If you have bought a house with an old garage, or inherited one, you have probably wondered about the corrugated grey roof. Asbestos cement was a common garage roofing material for much of the twentieth century, so the suspicion is reasonable. The honest position is that no one can be sure by looking. Some sheets that look identical are fibre-free, and some that look like harmless cement contain asbestos. What you can do is weigh the clues, avoid anything that disturbs the roof, and get a sample tested if the answer matters, which it does before any work. This guide explains the clues and the safe way to resolve them.
Start with the age of the garage
Age is the strongest clue. Asbestos cement was used widely in UK buildings through the middle of the twentieth century, and its use was phased out and then banned, with the final prohibition coming at the end of the 1990s. A garage built or re-roofed before then could well have an asbestos cement roof. One built or re-roofed afterwards is unlikely to, though not impossible if old stock or reclaimed sheets were used. If you know when the house was built, the garage is probably the same age or a bit later, and any paperwork from a previous owner may state when the roof was last replaced.
The difficulty is that garage roofs are replaced without records. A roof that looks old may be newer than it seems, and a roof that looks tidy may be original. Treat age as a prompt to look further, not as an answer.
What the roof looks like
Certain features raise suspicion. Large corrugated sheets, grey or dull off-white, with a rough cement-like texture, fixed with bolts or screws that have large washers, are typical of asbestos cement. The sheets are heavy for their size and thick at the cut edges, which look like fibrous cement. Weathered sheets are often covered in green or black lichen and moss, and the surface may look pitted or flaky. Many sheets were laid in a standard corrugated profile in a long, low-pitched run over timber or concrete purlins. Some were painted or coated, which can hide the surface.
Other roofing materials can look similar from the ground. Modern fibre-cement sheets without asbestos, corrugated bitumen sheets, plastic and galvanised steel all resemble each other at a distance. Galvanised steel rusts and rings if tapped, bitumen sheets are black or brown and flexible, and plastic is translucent or coloured. None of that turns a suspicion into a fact.
Other parts of the garage to check
Asbestos cement was not limited to roof sheets. Look at the rest of the building for clues that the same materials were used.
- Gutters and downpipes that are heavy, grey and square or half-round in cross-section, possibly with cement-like joints.
- Flat sheets used as fascias, soffits or cladding on the gable ends.
- A flue pipe passing through the roof, if a heater or boiler was once in the garage.
- Flat grey sheets lining the walls or ceiling.
- Water tanks or storage cisterns of grey cement in the roof space.
Asbestos insulating board, a different and softer material, was used for ceiling and wall linings and for soffits, and the HSE treats it as higher risk than cement. If you suspect it, do not disturb it. The difference between the two materials is set out in a separate answer about asbestos in soffits.
What not to do
The most important advice is about what to leave alone. Do not drill, saw, sand, scrub, scrape or pressure wash the roof to see what lies beneath. Do not snap off a corner to look at the cross-section. Do not walk on the sheets, which may be brittle and can fracture, putting you at risk of a fall as well. Do not use a wire brush to clear moss. Do not burn or smash old sheets. Each of these releases fibres, and the damage is done by breathing them in. The safest course with an unknown roof is to treat it as asbestos until you have proof otherwise and leave it undisturbed.
It is also not a good idea to ask a friend with a van to take the sheets away if you only suspect asbestos. The waste has to be handled and packed correctly, and our guide to disposing of asbestos roof sheets in Hampshire explains why it cannot go in a skip.
Paperwork and other sources of evidence
Before paying for a test, check what records exist. The seller's information pack may mention the garage roof, and a survey carried out when you bought the house may have flagged it. Planning or building control records at the council can show when the garage was built, which is a guide to the likely roof material. If the garage is a manufactured kit, the maker's name may be stamped on a panel or post, and the type of kit tells you what roofs were offered. A neighbour with an identical garage on the same estate may know what theirs turned out to be, since estates were often built with the same details. None of this is conclusive, but it can move a suspicion towards a probability and help you decide whether to test.
When the sheets are a bigger concern
Intact sheets are a lower hazard than damaged ones, so condition matters as much as identity. Be more concerned if the sheets are cracked, crumbling at the edges or broken, if a tree branch or storm has damaged them, if the surface is eroded so the fibres show, or if children or pets play in the garage. A sheet roof that has deteriorated can shed small fragments onto the floor and into the gutter. If you find loose pieces, do not sweep or vacuum them. Keep people out and get advice on safe clearance. A roof that is in good order, undisturbed and sealed from the interior, is a different case, and leaving it alone can be a sound decision.
What the test result does not tell you
A laboratory report answers one question: does this sample contain asbestos? It says nothing about the rest of the building. A garage with an asbestos cement roof may also have an old fibre board lining, and a garage with a clear result on the roof may have a flue pipe or gutter made of something else. If you plan work beyond the roof, ask for each suspect material to be sampled separately, and ask that the report identify which sample came from where. A short list of positions with photographs and a plan is easy to produce at the survey stage and avoids surprises once work starts.
Landlords, tenants and shared garages
If the garage is let, or part of a block of garages shared between neighbours, responsibility is less clear. A landlord has duties for the condition of the property, and shared blocks usually have an agreement or management arrangement about the roof. Raise the question in writing, and do not let anyone work on the roof until its material is known. If a sheet is broken and you do not control the building, the managing party should be told straight away.
How a sample settles it
The only reliable way to know is to have a small sample analysed in a laboratory. A trained person takes a piece from an unobtrusive spot, usually a broken edge or a corner that is already damaged, with the area dampened to limit dust, and seals it in a bag. The lab examines it under a microscope and reports whether asbestos fibres are present and of what type. Results usually take a few days. The cost is modest compared with a roof job, and the result tells you what rules apply to the work.
It is best to use a lab that is accredited for asbestos analysis, and to have the sample taken by someone who knows how to do it without releasing dust. Our answer on testing a garage roof for asbestos covers how sampling works and what to ask for.
If it is asbestos cement
A positive result is not an emergency. Intact asbestos cement that is left undisturbed releases little. Our answer on whether an asbestos garage roof is dangerous explains the risk. You then have choices. You can leave the roof in place and monitor it. You can have it overlaid, which the HSE task guidance for small structures mentions as an alternative to removal, if the structure is suitable and no other asbestos is present. Or you can have it removed carefully. HSE guidance classes careful removal of whole sheets as non-licensed work, and expects the work to be assessed in advance, carried out with dust controls and done by workers who have been trained for it. It becomes notifiable if the sheets are to be broken up substantially. Costs and the sequence of work are covered in the longer piece on removing an asbestos garage roof.
If it is not asbestos
A negative result also tells you something: the roof can be repaired or replaced like any other, without the special handling. It is still worth checking the condition of the sheets, the fixings and the frame. Many old non-asbestos sheets are cracked and brittle, and the timbers below may be rotten. Our guide to garage roof repair or replacement shows how to judge the next step.
Why it matters when you sell
A buyer's surveyor will notice an old corrugated roof, and may mention asbestos in the report. Having a test result in hand, or a record of proper removal, spares you a delay and a price negotiation. If you are thinking of selling, read our answer on selling a house with an asbestos garage roof.
Getting someone to look
If you want a professional opinion, we can look at your garage as part of a free survey. We photograph the roof from a safe position, assess the sheets, the frame and the details, and, where there is doubt, arrange a sample for testing before any decision is made. We do not disturb the roof in order to look at it. You get a plain report, and if work is needed, a fixed written quote. Any roof we then build carries a written ten-year guarantee on workmanship. Our service page for garage roof replacement in Basingstoke explains the range, and the number is 01256 213956.
