Should you seal an asbestos roof?

1A coating changes the surface, not the material

Asbestos cement is cement reinforced with asbestos fibres, and the corrugated sheets on many older garages and outbuildings are exactly that. Where a building dates from before 2000, HSE's advice is to assume asbestos is present. Sealing, sometimes called encapsulation, means brushing or spraying a coating over the weathered surface so the sheets are protected from further weathering and look tidier.

What a coating does not do is take anything away or make the sheets stronger. The cement underneath is the same age, with the same brittleness, as it was the day before the brush went on. So the real decision has little to do with paint. It is whether leaving this material in place is a sensible choice for your particular garage, given what the building is used for, who goes near it and how many more years you expect to keep it.

A sound, dry garage that holds a lawnmower and some boxes is a very different case from a workshop that is used daily or a roof that overhangs a path.

2Sheets that suit sealing and sheets that do not

Condition decides almost everything. HSE treats cement sheeting that has simply weathered, and is otherwise intact, as non-licensed work, and that is the kind of roof where a coating is worth discussing: whole sheets, no holes, no crumbling edges, fixings still sound and no sign of the corrugations flattening.

Cracked, holed or flaking sheets are a different matter. A coating cannot bridge a broken sheet, and anyone working up there is standing on a material that HSE describes as always fragile. We start with a torch from inside the garage, looking up, because the underside shows cracks, earlier patches and tired purlins that the weathered top surface hides. If the timbers carrying the sheets are failing, coating the sheets solves nothing, and the plain advice may be to plan for overlay or removal instead. Moss and lichen on the surface are not a defect in themselves, but heavy growth can mask cracks.

3Preparation is where the risk sits

Before any coating will grip, a weathered cement surface has to be cleaned, and cleaning is the step that disturbs it. Anything that scrapes, grinds or blasts moss and old paint off the sheets can lift fibres and fragments that were safely bound into the cement. So ask any contractor to describe the preparation step by step, and put dry brushing, scraping and power washing to them as direct questions rather than assuming the answer.

HSE draws a line where sheets begin crumbling and giving off dust in quantity: from there the job is notifiable non-licensed work, with a notice needed before it starts. That line is a useful test for any proposed method. A plan that risks crumbling the sheets has already stopped being a sealing job and moved into a stricter category. We tell you plainly if the sheets look too far gone to prepare at all, and we would rather say that than coat over a problem.

4Setting a coating against overlay and removal

HSE's own guidance on cement roofs asks whether sheets can be covered over with a non-asbestos material, rather than taken off, and that route deserves pricing beside a coating. Our page on overcladding asbestos sheets explains how it works and what the structure must carry.

On cost, MyBuilder (updated 21/08/2026) puts taking off a single garage roof at £350 to £1,295 and a double garage at £650 to £1,800, as typical UK ranges. A coating buys time but ends nothing, and most coatings need renewing sooner or later, which brings more preparation each time. Removal closes the question once. The quote we write after the survey gives one total price, backed by photographs of the roof itself, so the comparison is made on your garage and not on a national average.

5Conversions, carports and your insurer

If the garage is turning into a living space, a coated asbestos roof is awkward to insulate and line from below, because every fixing and board disturbs it. What the roof needs in a garage conversion sets out the order of work. Carport sheets of the same age raise the same questions, and our carport roof replacement page covers the open-sided case.

Your buildings insurer may also have a view on an asbestos roof, so check the policy wording and put the question to them before any money is spent; garage roof insurance goes through the usual points. If your garage has a flat roof covered in felt instead of cement sheets, none of this applies, and garage felt roofs is the page to read. The wider picture sits on our garage roof replacement page.