The short answer
Spray foam is combustible, so it is a fire risk in the way any plastic insulation is. Some products are treated with fire retardant and are tested to a reaction-to-fire class, but they still burn when exposed to enough heat and can give off dense smoke and toxic fumes. The danger is greatest where foam is applied close to chimneys, flues, recessed lights or cables, so those details need checking.
How spray foam behaves in a fire
Spray foam is made from polyurethane, a plastic produced by mixing two liquids that react and expand. Cured, it is a solid foam full of tiny cells, and like most organic insulations it will ignite if heat and oxygen are present for long enough. Products differ. Some are formulated with flame retardants and have a published reaction-to-fire classification, and an installer should be able to show you the data sheet for the one used. A classification describes behaviour in a controlled test and does not mean the foam is fireproof.
What makes foam fires worrying is smoke. Burning polyurethane produces dense black smoke and gases that are harmful to breathe, and in a loft directly above bedrooms that is a real concern. The foam can also continue to burn after the source of ignition has gone, and it is hard to extinguish once it has taken hold inside a roof structure. It is the product, not just the flames, that firefighters worry about.
Where the risk is concentrated
The greatest risk is not the open roof slope but the points where heat or electricity are present. Chimney stacks and flues get hot, and foam sprayed hard against a flue or brickwork can be heated for years. Building standards require combustible insulation to be kept clear of heat sources by set distances, which is why a competent installer cuts back and leaves a gap at the stack. A stack buried in foam is a warning sign.
Wiring is the other concern. Cables buried in foam cannot shed heat as they do in free air, and electricians have a rating adjustment for cables in thermal insulation. Recessed downlights that poke up into a loft can overheat if foam surrounds them, unless they are rated for covering. And loft lights, extractor ducts and junction boxes all deserve a check. If you have had foam fitted and an electrician has not inspected the circuits, it is worth arranging.
What to check in your own loft
From the hatch, with a torch, look at the chimney breast and any flue pipes: is there a clear gap between them and the foam, or is the foam right up against the masonry? Check whether any downlights or cables are buried. Look for scorching, discolouration or a burnt smell near the stack. Do not cut into the foam to look. If you cannot tell, a survey can. We are roofers, not electricians or fire engineers, so where we see a concern we photograph it and tell you to ask a qualified person to assess it.
Keep paperwork for the product too. The data sheet should show the manufacturer, the product name and its fire classification, and the invoice should show the thickness. Our page on spray foam paperwork lists what to keep.
Building control and the wider picture
Fire safety forms part of the Building Regulations, and the way foam is applied in a loft conversion, which has people sleeping above and means of escape to protect, is judged more strictly. Our page on spray foam and building regulations sets out where it fits. If you are concerned about a particular installation, the building control body you use, whether the council or a private approver, can advise on what applies.
It helps to put the risk in proportion. Most loft fires start from an electrical fault, a flue or a heat source close to something combustible, not from the foam itself, and foam sprayed neatly with proper clearances is a smaller worry than foam sprayed carelessly round a chimney. That is why the questions to ask are about detail: how close is the foam to the flue, are the cables derated, and is there any heat source in the roof space. A general worry about the product tells you less than looking at your loft.
Smoke alarms count as well. Many lofts conversions and attics lack a detector above the stairs or on the landing, and where there is combustible insulation overhead, a working alarm gives time to act. Test them as a matter of routine.
What removal changes
If the foam is against a flue or has covered wiring, removal in that area makes sense whatever its condition elsewhere. Partial work is possible and we cover it in partial spray foam removal. The foam around a chimney is cut back to leave the required clearance, and the gap is filled with a non-combustible material where needed. The rest can stay if the roof is dry and sound.
We do the roof side of this, with photographs, so you have a record. Our spray foam page sets out the full service, and the quote is fixed once we have seen the loft.
Every roof is different. A free survey with photos settles it for yours.
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