RdSAP is the reduced-data version of SAP used to assess existing homes; BRE maintains it for government BRE. Version 10 went live for new assessments on 15 June 2025 Elmhurst RdSAP 10. It is the biggest revision the survey methodology has had: less assuming, more measuring.
What changed
- Windows are measured, not assumed. Assessors record each window rather than defaulting glazing areas from the property's age band Elmhurst RdSAP 10.
- Ventilation counts. Mechanical and natural ventilation are modelled in detail, and air pressure test results can be entered Elmhurst RdSAP 10.
- More room-in-roof and fabric data. Additional data items capture the awkward geometries older homes actually have Elmhurst RdSAP 10.
- Evidence gates the inputs. Features that cannot be seen or documented fall back to conservative defaults. Your cavity insulation without paperwork may as well not exist, as far as the model is concerned.
Why a renewal can score LOWER
Same house, new methodology, different number. Sometimes a lower one.
Old certificates leaned on age-band assumptions that were often generous. Re-assess the same house under evidence rules and undocumented features stop scoring, while measured windows and ventilation replace favourable defaults. A marginal E can re-emerge an F, and a marginal C a D, without a brick changing.
This cuts both ways: a well-documented house with genuine improvements can score higher under RdSAP 10 than its lazy old certificate. The variable is evidence. The RdSAP 9 vs 10 comparison works through a same-house example input by input.
What householders should keep
Boiler installation and service records, insulation invoices and guarantees, window installation certificates, solar and battery paperwork, any air pressure test. File them where the next assessor can see them; the assessment walkthrough shows where each document lands in the survey.
Where this sits in the bigger churn
RdSAP 10 is the current methodology, not the destination. The certificate itself is being reformed around four metrics, and the calculation engine is scheduled to hand over to the Home Energy Model. If your certificate is still valid, the renewal timing question is real: should I renew my EPC now has the decision table, and the reform tracker has the dates.