Spray foam and lenders
Spray foam covers the underside of the slates. What damp in the timber can the survey no longer see?
The survey can no longer see damp on the faces the foam covers. That includes the underside of the slates, any sarking against them, and the tops and sides of rafters where the foam is bonded. Staining, soft grain or a drip on those surfaces is hidden. The surveyor did not cut the foam away and did not test the timber beneath it. A dry-looking foam skin is not a dry rafter. The report can describe the foam and the wood still visible at the edges. It has not decided the concealed timber is sound.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
From a loft, roof timber is normally judged by looking at rafters and the underside of felt or a membrane. Spray foam closes that view. A leak can stay masked until water shows at a junction the foam does not cover, such as a wall plate or a valley. Foam can also hold moisture against wood so decay advances out of sight. This visit did not separate those mechanisms and did not sample the foam. Hidden timber has not been cleared, and it has not been condemned.
Tell your solicitor, and a lender if one asks, that part of the roof structure is concealed. Some lenders want more information where spray foam is present. The survey has not removed it and has not priced a repair. If the timber must be known, a specialist has to expose representative areas, which is outside this report. Ask the seller for any warranty and for photographs taken before the foam went on. Those papers still do not show the wood as it is now.
What should you ask your surveyor?
- Which rafters, if any, can still be seen at the eaves or beside a party wall?
- Does the report say the foam is bonded to the slates, or only to a membrane?
- Are there drip stains on timber that remains visible beyond the foam?
What are the typical next steps?
- Read the roof section as a limited inspection, not as a clean result for the rafters.
- Ask the seller for the foam warranty and any photographs from before installation.
- If the timber must be proved, instruct an exposure this survey did not make.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Does foam on the slates mean the roof timber is damp?
No. Foam is a covering, not a diagnosis. It stops the survey seeing the timber, which is different from proving decay. Some roofs under foam are dry and some are not. This visit could not tell which, because the faces that would show damp were hidden. Do not turn a limit on inspection into a finding of rot.
Can you peel a corner of the foam back to help the next inspection?
Do not. Cutting or peeling spray foam can damage the covering, the timber and the product, and it is not a controlled inspection. The surveyor left it in place for that reason. If an area must be exposed, agree who does it and how it is made good. A casual tear is not evidence you can rely on.