Independent UK guide · Last reviewed: 6 October 2026
Spray foam insulation problems: damp, rot, mortgages and what to do
Quick answer
The main problems with spray foam insulation in a UK roof are that it can trap moisture against the roof timbers, it hides those timbers so a surveyor cannot inspect them, and many mortgage and equity release lenders decline homes that have it. Not every installation causes damage, but most make a sale or remortgage harder.
We are an advice and referral service. We do not carry out removal: vetted removal companies we introduce survey, quote and do the work. Written by the Spray Foam Removal Advice editorial team.
The problems
What are the main problems with spray foam insulation?
Around 250,000 UK homes are estimated to have spray foam insulation. Most of the problems below concern foam sprayed onto the underside of a pitched roof, which is where it is usually found in UK lofts.
1. Moisture trapped against the roof timbers
A traditional loft is draughty on purpose: moving air carries moisture away. The RICS consumer guide to spray foam insulation explains that spray foam creates a warm roof void that seals gaps to keep heat in, but “will also seal in moisture unless adequate precautions are taken”. The Property Care Association (PCA) says the result can be condensation, especially in cold weather, leading to timber decay, mould and corrosion of metal fixings. So yes, spray foam can cause damp, and damp timber can rot. The foam does not rot wood by itself; persistent moisture does. More detail: how spray foam can lead to hidden timber rot.
2. The timbers and roof covering cannot be inspected
RICS states that a timber roof structure covered with spray foam “cannot be fully seen or inspected”, and that a roof leak behind some types of foam may go unnoticed until timber is already rotting. This is the problem that drives most of the others: a surveyor cannot confirm the rafters are sound, so cannot rule out a defect. It also makes ordinary roof repairs harder, because slipped tiles and failed felt are hidden from inside.
3. Mortgage, sale and equity release refusals
RICS says spray foam “could affect a surveyor’s professional opinion of value” and that a surveyor who finds it may ask for an independent specialist report. The PCA records that surveyors’ concerns have led “certain mortgage companies” to refuse to lend. By our own estimate, around 70–80% of the UK mortgage market declines outright on homes with spray foam, while a smaller number of building societies and specialist lenders will consider an application with conditions. In practice that means fewer buyers who can borrow, and sales that fall through at valuation. See which mortgage lenders accept spray foam and selling a house with spray foam insulation.
4. Reduced roof ventilation
RICS notes that most pitched roofs on houses and bungalows are designed to be ventilated, and that spray foam is a change to that original design. Some products need a dedicated ventilation channel behind the foam and must not be sprayed against the roof underlay at all. Where foam has been applied straight onto felt, tiles or slates, blocking the eaves, the airflow the roof was built to rely on is gone. Our guide to spray foam roof insulation problems covers this in more depth.
5. Poor installation
Many problem lofts were sold on the doorstep. The PCA says improper installation “can significantly increase the risk of problems”, including overspraying, the wrong type of foam and the wrong thickness. RICS advises homeowners not to accept cold-call or unsolicited offers of spray foam, and to keep the installation contract, calculations, any guarantee and any independent test certificate. Missing paperwork is a problem in its own right, because it is the first thing a valuer or lender asks for.
6. It is difficult and costly to take out
RICS describes spray foam as a permanent installation that is “not considered reversible”, because removing it could damage the existing structure. The PCA calls removal “a complex and expensive process” needing specialised equipment. Professional removal typically costs £50–£80 per m², or about £3,000–£8,500 for most lofts, and takes 2–5 days for a typical three-bedroom home.
Foam type
Are the problems different for open-cell and closed-cell foam?
Yes. Both hide the timbers, but they behave differently with moisture and they come out differently. The PCA singles out closed-cell foam as the type most likely to form a barrier that traps moisture in the roof.
| Feature | Open-cell | Closed-cell |
|---|---|---|
| What it is | Soft, light and sponge-like; can be compressed by hand | Rigid and dense; hard to the touch |
| Typical problem | Hides the timbers and can hold moisture against them if the roof leaks or is poorly ventilated | Forms a barrier that can trap moisture in the roof, and bonds hard to timber, felt and tiles |
| Removal difficulty | Lower: usually quicker to strip | Higher: slower, with more risk of disturbing the roof covering |
| Typical removal cost | £50–£65 per m² | £65–£80 per m² |
Removal guides for each type: open-cell spray foam removal and closed-cell spray foam removal. If you do not know which you have, a removal company can usually tell from photographs or the original paperwork.
Checking your own loft
How can you tell if your spray foam is causing a problem?
You often cannot tell from a quick look, which is the difficulty. RICS warns that with foam in place “you may not see a problem developing until it is too late”. These checks are a starting point, not a substitute for an inspection.
Signs you can look for yourself
- A musty or damp smell in the loft that was not there before
- Dark staining or damp patches on any timber still visible, such as purlins or rafter ends
- Water droplets or wet patches on the surface of the foam in cold weather
- Foam that has cracked, shrunk or pulled away from the rafters, leaving gaps
- Foam sprayed directly onto tiles or slates, with no felt or membrane between
- Stains on bedroom ceilings, or tiles that have slipped outside
More on each: seven signs your spray foam is causing problems. Do not cut or pull foam away to look behind it.
