| Input | RdSAP 9 (to Jun 2025) | RdSAP 10 (from 15 Jun 2025) |
|---|---|---|
| Windows | Glazing area assumed from the property's age band | Each window measured and recorded Elmhurst RdSAP 10 |
| Ventilation | Coarse defaults | Mechanical and natural ventilation modelled in detail Elmhurst RdSAP 10 |
| Airtightness | Not enterable | Air pressure test results can be entered Elmhurst RdSAP 10 |
| Room in roof | Simplified treatment | Additional data collected on site Elmhurst RdSAP 10 |
| Undocumented features | Often credited via age-band assumptions | Fall back to conservative defaults without evidence |
| Survey time | Shorter walk-round | Longer: more measurement and evidence collection Elmhurst RdSAP 10 |
The same-house example, worked in words
Take the 1930s semi with cavity walls filled in the 1990s, paperwork long gone. Under RdSAP 9, the age band and a visual once-over could credit the insulation, and glazing was assumed typical for the era. Under RdSAP 10 the assessor measures the actual windows (larger single-aspect glazing than the age-band average: points down), and the undocumented cavity fill drops to a conservative default (points down again). Same bricks, lower number. Reverse the story for a documented, genuinely improved house: measured reality beats a stingy assumption, and the score rises.
Does my RdSAP 9 certificate remain valid?
Yes. Certificates are valid for 10 years under the methodology that produced them; nothing about the version change voids existing EPCs Elmhurst RdSAP 10. The practical consequence is only at renewal, which is exactly why renewal timing is now a decision: see should I renew my EPC now, the fuller RdSAP 10 page, and what the assessor does on site.