Spray Foam Insulation: Risks, Mortgages and Removal

Spray foam insulation is a polyurethane foam applied with a spray gun to the inside of roofs, into walls and under floors, where it expands and sets to form a continuous insulating layer¹. In UK homes it is most often sprayed onto the underside of a sloping roof in a loft, and it is also used under suspended timber floors³. An estimated 250,000 UK homes have had it installed⁴.

For a three bedroom semi-detached house, the National Insulation Association gives a typical cost of around £2,500 for professionally installed spray foam loft insulation, with a guide price of around £20 to £50 per square metre: the lower figure for a thin stabilisation layer, the higher for a thicker insulating layer⁵. Removal is costed at about £40 per square metre⁶, and official 2025 figures put removal of spray foam and cavity wall insulation from a typical three bedroom semi at between £2,000 and £3,200⁷.

The problems are well documented. Government modelling of foam applied to timber sloped roofs found the highest risk where foam is applied directly onto the roof covering, with high risk under all modelled scenarios in that case⁸. Citizens Advice reports that 1 in 3 people with spray foam insulation in their loft have experienced problems⁹. The government position is that where foam has been installed in line with the relevant standards it should not require removal or prevent a homeowner obtaining a mortgage⁶, but in practice lenders have been cautious and households have run into difficulty when selling¹⁰.

What spray foam is and where it goes

Spray foam is applied wet using a spray gun, then sets in place to form an insulating layer¹². Installers mix the product on site at the property¹³. Both open cell and closed cell types are usually made from polyurethane and filled with bubbles of gas or air⁵. In retrofit jargon, PU foam means polyurethane foam, a closed cell insulation that can be sprayed¹⁴.

Three applications dominate in UK housing:

• Pitched roof slopes. Where a home has a pitched roof with an uninsulated loft, foam is sprayed onto the underside of the sloping roof as an alternative to mineral wool at joist level¹². Retrofitted spray applied closed and open cell polymeric insulation to the underside of roofs of dwelling properties is the configuration that official fire testing examined¹⁵.
• Walls. Foam is sometimes sprayed into empty cavity walls, usually where standard cavity wall insulation is not considered suitable¹².
• Suspended timber floors. Foam is sprayed to the underside of the floor, often using a robot to access the underfloor space¹². Q-Bot's robotic spray foam installation is priced from £3,250 for a floor up to 25m², then £126.50 per additional square metre¹⁶; Which? reports costs starting at around £3,000 to £4,500 for a typically sized two or three bedroom terrace¹⁷.

Underfloor spray foam is not the same proposition as loft spray foam. Some loft installations leave roof timbers on the cold side of the insulation, allowing condensation, damp and damage where ventilation is poor or blocked¹⁸. The appeal of the material is that it reaches hard places: the nozzle gets into small gaps and the foam expands to fill the space. That is also why it is hard to undo.

Open cell or closed cell: the two types compared

Spray foam comes in two forms, and the difference matters more for moisture than for warmth⁶.

Open cell foam is often used as sound insulation because it blocks and reduces airflow⁵. Closed cell foam acts as a vapour barrier that can reduce ventilation⁶, and its rigid nature creates a barrier that traps air and moisture, which can lead to condensation and decay in timber framed roofs¹⁹.

Neither type is inherently safe or unsafe. Official modelling found high risk in London where open cell insulation is applied with no air and vapour control layer present, reducing to low risk when a closed cell insulant and/or an air and vapour control layer is used⁸. The same modelling found high levels of risk in Newcastle without that layer, reduced to medium or low by its presence⁸. Performance therefore depends on the whole build-up, not the choice of foam alone. As a rough measure of thickness, 100mm of spray foam is equivalent to around 170mm of mineral wool loft insulation⁵.

What it costs, and how that compares

The headline figure from the National Insulation Association is around £2,500 for professionally installed spray foam loft insulation in a three bedroom semi-detached property, within a guide range of £20 to £50 per square metre⁵. Which? reporting in February 2024 gave a typical cost of between £600 and £1,100, and recorded a Care and Repair Cymru older client who paid £3,500 for spray foam loft insulation²⁰. Those figures are not reconcilable into a single number: the spread reflects roof size, the thickness applied and, in mis-selling cases, what the householder was persuaded to pay. Spray foam is much more expensive to install than standard mineral wool laid on the loft floor³, and mineral wool may be cheaper and better at insulating¹.

