The short answer
A smell in a foamed loft usually points to one of three things: the foam itself giving off a chemical odour, damp or mould in the rafters and boards it covers, or an unrelated source such as a blocked flue or a dead animal in the eaves. Smell alone cannot say which. An inspection of the foam, the timbers and the ventilation is what separates a harmless odour from a moisture problem.
What a smell from spray foam can mean
Spray foam is a plastic made on site by mixing two liquids that expand and set against the underside of the roof. When the mix goes on well, it cures and the odour fades within a short time. When something goes wrong, the odour can hang around for months, and a lingering smell is often the first thing a homeowner notices.
There are broadly three explanations. The first is the foam: a sharp, chemical or fishy smell can come from foam that did not cure properly, for example because the two liquids were not mixed in the right proportions or the roof was too cold or damp when it was sprayed. The second is moisture: a musty, earthy smell suggests damp, and damp in a foamed roof is a different problem from the foam itself. The third is neither. Loft smells also come from dead birds or rodents, old stored items, a leaking soil pipe or a blocked flue.
Working out which one you have matters, because the fixes are very different. Nobody should guess from the doorway of the loft hatch, and nobody should rip out foam on the strength of a smell alone. Our main spray foam insulation removal page sets out how the whole process runs, from survey to re-insulation.
A chemical smell versus a musty one
Describe the smell carefully, because the description helps. A sharp, plastic or fishy odour that is strongest near the foam and was noticeable soon after installation points towards the foam. A smell that is stale, earthy or like a damp cellar points towards moisture and possibly mould.
The musty kind deserves more attention. The RICS consumer guide cautions that insulation installed badly can bring dampness, uncontrolled condensation among it. The Energy Saving Trust makes a related point in its loft advice: a leaking or condensing roof puts the structural timbers at risk of decay. Foam hides the wood it is stuck to, so by the time a smell reaches the living space, the damp may have been at work for a while.
Pay attention to timing as well. If the smell gets stronger after rain, a leak is a likely suspect. If it is worst on cold mornings or when the heating is on, think condensation. Our guide to spray foam and roof condensation explains how that moisture forms and why it collects where you cannot see it.
What we look at on site
A survey starts with the obvious things before it gets technical. We look at the foam surface for shrinkage, cracking, gaps beside the rafters, a sticky or powdery feel and any change of colour. We look for staining on the ceilings below, on the gable walls and around the eaves. Where the foam stops short of the timber or the wood is exposed at an edge, we check what it looks and feels like: dark, soft, flaking or crumbling wood tells its own story.
Then we look at everything that is not the foam. Blocked or disconnected flues, broken vent pipes, a gap in the soffit that lets birds in and any sign of nesting all produce smells that people blame on insulation. If we spot bat droppings or an active nest, work halts at once, because bats and nesting birds are protected and have to be handled correctly.
Pictures from your own loft and roof slopes go with the written quote, which lets you judge the evidence yourself. If there is a leak, the covering outside gets the same close look as the foam inside.
Does a smell mean the foam must come out?
Not automatically. If the odour comes from something else, the foam stays and the real cause is fixed. Where the foam looks intact and the timber behind it is dry, a faint smell that fades over time may simply be left alone. Our page on whether spray foam has to be removed covers how that decision is made.
Removal becomes a serious option when the smell goes with evidence of trapped moisture, soft or darkened rafters, or foam that is visibly failing. Our advice favours doing only as much as the fault demands. Sometimes that means opening up one section to inspect the timbers before anyone commits to stripping the whole roof.
If the foam does need to go, it is cut and scraped back by hand, the exposed roof is inspected, and new insulation goes in to suit the building. Timings depend on roof size and how stubborn the foam is, and our page on how long spray foam removal takes explains the stages.
Costs, rented homes and what to do now
In its August 2026 update, MyBuilder's cost guide gives a national range for removal of £20 to £50 per square metre, averaging around £1,500, with an assessment typically £100 to £200. Those are typical UK figures, so treat them as a rough frame of reference. The roof area, the type of foam, how firmly it has stuck to the wood and how high the scaffold must go all shift the total. A firm figure only comes once we have been up there and looked.
If you rent, tell your landlord in writing and note the date you first noticed the smell. Responsibility for a foamed roof usually sits with the owner, and our page on spray foam in a rented property sets out the points to raise.
In the meantime, open windows in the rooms below, leave the foam undisturbed and keep absorbent items out of the loft. If the smell is strong or makes you feel unwell, stay out of that space and arrange an inspection. Ring 01793 626096, drop us a WhatsApp, or send the enquiry form. Workmanship carries a 10-year guarantee, given in writing.