A garage with a grey corrugated roof, mossy and a little cracked, is a familiar sight across Hampshire and Berkshire. Many of those roofs are asbestos cement, and the owners tend to hear two opposite messages: that the roof is a deadly hazard that must be taken off by specialists at enormous expense, or that it is harmless and can be ignored. Neither is quite right. This guide explains what asbestos cement is, what the rules actually say about removing it, how a careful job is done, what it costs, and the situations in which the best decision is to leave it in place or cover it over.
What you are dealing with
Asbestos cement is a mixture of cement and asbestos fibre, pressed into corrugated sheets, flat sheets, pipes and gutters. It was widely fitted to garages, sheds, farm buildings and industrial units for much of the twentieth century because it was cheap, light, fireproof and durable. The fibres are bound into the cement, which is why intact sheets are considered a lower risk than loose asbestos materials such as lagging or sprayed coatings. The danger arises when sheets are broken, drilled, sanded, scrubbed with a wire brush or blasted with a pressure washer, because that releases fibres that can be breathed in and lodge in the lungs.
Weathering matters too. An old roof grows moss and lichen, and its surface slowly erodes. A weathered sheet can shed fibres more easily than a fresh one, and it is more brittle, so it is more likely to snap if someone walks on it. Our guide to how to tell if your garage roof contains asbestos explains the visual clues and why only a laboratory test can confirm it.
What the rules say
The HSE separates asbestos work into licensed, notifiable non-licensed and non-licensed categories. Careful removal of asbestos cement roof sheets, where the sheets are handled without being broken up, is non-licensed work. It becomes notifiable non-licensed work if the material will be substantially broken up, for example by dropping or smashing a roof, and the work then has to be notified to the enforcing authority beforehand. In every case a risk assessment, appropriate controls and trained workers are needed, and the waste has to be dealt with as hazardous waste. The HSE explains the categories on its page about non-licensed asbestos work.
One myth is worth correcting. Plenty of websites tell homeowners that a licensed contractor is compulsory for any asbestos garage roof. For careful removal of cement sheets, that is not what the HSE says. What the HSE does require is that the work is planned, assessed and done by people who know what they are doing, which is a different thing from needing a licence. If other materials are present, such as asbestos insulating board in a soffit or lining, the position changes, since higher-risk materials do need a licensed contractor. Our short answer on whether asbestos cement removal needs a licence goes through it.
The removal process, step by step
A well-run job follows a sequence, and each stage exists for a reason.
- Survey and sampling. We inspect the roof, the supporting structure, and any other suspect material. If the roof is not already known to be asbestos cement, a sample goes to a laboratory.
- Planning. We decide how the sheets are fixed, how they will come off whole, where the waste will be staged, and how people will reach and leave the roof safely. A written risk assessment sets out the controls.
- Preparing the area. Vehicles and belongings come out of the garage, the ground below is covered, and the work area is marked off.
- Taking the sheets off. Sheets are lightly wetted to suppress dust, unfixed rather than snapped, and lowered by hand. Roof access uses crawling boards or similar, never walking on the sheets themselves.
- Wrapping and labelling. Sheets are stacked, wrapped in heavy polythene, sealed and marked as asbestos waste. Debris and used protective items go in labelled bags.
- Cleaning. The area is cleaned with wet methods or a suitable vacuum, not swept dry.
- Removal of the waste. The wrapped sheets leave the property as hazardous waste. Our guide to disposing of asbestos roof sheets in Hampshire covers where they go.
- The new roof. Once the structure is checked and repaired, the new covering is fitted.
What affects the cost
Published figures from third-party cost guides are scattered and thin. One specialist asbestos site reports typical UK ranges of £1,200 to £2,000 for removing and disposing of a single garage roof, and £2,500 to £4,500 for a double. That comes from a single vendor, so treat it with caution, not as a price list. These figures normally cover removal and disposal of the old sheets only. The new roof is on top: a separate guide puts an EPDM roof on a single garage at a typical UK range of £1,200 to £2,500 fitted. Your fixed quote follows the survey.