Removal is the cost that catches people out. Guide figures are about £40 per square metre⁶, with the Centre for Sustainable Energy describing removal as very expensive, in the thousands of pounds for most properties³. Official 2025 analysis puts removal of spray foam and cavity wall insulation at between £2,000 and £3,200 for a typical three bedroom semi, against around £700 for removing rockwool or fibreglass loft insulation⁷.

The risks: condensation, timber decay and hidden defects

The Building Safety Regulator published modelling on 28 March 2024 investigating the level of moisture and timber degradation risk where a sprayed foam insulant is applied to typical domestic timber roofs; the publication applies to England⁸. Its central findings were that the highest risk assessed is when spray foam is applied directly onto the roof covering, leading to high risks under all modelled scenarios, and that higher levels of risk arise in some scenarios when foam is applied to high resistance underlay⁸. A related exchange of letters on spray foam insulation was published in May 2024²¹.

Independent advice points the same way. The Centre for Sustainable Energy cites a Health and Safety Executive study suggesting spray foam causes timber decay in more than a quarter of all cases when applied directly to the underside of roof tiles³. The Energy Saving Trust explains the mechanism: spraying foam directly to the underside of the roof partially seals the timber, so leaked rainwater can cause rot and condensation can cause similar problems, with lower risk from open cell foam¹². Where a closed cell layer is used, ventilation of the room or loft has to be maintained to avoid a build-up of condensation⁵.

Three practical consequences follow for the household:

1. Defects get hidden. Foam can cover up roof problems¹, and a layer of spray foam makes a survey of the roof impossible, which may mean solar panels cannot be installed later³.
2. The roof has to be sound first. No insulation system should be applied to a leaking roof; the roof must be fixed first¹², and missing or slipped tiles must be fixed before applying foam²².
3. Loft conversions are a poor fit. Foam is not recommended in loft conversions because it carries a higher risk of damaging the roof structure²³.

There are safety points beyond moisture. Harmful fumes are produced during installation and in the days the material takes to set, and if poorly installed dangerous chemicals can continue to leach out for a long time afterwards³. Foam can be harmful to handle, particularly if it is not cured properly²⁴. Some types can cause damp problems or be a fire risk if not properly installed, or where cheaper products are used²⁵. On fire performance specifically, official testing concluded that such sprayed configurations can satisfy the highest demands for roof covering classification as currently included in Approved Document B guidance¹⁵. Related issues are covered under insulation safety and fire and condensation, damp and mould after insulation.

Spray foam and mortgages: why lenders ask questions

The official line is now reasonably clear. Where spray foam insulation has been installed in line with the relevant standards, it should not require removal or prevent homeowners obtaining a mortgage⁶. In a Commons debate on 17 June 2026 a range of major lenders, including Nationwide, Lloyds, Santander and Barclays, were reported to have confirmed that they will not take a blanket approach to houses with spray foam¹⁰.

That is a change of tone rather than a clean slate. The Federation of Master Builders states that mortgage lenders are wary of spray foam insulation and often refuse to lend to buyers where it has been installed²⁶. RICS noted in 2023 that concern within specific sectors of the lending market, such as equity release mortgages, was by then having a wider impact on lenders²⁷. Citizens Advice found that some affected homeowners are unable to sell or remortgage as lenders become increasingly wary⁹, and the same debate acknowledged that many households who had spray foam installed have encountered problems when selling their home¹⁰.

The underlying reason is assessment, not ideology: lenders and valuers have struggled with the difficulty of assessing the structural integrity of insulated lofts¹⁹, which is a direct consequence of foam making the roof unsurveyable³. The Energy Saving Trust judges that mortgage issues were possibly true for a while, but that industry progress in determining whether a house is at risk means there should be less of an issue where foam was installed correctly¹². The Insulation Manufacturers Association published a code of practice for the installation of spray foam insulation in roofs in May 2023⁶, which is part of that industry framework.

