Spray Foam Insulation: Costs, Risks & Mortgage Issues

Spray polyurethane foam (SPF) insulation was heavily marketed in the UK, often through cold calls or unsolicited offers.¹ The pitch was compelling: a contractor sprays foam directly onto roof timbers or between joists, it expands and sets, and the loft becomes thermally sealed in a single visit.

The reality has proved far more complicated. By the mid-2020s, spray foam has become one of the most contentious issues in UK residential property, not primarily because of how it performs thermally, but because of what it does to a property’s mortgageability and saleability. If you are considering having spray foam installed, or you’ve bought a property where it already exists, read this guide before making any decisions.

How Spray Foam Insulation Works

There are two distinct types of spray foam:

Open-cell spray foam (OCF) expands a great deal as it is sprayed and sets into a soft, spongy material. It is vapour-permeable and relatively easy to remove, but it provides less structural rigidity and lower thermal performance per millimetre.

Closed-cell spray foam (CCF) expands less and sets into a rigid, hard material with high compressive strength. It is far more resistant to water vapour, gives better thermal performance per millimetre, and bonds very strongly to whatever it contacts. In modelling for the Building Safety Regulator, closed-cell foam was given a thermal conductivity of 0.026 W/mK against 0.039 W/mK for open-cell, and a vapour resistance factor of about 61 against 3.3.²

The fundamental problem for UK housing is that many domestic installations sprayed foam, open-cell or closed-cell, directly onto the underside of the roof: the rafters, the underlay or sarking boards, and sometimes the tiles themselves.² This:

1. Makes it difficult or impossible to inspect the timber beneath without disturbing the foam¹
2. Can trap moisture and hide a roof leak, potentially causing concealed rot¹
3. Can mask pre-existing structural defects
4. Cannot be removed without significant effort, cost, and risk of timber damage

Mortgage Lender Positions

This is the central issue for most homeowners. Many mainstream UK mortgage lenders will not lend on properties where spray foam has been applied to the roof structure, or will lend only once a specialist inspection report shows the timbers are sound. Research by the HomeOwners Alliance with the BBC found that only 25% of mortgage lenders, and no equity release providers, would lend where spray foam had been installed as a retrofit.³ Positions vary between lenders and change over time, so check with the lender directly before a valuation.¹

The lenders’ main concerns are that a surveyor cannot see the condition of the timbers beneath the foam, and that some installations can trap moisture.³ A standard RICS homebuyer survey or mortgage valuation cannot confirm whether the hidden timbers are sound, rot-free, and correctly notched and fixed. From the lender’s perspective, they cannot adequately assess the security for the loan.

The practical consequence: a property with spray foam in the roof can be hard to sell to buyers who need a mortgage, and sellers often face either removing the foam or discounting the price to reflect the smaller pool of buyers.

Cost of Spray Foam Installation

Despite the risks, if you are committed to spray foam (perhaps in a non-residential building, a garage, or a property you own outright), here are realistic 2026 costs:

For a standard 3-bed semi-detached with a 55 m² loft floor, the sloping roof area to be sprayed is roughly 70 m², so at the rates above installation typically runs about £1,050–£1,750 for open-cell or £1,400–£2,450 for closed-cell. Some contractors offer loft-clearing and preparation as an extra.

Spray Foam Removal Costs

Removal is significantly more expensive than installation, and the result is often not a timber in the same condition as before. Closed-cell foam bonds chemically to timber and cannot be simply peeled off, it must be mechanically chipped and scraped, a process that is labour-intensive and often damages the timber surface. A structural survey afterwards is advisable to confirm the condition of the timber.

The HomeOwners Alliance warns that removal is likely to cost thousands of pounds, more than the original installation, and that the whole roof may need replacing.⁴

After removal, a structural engineer or RICS surveyor should inspect the timbers and provide a report confirming their condition. This report, with confirmation of the removal, is typically what lenders and their valuers will want to see before reinstating a mortgage offer.

Removal is not always straightforward

Some foam installers applied foam over fragile or already-damaged sarking felt or boards. Removal in these cases can cause the existing underfelt to tear, requiring reroofing in addition to foam removal. Get a specialist assessment before instructing removal.

