Spray foam and lenders

What is the difference between open-cell and closed-cell spray foam under a roof?

Open-cell foam is softer and more vapour-open. Closed-cell foam is rigid and far less vapour-open, and it is the type that most often sticks to the underside of a covering and hides the timbers. RICS says some spray foam makes it difficult to see roof problems from the loft. The names do not tell you whether this installation is acceptable to a lender.

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?

The RICS consumer guide on spray foam tells buyers to check the paperwork and to ask the mortgage provider whether the lender’s policy allows the product. It does not split that advice into a pass for open-cell and a ban for closed-cell. Either type can be installed badly, block ventilation, or conceal a leak that then rots timber. A surveyor may be able to say which type it looks like. They cannot peel it off to inspect the rafters as part of a normal visual survey.

Ask the seller for the specification, not just the word “foam”. If the paperwork is missing, the RICS guide is frank that documentation is what valuers, lenders and solicitors ask for. This page does not say every lender refuses every foam. It says you must ask the lender you are actually using.

What should you ask your surveyor?

Can you tell whether this foam is open-cell or closed-cell, or not?
Can you see the rafters and the underlay, or has the foam hidden them?
What paperwork would you want the seller to produce for a lender?

What are the typical next steps?

Ask the lender’s policy in writing before you argue with the seller about removal.
Ask the seller for the installer’s specification, guarantee and any product certificate.
Do not scrape a patch off to identify the foam. You may damage the covering and still not satisfy the lender.

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

Is open-cell always acceptable?

No. RICS does not give it a free pass. The lender and the condition of this roof decide, not the adjective.

Can a surveyor see rot behind closed-cell foam?

Often they cannot. The guide warns that hidden leaks can rot timber. Absence of a rot comment may only mean the timber could not be seen.