Selling a home with spray foam: what paperwork carries weight

The presence of spray foam can make homes harder to sell, particularly if a survey finds the insulation was poorly installed³. The defence is documentation. Citizens Advice sets out four items a household should hold²:

• a report from a survey carried out before any work started
• a product certificate showing what type of spray foam was used
• a guarantee from the trader who carried out the work
• a guarantee from the manufacturer of the insulation

A proper pre-installation survey should include a U-value calculation showing how well insulated the home is, an assessment of the risk of condensation occurring, and identification of any problems and the measures needed to prevent them⁵. RICS has observed that this form of insulation, widely used for several decades, can all too often be marketed as an easy fix when it is a significant alteration needing careful consideration²⁷. Where removal is being pressed by a buyer or a valuer, the sensible order is assessment first: check with a building surveyor before paying to have spray foam removed, or use a specialist spray foam assessor from the Property Care Association¹. More detail sits on the spray foam paperwork page.

Removal is difficult, costly and sometimes effectively permanent

Spray foam is considered a permanent installation, and removing it at a later stage might also require replacing the structure it was applied to¹². Once applied it can be a very difficult and costly job to remove²⁸. Timbers coated in foam are more difficult to replace, as are tiles or slates where there is no roofing felt or other layer between foam and tiles¹². Under floors, foam is difficult to remove from joists, wires and pipework, so it presents a problem when maintenance work is needed in that area in future²⁹.

The reasons householders seek removal are damp and condensation, damage to the property, or the need to make a repair such as a roof repair¹. Removal is not automatic: the government position that compliant installations should not require removal⁶ means the assessment step matters financially as well as technically.

Where spray foam does not belong

Spray foam should not be used in listed buildings or houses with thatched roofs⁵. Listed building consent must be obtained before installing it anywhere in a listed property, and consent is unlikely to be granted³. Older homes generally are a poor fit: spray foam can be effective but is not suitable for all homes, especially older ones, and independent advice should be taken before considering it³⁰. See insulating and glazing a listed building and retrofitting traditional and pre-1919 buildings.

There are narrower cases where foam is proposed on merit: some types are waterproof but also breathable, which has been described as suiting homes in flood-prone areas⁵, and foam may occasionally be more suited to a property than polystyrene beads in a cavity wall, where the installer should advise¹². The Centre for Sustainable Energy's November 2025 review concluded that in almost all cases installing spray foam carries considerable risks and other forms of insulation should be considered first³. Which? notes that there are controversies around spray foam and that badly installed foam can be very damaging to a home²². Alternatives are compared on the insulation materials page and in spray foam vs mineral wool for lofts.

Installation, certification and avoiding mis-selling

Spray foam should always be installed by a professional, installers must be trained and assessed by the BBA, and the product should have a BBA certificate or equivalent⁵. The BBA's own position is that installation of such materials is a technically complicated area requiring the use of suitably experienced construction professionals³¹. Spray foam can only be installed by a professional who mixes the product at the property¹³, and the installation must conform with the manufacturer's requirements, building regulations, and health and safety rules²⁰.

Although spray foams are mainly professionally installed, they are also available as a DIY measure²². Because of the safety issues, the National Insulation Association strongly warns against DIY spray foam installation⁵.

Before any work, independent advice from a buildings surveyor is advised, or at least three quotes from different home improvement traders if surveyor advice costs too much¹. The Energy Saving Trust suggests getting multiple quotes from accredited installers such as TrustMark-registered companies, looking for genuine customer reviews, and keeping the property well maintained¹². Related guidance sits on finding an insulation installer and insulation scams and cold calling.

What it means for energy independence

Insulation is the one measure that reduces a household's demand for bought energy permanently, without a supplier, a tariff or an app. Spray foam delivers that in physical terms, and 100mm of it is equivalent to around 170mm of mineral wool⁵. What it can also do is transfer dependence elsewhere: onto a manufacturer's guarantee and a trader's guarantee², onto a lender's willingness to look past a valuer's caveat⁵, onto a specialist assessor if damp appears¹, and onto a removal contractor charging around £40 per square metre if the roof has to be opened up⁶. A material that cannot be surveyed through also forecloses options, including solar panels³.

The evidence base is mixed rather than uniformly negative. Official modelling identifies specific configurations that are high risk and specific ones that are low risk⁸, and the government maintains that compliant installations should not trigger removal or block a mortgage⁶. The practical question for a household is whether its own roof, its ventilation and its paperwork can be shown to sit on the low risk side of that line.