepared and proactive. There are several ways to ensure that the changes don’t catch you by surprise. You can:
- Stay informed: check the BRE website and accreditation bodies for updates.
- Training and certification: Ensure your team are up to date with the relevant training. Certified assessor roles may need to complete specific refresher training.
- Use updated tools: Make sure you are using appropriate up-to-date software to be more accurate and efficient.
- Communicate with clients: Ensure you maintain an open conversation with your clients, keeping them informed on how the changes may affect them.
- Review processes: Now is a great time to review and adapt your processes to ensure they meet the new standards.
- Target/ milestone setting: Set out where you want to be, by when.
Requirements of RdSAP in Warm Homes
With the upcoming 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.
You should also view the latest guidance online as it can be updated regularly but note some of the key points from the Warm Homes guidance dated April 2025:
- The EPC Accreditation companies have indicated that retrofit assessments will not be permitted to take place in RdSAP 2012 after RdSAP 10 is in place.
- EPC Accreditation companies have instead indicated that they will continue allowing the generation of RdSAP 2012 post-retrofit Energy Performance Reports (EPRs) to enable retrofits that started in RdSAP 2012 to be completed in RdSAP 2012, where the pre-retrofit assessment took place before the “go-live” date of RdSAP 10. In these situations DESNZ will accept an EPR being generated, and an Energy Performance Certificate (EPC) will not be required.
- Any new projects that start after the RdSAP 10 “go-live” date will be required to be fully assessed in RdSAP 10 to be Trustmark compliant.
It is also worth noting, that Lead Applicants will be required to set out the projected energy savings, which must be based on modelling via the current SAP, RdSAP or Passive House Planning Package (PHPP) methodologies.