Is spray foam a fire risk?

Current UK product approvals record Euroclass E under BS EN 13501-1 for both open-cell and closed-cell spray foam^[3][4]. RICS's consumer guide describes polyurethane spray foam as combustible, with a reaction-to-fire class of E^[1].

Older approvals used a different test. BBA 10/4771 and BBA 11/4816 give a Class 1 surface spread-of-flame rating under BS 476-7 and no Euroclass, so their results cannot be compared directly with Class E^[6][7]. One of those older documents states that the foam is combustible and requires cavity barriers^[8].

It describes how the foam reacts to a small flame in a standard test: the Euroclass E recorded in current approvals comes from the small-flame test only^[3]. It comes from a small-flame test on the material, not a fire test of a whole roof^[3].

A different class can describe a different system. The manufacturers' association guide says closed-cell foam is class E but can reach class B with an intumescent (fire-protective) coating, and open-cell foam is usually E or F^[9]. If you see a better fire class quoted for a foam product, check what it was tested with.

The government's fire researchers add that exposed foam is likely to perform poorly on fire growth and heat release^[2]. That is why the lining over the foam matters.

In rooms people use, yes, under the approvals checked for this guide. BBA 23/7062 and its predecessor 20/5846 require a fire-resistant board to BS EN 520 everywhere except non-habitable lofts^[3][5]. Kiwa BAR-19-132 requires 30-minute plasterboard in habitable rooms^[4].

So under those approvals, foam in an ordinary, unused loft can be left exposed, while foam in a loft conversion or room in the roof needs a fire-resistant lining over it^[3]. Your own approval number decides the exact rule; see spray foam product approvals explained.

The researchers found that Approved Document B, the fire-safety guidance under the Building Regulations (glossary), has no guidance controlling the fire class of roof-space surfaces^[2]. OFR, the consultants who did the research, suggested future guidance could require foam to be enclosed behind fire-protective linings; that is OFR's view, not a recommendation from the regulator or government^[2].

They found no fire penetration within 60 minutes through any of three old roof coverings with open-cell foam behind them, but foam behind the slate charred^[2]. The Building Safety Regulator published the work on gov.uk on 22 December 2025; it was carried out by OFR Consultants, with tests at BRE in June and November 2023^[2]. The three specimens, as reported^[2]:

All three used one water-blown open-cell foam of about 10 kg/m³, about 90 mm thick but 30–50 mm in places^[2]. For specimen C, OFR concluded that fire got through the covering, while BRE's letter records that specimen as "did not ignite"^[2]. Temperatures behind slate were roughly two to four times those behind clay, but stayed largely below the ignition range the report cites for foams of this kind^[2].

What the tests did not cover:

• Closed-cell foam, a lining, or a matching roof without foam for comparison^[2].
• The full roof fire test: only the penetration stage was run, so a formal classification was not possible^[2].
• How the added fuel would affect a fire inside the building, which OFR said needed a detailed study outside its scope^[2].

OFR also notes that thick, charring insulation can lengthen the apparent time to penetration while adding fuel to the roof space^[2]. The report (Issue R00) is dated 3 July 2024 and was published on gov.uk on 22 December 2025; it says it relies on interim information from BRE and that a revision is expected, and no revised issue had appeared on gov.uk by 23 October 2026^[2].

They say little that is specific: the researchers found no Approved Document B guidance on the fire class of roof-space surfaces^[2]. OFR found that, subject to the test stages that were not run, very old slate and clay roofs with foam could still reach the highest roof-covering classification in Approved Document B, so these set-ups can satisfy current guidance^[2].

OFR still describes retrofit foam as combustible and a long-lasting extra fuel load against the roof covering, which OFR says raises the likelihood of fire spreading across a boundary if the covering is penetrated^[2]. It treats whether spraying foam into an existing roof counts as "building work" as an open question: if it does, the added fuel could make a fire inside the building more severe^[2]. The regulator was considering broader future work as of 19 October 2026^[2].

OFR also concluded that suppliers often apply retrofit foam on the owner's instruction without considering Building Regulations compliance^[2]. Trading Standards guidance for installers (November 2025) lists Approved Document B alongside Approved Documents C, F and L^[10]. The BBA warns that the regulatory statements inside product approvals may be out of date, because fire, energy and ventilation rules changed several times in 2022^[11].

Product approvals set conditions for these, and they do not all agree^[3][4]. The industry Code of Practice sets no requirements for cables, downlights, flues or fire linings, so the conditions come from the approval for your product^[12].

• Cables: BBA 23/7062 requires cables in conduit or trunking^[3]. BBA 20/5846 forbids spraying over cables not in conduit or trunking, asks for de-rating to be considered, and requires a check afterwards that cables are unobstructed^[5].
• Why cables matter: under the wiring regulations, a cable totally surrounded by thermal insulation for more than 0.5 m has its current-carrying capacity halved^[13].
• Recessed downlights: BBA 23/7062 requires recessed lights to be protected, and Kiwa BAR-19-132 requires 75 mm clearance^[3][4]. BBA 10/4771 bans recessed lighting outright, so the documents disagree^[6].
• Flues and chimneys: BBA 23/7062 says flues must not be sprayed, and Kiwa BAR-19-132 requires flues to be isolated with non-combustible insulation^[3][4].

The PCA and RPSA's Sprayed Foam Insulation Inspection Protocol (March 2023), used by trained surveyors, has no fire section^[14]. For the full list of installation conditions, see how spray foam should be installed.

Research on polyurethane foams in general describes the gases they produce when they burn; it is not a test of loft spray foam in UK homes^[15]. A peer-reviewed 2016 paper by McKenna and Hull found burning polyurethane foam produces significant carbon monoxide and hydrogen cyanide, plus nitrogen oxides and isocyanates^[15].

On that paper's measures, rigid foams were slightly worse than flexible ones, PIR foam the worst, and hydrogen cyanide yields rose as ventilation fell^[15]. For fumes from spray foam during installation and afterwards, see spray foam fumes and health.

RICS advises checking with your buildings insurer, because the foam is combustible^[1]. No published insurer wording or ABI statement on spray foam was found in the research for this guide (October 2026), so it is not known how insurers treat it in general. If you contact your insurer, keep a copy of what you told them and their reply.