Start with the old sheets, not the new ones
A concrete sectional garage is built from concrete wall panels with the roof laid over the top. The panels are not the roofing problem. The sheets above them are, because on an older garage those sheets may be asbestos cement.
HSE draws its line at the year 2000: a building put up or refurbished earlier is treated as holding asbestos until shown otherwise. An older sectional garage can fall on the wrong side of it, so a roof of grey corrugated sheets is treated as asbestos cement until someone has identified it.
A sample sent for testing settles the question. MyJobQuote (September 2026) sets an asbestos survey at £325 as its typical cost. Our guide to telling if roof sheets are asbestos explains why a glance from the drive is not enough.
If the sheets turn out to be metal or bitumen, the job is an ordinary re-cover. If they are asbestos cement, HSE describes such roofs as always fragile, so nobody climbs on the roof until a method of working is agreed. A step onto a weathered sheet can end in a fall through it.
What replacement sheets look like, in neutral terms
Several coverings suit a garage roof, and which suits yours turns on the span, the supports beneath and what you want from the building. Rather than favour a product, this table shows what each one's data sheet settles.
| Covering | Check in the data sheet |
|---|---|
| Profiled steel | Minimum pitch, screw spacing |
| Corrugated bitumen | Support spacing, laps |
| Single-ply membrane | Falls, edge trims |
Each product publishes its own minimum pitch, so the slope of the existing frame is set against the data sheet before an order goes in. For a membrane laid flat, BS 6229:2025 allows a 1:80 minimum finished fall, and IKO's advice is to design single-ply roofs for 1:40.
The frame under the sheets deserves the same attention as the sheets. Timbers or purlins that carried the old covering may be rotten, bowed or at a spacing the new product does not accept. That is measured once the old sheets are off, which is one reason the price comes after the look and not before.
Fixings and the details at the edges
Approved Document C of the Building Regulations wants each sheet and tile secured in an appropriate manner. On a garage, that means the fixings the maker specifies, at the spacing it specifies, into the supports it specifies.
A few points decide whether a sheet roof stays put:
- Fixing in the crown or the valley of the profile, as the data sheet directs.
- Sealing washers or caps on every fastener, so water cannot track in along a screw.
- Laps lapped the right way for the weather, with end laps sealed to the maker's detail.
- Edge closures and flashings that stop wind getting under the sheet.
Exposure changes the numbers. A garage squeezed between two houses sees different wind from one on an open plot, and fixings are set out for the site in front of the roofer, not for a standard garage. Met Office averages for Manston (1991 to 2020) show a mean wind of 9.86 knots, against 7.07 knots at inland South Farnborough over the same period.
Rainwater has to go somewhere as well. Our page on a gutter on a garage roof covers the fall and the downpipe.
Cost, and what moves the price
MyJobQuote (October 2026) gives a typical UK range of £750 to £3,500 for replacing a garage roof. That range is wide because garages differ in size, access and material. The same site puts asbestos roof removal at around £2,750, its UK average for taking asbestos off a roof. That figure sits on a separate page for a separate job, so read it on its own and never as a share of the garage range above.
Both figures are national guides, not Castle prices. Which? Trusted Traders and HomeBuilding both report higher prices across London and the wider South East, a region that includes Kent.
What shifts the number on your garage:
- Whether the old sheets are asbestos cement or something else.
- How large the roof is and how tall the walls stand.
- The state of the frame after stripping.
- The new covering you choose.
The survey comes first, then a single total in writing. To compare options before you decide, steel sheet garage roofs are one route worth comparing, and the garage and asbestos roofs hub lists the rest.