The RICS and Government Position

RICS (Royal Institution of Chartered Surveyors) publishes a consumer guide on spray foam insulation. It says a surveyor who finds spray foam during an inspection may request an independent specialist report, the results of which could affect their opinion of value.¹ RICS does not prohibit spray foam, but it stresses that a timber roof structure covered with foam cannot be fully seen or inspected, and that concern underlies much of the lenders’ caution.¹

Government grant schemes have funded spray foam: the Energy Company Obligation (ECO4) funds its installation for eligible households, and the Great British Insulation Scheme (GBIS) did the same until it closed on 31 March 2026.⁵³ ECO4 itself has been extended to 31 December 2026.⁵ Research published by the Building Safety Regulator in March 2024 found the moisture risk to roof timbers was low when open-cell foam was applied in line with the guidance in BS 5250:2021, that an air and vapour control layer reduced the risk where foam met a high-resistance underlay, and that the highest risk came from spraying foam directly onto the roof covering.⁶ The House of Commons Library notes the government’s position that spray foam installed in line with the relevant standards should not need removing or stop a homeowner getting a mortgage.⁷

The Insulation Manufacturers Association (IMA) published a code of practice for installing spray foam in domestic roofs in May 2023, which says only installers trained and approved by the product’s manufacturer should apply it.⁸ Installation standards in the market have historically been inconsistent.

When Spray Foam Might Be Appropriate

There are legitimate uses for spray foam in residential and commercial contexts where the mortgage-ability concern doesn’t apply:

• Outbuildings, garages, and workshops, not mortgaged, so lender concerns irrelevant; closed-cell foam works well on concrete block walls and metal roofs
• Van, bus, and motorhome conversions, spray foam is commonly used for complex geometries
• Commercial and industrial roofing, applied to the top of flat roof decks under single-ply membranes, this is an established technique
• Below ground structures, spray foam on basement walls or retaining structures where standard board insulation is impractical
• Properties owned outright without mortgage, owner bears the risk; needs to be disclosed on sale

Even in these cases, confirm that no mortgage will ever be needed on the property before committing. Properties change hands, and a buyer’s lender, not the current owner, determines whether spray foam is acceptable at point of sale.

If You Already Have Spray Foam

Before selling: Disclose the presence of spray foam through your property information form (TA6) and your solicitor, and pass on the installation paperwork. Buyers can rely on the TA6 answers, and if you give misleading information the buyer may be able to claim compensation after completion.⁹ Consider commissioning a specialist report proactively, this demonstrates due diligence and may reduce the price discount expected by a cash buyer. The HomeOwners Alliance puts a specialist surveyor’s inspection of the roof and paperwork at around £500–£700.⁴

Before remortgaging: Contact your existing lender before instructing a valuation. If they are unwilling to remortgage without removal, you need to factor removal costs into your plans before instructing a surveyor (and paying their fee).

If you want to stay: If you have no plans to sell or remortgage, the thermal performance should continue for the life of the foam. The risk is the concealed moisture trap, if your roof covering is in good condition and there is no existing moisture ingress, the risk is reduced but not eliminated. Consider having a roofer inspect the external covering carefully and annually.

Key Questions to Ask Before Installing

1. Will this affect my ability to sell or remortgage?
2. Can the installer provide evidence of BBA, Kiwa or equivalent third-party certification for the specific foam product?
3. Is the installer trained and approved by the foam’s manufacturer, and working to the IMA code of practice?
4. Will a structural survey of the timbers be provided before foam is applied?
5. What is the installer’s warranty, and is the company likely to still exist to honour it?

On the second question: UKAS suspended all of the BBA’s accreditation on 26 February 2026, and while that stands the BBA cannot issue new certificates under UKAS accreditation.¹⁰ UKAS says existing accredited certificates remain valid until their expiry date.¹⁰ Trading Standards guidance asks for the product to hold an independent test certificate from a recognised body, such as the BBA or Kiwa.¹¹

If you cannot get satisfactory answers to all five, do not proceed with spray foam installation on a residential property.