The factors that move the price are these:
- The size of the roof and the number of sheets.
- How the sheets are fixed, and how hard they are to release.
- Access, including whether a scaffold or tower is needed for a tall or awkward garage.
- The condition of the sheets, since brittle ones take more care.
- Whether other asbestos materials are present, such as a flue pipe or soffit board.
- The condition of the timbers underneath, which are often damp or rotten after years of condensation.
- The choice of replacement roof, from a simple membrane to a pitched tiled roof.
For a view of the cost of the new roof as well, see our garage roof replacement cost guide.
Is removal always necessary?
Not always. If the sheets are sound, not cracked or crumbling, and the roof is not leaking, leaving them undisturbed is a legitimate choice. Asbestos cement that is intact and left alone releases very little. The roof does need watching, and moss should not be scrubbed off. There are two other options before full removal.
Overlaying means fitting a new covering over the existing sheets without disturbing them. The HSE task guidance for small structures such as garages mentions overlaying as something to consider, but it does not apply where other asbestos materials are present, and the structure has to cope with the extra layer. It also leaves the problem for the future, since someone will eventually have to take the whole lot down. Encapsulation, painting the sheets with a sealant, has its place on sound roofs, though it needs a proper survey and is not a repair for leaks. Our answer on sealing an asbestos roof explains the limits.
The structure under the sheets
Once the sheets are off, the frame is exposed to daylight for the first time in decades, and it often tells a story. Corrugated roofs are usually carried on timber purlins (the horizontal beams that span between the gable walls) or on rafters at wide spacing. Years of condensation on the underside of the sheets drips onto the timber and keeps it damp. We commonly find rot at the ends of the purlins where they bear on the walls, soft patches where old fixings corroded, and sagging where a beam has been overloaded by moss and water.
A new roof can only be as good as what carries it. If a sheet roof is replaced by a heavier covering, such as tiles, the frame may need strengthening. If it is replaced by a lightweight membrane, the deck below must be sound, falls must be right, and the walls at the top may need a new wall plate. All of this is checked during the survey and again when the old roof is off, and any extra work is explained and priced before it goes ahead.
Working safely on a fragile roof
Asbestos cement sheets are brittle, and a weathered sheet will not take a person's weight. Falls through fragile roofs are a leading cause of serious injury in roof work, so the access method matters as much as the dust control. Crawling boards or a platform spread the load across the structure, edge protection guards the perimeter, and nobody steps directly on a sheet. A roof that looks solid from the ground can be treacherous, particularly where moss hides a crack. It is another reason to leave the job to people with the equipment and training for it.
Doing it yourself
It is not illegal for a homeowner to remove asbestos cement from their own garage, but the practical problems are serious. The roof is fragile, the sheets are awkward, the dust controls and protective equipment need to be right, and the waste has to be packaged and delivered correctly. A fall through a weathered roof is the other hazard. Most people find that the cost saving is not worth it. We set out what is involved in our answer on removing an asbestos garage roof yourself.
What goes on the roof afterwards
With the old sheets gone, you have a choice of replacements. A flat or low-pitch roof in EPDM or GRP is quick and neat. A felt system is the cheapest. Profiled metal or fibre-free cement sheets keep the look of the original. A pitched tiled roof suits a garage you want to match to the house, though it needs more structure. Whatever goes on, we look at the timbers first, because rafters that have sat under a leaking roof for years are often damp or decayed. Our guide to garage roof options compares the choices.
Next steps
If your garage roof is grey, corrugated and dates from before the late 1990s, it is worth having it looked at. We begin with a free survey and photographs of your own roof, and confirm what it is made of. The quote that follows is fixed and written, and it spells out removal, disposal and the new roof as separate items. A written guarantee on our workmanship lasts ten years. Read about the service on our garage roof replacement in Basingstoke page, or phone 01256 213956.
