The way we measure energy efficiency in UK homes is about to undergo its most significant transformation in over a decade. On 15 June 2025, the new RdSAP 10 (Reduced Data Standard Assessment Procedure) methodology officially went live, replacing the ageing RdSAP 9.94.+1
For homeowners, landlords, and estate agents, this is not just a technical update for assessors; it is a fundamental shift in how properties are valued, marketed, and improved. At First Certify, we want to ensure you are ahead of the curve. Here is everything you need to know about the transition to RdSAP 10.
What is RdSAP 10?
RdSAP is the “engine” used to produce Energy Performance Certificates (EPCs) for existing dwellings. While the full SAP 10.2 is used for new builds, RdSAP 10 is the streamlined version designed for existing homes where full technical data might not be available.+1
The goal of version 10 is simple: Accuracy. By moving away from “default assumptions” and requiring more evidence based data, the new EPCs provide a much more realistic picture of a home’s actual energy performance.
5 Major Changes You Need to Know
1. Mandatory Window Measurements
Previously, assessors only measured “atypical” windows, relying on software assumptions for the rest based on the age of the property. Under RdSAP 10, every single window must now be measured individually. Assessors also record the orientation, frame type, and even the presence of permanent shutters.+1
- The Impact: This provides a far more precise calculation of heat loss, which is often the biggest factor in a home’s efficiency.
2. Better Recognition of Low Carbon Tech
The old system struggled to accurately account for modern green technologies. RdSAP 10 finally brings these into the spotlight.
- What is included: Battery storage systems, PV diverters (which use excess solar power to heat water), and heat pumps are now better recognised.
- The Benefit: If you have invested in renewables, your EPC rating is now more likely to reflect that value.
3. Refined “Room in Roof” Categories
Assessors now distinguish between a “true” room in the roof and those with “common walls” (essentially a short additional storey).
- The Impact: This eliminates the “one size fits all” penalty that often lowered the score of loft conversions.
4. The Power of Evidence (No more guessing)
RdSAP 10 moves heavily towards a “hierarchy of evidence.” If an assessor cannot see it or you cannot prove it with paperwork, the software will default to a lower performance value.
- The Strategy: Having your boiler service records, insulation certificates, and window warranties ready for your First Certify assessor is now more critical than ever to protect your rating.
5. Air Pressure Test Integration
For the first time, if you have had a professional air tightness or “blower door” test, the actual results can be entered into the EPC software.
- The Impact: Proving your home is draught free can often boost your score by several points, potentially pushing a property from a D to a C.
What This Means for You
| Stakeholder | Key Takeaway |
| Homeowners | Your assessment will take longer (usually an extra 20 to 30 minutes) as the assessor gathers more data. |
| Landlords | Accurate EPCs are vital for meeting Minimum Energy Efficiency Standards (MEES). The new detail helps you target retrofits more effectively. |
| Estate Agents | You can now market “verified” energy efficiency with more confidence, especially for homes with heat pumps or solar batteries. |
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Prepare for Your Assessment with First Certify
The move to RdSAP 10 is a positive step toward the UK’s Net Zero goals, making EPCs a more reliable tool for everyone. However, because the assessments are now more detailed and time intensive, it is important to choose an accreditation partner that understands the new conventions inside out.
At First Certify, our team are fully trained and equipped for the RdSAP 10 era. We ensure your property is assessed fairly, accurately, and with a focus on highlighting the genuine improvements you have made.
Is your current EPC reaching its 10 year expiry? Book your RdSAP 10 compliant assessment with First Certify today to ensure your property’s rating is accurate for the 2026 market.
