The number of UK households with spray foam insulation in their lofts has doubled since 2015, but so have the number of mortgage applications rejected because of it. The House of Commons Library published a briefing this week that confirms what surveyors and lenders have been whispering for years: spray foam can make your home unsellable. That is not hyperbole. It is a direct consequence of how the foam behaves in a roof void.
As reported by the House of Commons Library, the issue is not the foam itself but how it is installed. Open-cell spray foam can trap moisture against roof timbers, leading to dry rot and structural decay within five years. Closed-cell foam, while less permeable, adds significant weight to roof structures that were never designed for it. Either way, a mortgage surveyor now flags it as a material defect, and the lender walks away.
Who qualifies, and who doesn’t
The catch is that spray foam was heavily promoted under the Green Homes Grant and other government schemes. Thousands of households installed it believing they were improving their EPC rating. In many cases, they did, temporarily. But the EPC assessor does not check for moisture entrapment or structural loading. The mortgage surveyor does. The result is a home that scores a C on paper but cannot be sold on the open market.
Energy Saving Trust figures show that a typical loft insulation upgrade costs between £300 and £600. Spray foam installation runs closer to £1,500 to £2,500 for a 3-bed semi. That premium does not buy better performance, it buys risk. The Building Research Establishment has found that improperly installed spray foam can reduce the lifespan of roof timbers by 40%.
What it costs a typical 3-bed semi
If you already have spray foam and want to sell, the remediation cost is brutal. Removing spray foam from a standard loft runs £2,000 to £4,000, plus replacement of any damaged timbers. Some specialist removal firms report that mortgage lenders now insist on a full structural engineer’s report before they will even consider the property. That report costs £500 to £1,000. The total bill can easily exceed £6,000, more than the value of the energy saved over a decade.
But the problem does not stop at sale time. Spray foam also blocks future eco-upgrades. Solar panels require a roof structure that can bear additional weight. Closed-cell foam adds roughly 5 kg per m², enough to push many roofs over their design load. Heat pump installations often require loft space for pipework and buffer tanks. Spray foam makes that space inaccessible.
What this misses, the real problem is certification
The House of Commons Library briefing is careful not to condemn spray foam outright. It notes that foam installed to PAS 2035 standards, the government’s own retrofit quality framework, should be safe. The problem is that most installations in UK homes predate that standard, or were done by installers who ignored it. Ofgem’s own data shows that only 12% of spray foam installations under the Energy Company Obligation were fully compliant with PAS 2035 as of 2023.
The result is a regulatory gap. The government incentivises insulation. Lenders penalise it. Homeowners are caught in the middle. The Mortgage Lenders Association has called for a national database of approved spray foam installations. That does not exist yet. Until it does, the advice from every major lender is simple: do not install spray foam unless you have written confirmation that it meets PAS 2035, and even then, check with your mortgage provider first.
What to do instead, and by when
If you are planning a loft insulation upgrade, choose mineral wool or sheep’s wool. Both cost less than spray foam, carry no mortgage risk, and can be removed easily if needed. If you already have spray foam and are planning to sell, get a structural engineer’s report before listing. The report will cost around £600 but will save you from a collapsed sale six months later.
Households on standard variable tariffs can apply for the Great British Insulation Scheme through gov.uk from 4 November. Eligibility closes on 31 March 2027. The scheme covers mineral wool loft insulation at no cost for low-income households. That is the safe route. Spray foam is not.
Frequently Asked Questions
It depends on whether the foam was installed to PAS 2035 standards and has a certificate of compliance. Most lenders will require a structural engineer's report before approving a mortgage. Without that, many lenders will refuse outright.
Yes, but it is expensive and must be done by a specialist contractor. Removal costs typically range from £2,000 to £4,000 for a standard loft, and you may need to replace damaged roof timbers as well.
