If this relates to a live job, our heat pump survey page explains what we capture before design.
RdSAP has always used assumptions where a property cannot be fully opened up. What changed under RdSAP 10 is not that assumptions disappeared. It is that documentary evidence now matters far more often when you want a feature, upgrade, or improvement recorded with confidence rather than defaulted downwards.
Why this matters before the EPC visit
The cost of missing evidence usually appears later. A homeowner thinks the insulation, glazing, or controls will be reflected. The assessor cannot evidence it. The EPC outcome is lower than expected. Then the installer or homeowner is left arguing with a result that could have been avoided by gathering paperwork or labelled photos first.
Evidence types that often help
| Feature | Evidence that can help | What happens if it is missing |
|---|---|---|
| Insulation upgrades | Certificates, invoices, installation records, or clearly attributable documentation | The assessor may have to fall back to a less favourable assumption. |
| Replacement windows and doors | Certificates, product details, or dateable supporting paperwork | The glazing may be recorded on age-band assumptions instead. |
| Heating controls | Photos of controls plus supporting product information where needed | Controls can end up simplified or understated in the assessment. |
| Low-carbon heating and hot water equipment | Model details, commissioning paperwork, or clear photo evidence | The EPC can miss useful system detail or record it too generically. |
A homeowner checklist before the assessor arrives
- Gather any EPC, insulation, glazing, heating, or renewable-system paperwork you already have.
- If the documents are only on your phone or email, that is still usually better than nothing.
- Tell the assessor about upgrades that are easy to miss visually.
- Do not assume every improvement can be inferred just because it exists.
What installers should take from this
If an EPC outcome matters for grant routes, customer decisions, or retrofit sequencing, evidence capture has to start earlier. That may mean asking for documents before the assessor visit, photographing labels and controls properly, or keeping the paperwork with the survey report rather than chasing it later.
What RdSAP 10 still does not do
It does not remove all use of assumptions. Existing dwellings are still assessed under a reduced-data methodology. The practical aim is not perfection. It is to avoid obvious down-scoring because relevant evidence was never gathered or never kept together.
Official reference points
GOV.UK’s SAP guidance says the current RdSAP version is RdSAP 10. That is the baseline for current assessor work, even while wider EPC reform continues.
The same GOV.UK page says RdSAP assessments still use a set of assumptions about the dwelling, reducing the volume of data an assessor must collect.
Because it is still a reduced-data method, the best way to avoid weak defaults is to bring proof for the features that are easy to miss or easy to age-band incorrectly.
Sources
If you are preparing for a visit that includes EPC evidence, the EPC evidence guide is the most useful next page.