What a surveyor looks at
- How much of the roof structure can be seen at all
- Whether the foam looks open-cell or closed-cell, and how well it is bonded
- What the foam was sprayed onto: felt, a breathable membrane, or the tiles themselves
- Whether the roof is still ventilated at the eaves and ridge
- Moisture readings in any timber that can be reached
- The paperwork: contract, product certificate, guarantee and photographs
In March 2023 the PCA and the Residential Property Surveyors Association published an inspection protocol for sprayed foam in domestic roofs, written to help surveyors identify roofs where the risk of decay has not been significantly increased.
A fair answer
Is all spray foam insulation a problem?
No. Properly specified, correctly installed and fully documented spray foam exists, and it does not all cause damp or rot. The Insulation Manufacturers Association stated in February 2026 that spray foam “is safe and rarely needs to be removed if it has been installed correctly”, and warned about businesses contacting households to say any spray foam should be inspected or removed. The PCA and RPSA protocol exists precisely so that good installations can be recognised.
Two things remain true even for a sound installation. The timbers are still hidden, so the next surveyor still cannot see them. And the lending decision belongs to the lender: many decline spray foam as a matter of policy, whatever the condition of the roof. So the practical question is rarely “is my foam bad?” and more often “what has my lender, buyer or surveyor asked for in writing?”
If your main worry is health rather than the building, read is spray foam insulation safe?
Next steps
What should you do if you have spray foam insulation?
- 1
Find your paperwork
Installation contract, product name, any BBA or Kiwa certificate, guarantee and photographs. RICS says a valuer, lender or solicitor may ask for all of it.
- 2
Ask for the requirement in writing
If a lender, buyer or surveyor has raised the foam, ask exactly what they need: an inspection report, removal, or removal plus a certificate.
- 3
Get an independent inspection if nobody has asked yet
If you are concerned about your foam, the Insulation Manufacturers Association suggests having the installation inspected by a qualified RICS chartered surveyor.
- 4
Price removal properly
Removal typically costs £50–£80 per m², about £3,000–£8,500 for most lofts. Compare more than one quote and check waste, report and VAT are included.
- 5
Leave the foam alone in the meantime
Cutting or scraping it yourself creates dust, can damage felt and timber, and leaves no paper trail for a lender.
- 6
Keep the evidence
Before and after photographs, the invoice and any removal report belong in one folder for the next sale or remortgage.
Useful next reads: RICS surveys and spray foam, spray foam removal cost per m², spray foam removal certificates and why DIY spray foam removal goes wrong.
Common questions
Spray foam insulation problems: FAQs
Call the team on 03330 908 569 to talk through your own loft.
Why is spray foam insulation a problem? +
Because it covers the roof timbers so they cannot be inspected, it can seal moisture into the roof, and many lenders decline homes that have it. The foam may be insulating well and still stop a sale or remortgage.
Does spray foam insulation cause damp? +
It can. RICS says spray foam seals in moisture unless adequate precautions are taken, and the Property Care Association says the result can be condensation in the roof, especially in cold weather. A correctly designed and ventilated installation is less likely to cause damp.
Does spray foam rot wood? +
Not directly. Timber rots when it stays damp. Spray foam can hold moisture against rafters and can hide a roof leak, so decay may go unnoticed for longer than it would in an open loft.
What are the problems with spray foam roof insulation and loft insulation? +
In a loft the foam is normally sprayed onto the underside of the roof slope. The usual problems are hidden rafters, reduced ventilation, trapped moisture, foam bonded to felt or tiles, and lender refusals. Foam on the loft floor is uncommon in the UK.
What is wrong with spray foam insulation for mortgages? +
Valuers cannot inspect the roof structure, so many lenders will not accept the risk. By our estimate around 70–80% of the UK mortgage market declines outright; some building societies and specialist lenders will consider a case with conditions.
Are there issues with every spray foam installation? +
No. Correctly specified, installed and documented foam does not necessarily damage a roof, and the Insulation Manufacturers Association says it rarely needs removing if installed correctly. The timbers are still hidden, though, and a lender may still decline.
Can spray foam problems be fixed without removing it? +
Sometimes an independent inspection report is enough for a lender or buyer. Where the foam is trapping moisture, or a lender requires the timbers to be visible, removal is usually the only route. Ask for the requirement in writing first.
How much does it cost to fix spray foam insulation problems? +
Professional removal typically costs £50–£80 per m², which is about £3,000–£8,500 for most UK lofts. Open-cell foam is usually £50–£65 per m² and closed-cell £65–£80 per m². Timber repairs and re-insulation are extra.
Sources
- Spray foam insulation: consumer guide — Royal Institution of Chartered Surveyors (RICS)
- Sprayed foam in roofs: advice for homeowners — Property Care Association
- Sprayed foam insulation in domestic roofs, including the March 2023 inspection protocol — Property Care Association
- IMA statement on spray foam, February 2026 — Insulation Manufacturers Association
Prices, the estimate of homes affected and the share of the mortgage market that declines are our own editorial figures, not statements by the bodies above. Lender policies change; check your own lender’s wording.
Last reviewed: 6 October 2026 · Spray Foam Removal Advice editorial team
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