The short answer
You cannot confirm asbestos cement by eye. Grey, corrugated, brittle-looking sheets on an older garage are a warning sign, but only a laboratory analysis of a small sample gives a firm answer. Until you have one, leave the sheets whole: do not drill, scrub, sand or break them, and book a survey before any repair or replacement.
What asbestos cement sheets look like
Cement sheet made with asbestos fibres is pressed flat or into waves, and the wavy kind is what roofs usually carry. On garages it is most often the large corrugated sheet, lapped along its length and bolted down through the high point of each wave. The surface is usually a dull, chalky grey, and over the years it picks up a patchwork of green and black growth, orange lichen and pale streaks where water has run.
Look at the edges and the fixings. Old sheets tend to be thick at the cut edge, with a layered, fibrous look. The bolts or screws often carry a bitumen or plastic cap, and the ridge may be a separate cement fitting rather than a folded metal one. Modern fibre-cement sheets and some profiled metal sheets can look very similar from the driveway, which is exactly why appearance alone proves nothing.
An age clue helps but does not settle it. A garage that came with the house, with a rough, weathered grey roof and no insulation or lining, is more likely to carry old cement sheet than a recently built outbuilding. Even so, an old roof may already have had one new covering, which means the sheets above you could be younger than the walls beneath them.
Why a test is the only real answer
Asbestos fibres are far too fine to see. Two sheets that look identical can be completely different materials, and the label on the back of a sheet, where there is one, may have weathered away or been painted over. The only reliable check is a small sample analysed by a laboratory that tests building materials.
Taking that sample is itself a job to do carefully. The aim is a small piece from an edge or an already broken corner, taken without creating dust, with the area damped first and the piece sealed straight into a bag. If the sheets are intact and in sound condition, many people prefer to have a surveyor do this rather than try it themselves. Paying for a test is a small step beside the cost of getting the next one wrong.
A survey result also tells you what you are dealing with before you ask for prices. Quotes for a garage roof that has been confirmed as cement sheet are easier to compare than quotes written on a guess, because every bidder is pricing the same job.
What not to do while you wait
Whether the sheets turn out to be asbestos or not, treat them as if they might be until the result comes back. HSE guidance on non-licensed work rests on one idea: careful handling without breaking the material up. Intact cement sheet that is left alone is a very different thing from sheet that has been cracked, drilled or scrubbed.
- Do not drill or screw into the sheets. A satellite dish, a light or a shelf bracket fixed through the roof makes holes and dust.
- Do not scrub, brush or pressure wash the moss. Cleaning grinds the surface and sends particles into the air and across the garden.
- Do not walk on the roof. Aged sheets are brittle, and a person's weight can break them and put the walker through the roof.
- Do not sweep up broken pieces. Leave them where they are, keep children and pets away, and mention them when you call for a survey.
If a sheet has already cracked or fallen, say so when you book. Substantial breakage changes how the work is classed under HSE guidance, because it moves from non-licensed work to notifiable non-licensed work. We explain that difference in our page on what asbestos garage roof removal costs.
Other clues around the garage
If you have paperwork from the purchase, the survey or a previous owner may mention the roof covering. A home buyer's report that describes the garage as having a cement sheet roof is a strong lead, though it still needs confirming for the sheets you actually have.
Look inside as well. Many garages have no ceiling, so you can see the underside of the sheets from the floor. Underneath, the cement often looks smooth and grey with a slightly rough texture, and you may see the purlins, the timber or steel members spanning the walls to hold the sheets up. Fine dust or flaking on the floor beneath a weathered roof is worth noting, but do not sweep it. Photograph it from a distance instead.
Neighbours help too. Garages in the same block or on the same estate were often built together, with the same roof covering. If your neighbour had theirs tested or replaced, ask what they were told. It gives you a lead, not a result, but it saves guesswork when you start planning the work.
Next steps once you know
If the test comes back negative, the roof is an ordinary sheet roof and can be repaired or replaced like any other. If it is positive, you have choices. Sound sheets can sometimes be left alone, overlaid or removed, and which is right depends on their condition, the structure beneath them and your plans for the building. Our garage roof replacement service covers the wider job, and our guide to the asbestos garage roof options walks through each route.
For removal, careful lifting of whole sheets is non-licensed work under HSE guidance, provided the sheets come off whole rather than being broken. This is not legal advice: for disposal rules check with B&NES or the council for your own area before sheets leave the garage.
We survey garage roofs in Bath and the towns around it free of charge, photograph your own roof, and afterwards quote you a fixed, written price. If you have a fallen or cracked sheet, tell us when you call on 01225 285181 so we can plan the visit around it. For roof gutters at the same time, see our note on garage gutters.
