Surveys and foam
Why can't a surveyor see my roof timbers?
The short answer
Because spray foam covers them. Once foam coats the underside of the roof, the rafters, battens and felt sit behind a solid layer, and a surveyor working from the hatch can neither see nor probe the wood. The report will say so, and may suggest a specialist look. A roofer can open the foam in a few places and test the timber directly.
A home survey stops at the surface. When the surface is foam, the roof structure goes unseen. Here is what that means if you are buying or selling.
What a surveyor reaches from the hatch
A home survey is a visual inspection. The surveyor looks into the loft with a torch, notes what is exposed, and reports on what can be seen from where they stand. They do not lift boards, cut into insulation or strip finishes, and they leave stored belongings where they are.
In an ordinary loft that is plenty. They can see the rafters, the underside of the felt, any staining and the state of the insulation on the floor, and a moisture meter or a probe may be used on exposed wood. In a foamed loft the same visit shows a pale or yellowish surface where the roof structure should be. The timbers are somewhere behind it.
None of this is a failing on the surveyor's part. The inspection is limited by what they are allowed to disturb, and cutting holes in someone else's insulation falls outside it. They report the limit, and the limit travels with the report to the buyer and the lender.
How foam shuts the structure away
Foam on the underside of a roof coats the rafters, fills the spaces between them and often climbs over the wall plate. The wood vanishes from view the way a wall vanishes behind plaster. You may see the line of a rafter as a ridge in the surface, but not the state it is in.
That matters because the problems that count are on the hidden side. Staining, soft wood and mould live on the faces of the timber and on the felt, and the foam is in the way. RICS lists dampness, uncontrolled condensation especially, among the dangers of insulation that has been fitted badly, in its March 2023 consumer guide for owners.
The same guide treats spray foam as something that may influence a surveyor's professional opinion of value. A surveyor who cannot see the timbers therefore has two reasons to mention foam in the report, one about what lies hidden and one about worth.
What the report is likely to say
Expect the loft paragraph to name the foam, say the roof timbers were out of reach, and suggest a further look from a suitable specialist. The wording differs between firms. What it means for you does not: the surveyor has told your buyer or your lender that the wood is unverified.
Lenders have not settled on one line. Reporting in November 2024 showed some refusing homes with foam outright and others judging each case. Because a lender sees the report, or a digest of it, a note about foam can find its way into the mortgage offer. Our guide to spray foam and mortgages gathers the public statements lenders have made.
A line like this is not a verdict on the roof. It records an absence of evidence, and absence of evidence can be remedied by going and looking, which is the next step in most sales.
Getting the timbers looked at
A roofer can supply what the surveyor could not. One of us goes up with a camera, records the foam as found, and cuts small windows in it, mostly at the eaves and low on the rafters, where water tends to settle. A thin probe goes into the wood at each opening. Sound timber resists and feels dry, while softened timber lets the point sink.
The roof is inspected from outside too, looking for slipped tiles, failed flashings and anything else that might let water in. The findings, with pictures, are sent with the written quote, a single total for whatever work we recommend.
The openings are small and are made good afterwards. They are a sample, not a check of every rafter, and our report says where the wood was tested. Our answer on what to do when a survey finds spray foam walks through the usual order of events.
What buyers and sellers do next
If you are selling, getting the roof tested before the buyer's survey puts evidence on the table in place of a question mark. If you are buying, ask the seller whether any roofer's report exists, and whether the foam was fitted with paperwork you can see.
Three outcomes are common. The checked timber proves sound and the foam stays, with the report kept on file. Part of the foam is opened and the rest is left. Or all of it comes out and the roof is put right. Which of them makes sense depends on the photographs, the buyer and the lender, and it is a conversation between you, your solicitor and your mortgage adviser.
Our guide to selling a house with spray foam covers the paperwork that helps, and the spray foam insulation removal page explains the service we offer.
Related questions
Surveyors and foam
Does a roofer's report replace the surveyor's?
No, it adds to it. The surveyor's report stays as it is. A roofer's photographs and timber findings can be handed to the buyer, the lender or the surveyor as further evidence, and they decide what weight to give it.
Who pays for the foam to be opened during a sale?
That is for the buyer and seller to agree, usually through their solicitors. Opening a few small sections costs far less than a full removal, and many sellers arrange it so the evidence exists before the buyer's survey takes place.