How do you re-roof a concrete sectional garage?

A sectional garage is built from precast concrete panels bolted together on site. The walls are the strong part. The roof is the weak part, because it is usually a light covering laid on a low pitch that nobody has looked at for decades. Some are corrugated sheets resting on purlins, which are the horizontal timbers or beams that carry the sheets. Others have a flat deck with a bitumen felt skin.

Start by working out which kind you have. Go inside and look up. Sheets show their ribs from below. A deck shows boards or panels. Note how the roof meets the walls, whether there is a gutter, and whether daylight shows through any joint. We photograph all of this on the survey, because those pictures decide between a patch, a new covering and a full strip back to the frame. If water is coming in now, we cover and dry it first and talk about the full job afterwards.

HSE advises assuming asbestos is present if the garage dates from before 2000. Corrugated cement sheeting on older garages is a typical place to find it. That does not make the garage dangerous while the roof is left alone. It does mean nobody should drill, scrub or break the sheets until someone has identified them, and a lab test on a small sample settles the question.

HSE treats asbestos cement lifted carefully, without being broken up, as non-licensed work. Badly damaged sheets, or sheets that start to crumble, turn it into notifiable non-licensed work, with notice to the regulator before the job begins. Cement garage sheets can fail underfoot without warning, so keep ladders and boots off them. A roof ladder or crawling board spreads the load for any inspection. Wrapped, labelled waste goes in a lockable skip, and a householder's asbestos waste needs a consignment note. Our guide to whether your garage roof is asbestos covers the checks.

If the old sheets are sound and not asbestos, new profiled sheets on the existing purlins are the lightest route. Each sheet type has a lowest pitch it will work at, and the maker's data sheet gives it. Where the pitch is too shallow for sheeting, the better answer is a continuous waterproof membrane over a new deck.

That brings in the choice between rubber, glass fibre and felt. EPDM is a rubber sheet, loose-laid or glued down; one guide gives it 20 to 30 years. GRP is a resin and glass-fibre skin built up in place over boards, which Less puts at 25 to 40 years. Felt is the quickest to lay and the shortest lived, at 10 to 20 years on that same guide. None of those numbers is a guarantee of life, and the finished edges matter as much as the material. Our page on EPDM garage roofs goes through the rubber option in more detail.

Sectional garages tend to dip a little, and water then lies in the low spot. A membrane needs a finished fall so rain leaves the roof. BS 6229:2025 sets a minimum finished fall of 1:80 for flat roofs. Roofers usually aim nearer 1:40 on the drawing, which leaves a margin if the deck moves. Where the old roof has no fall at all, tapered boards or a fresh deck can build one in.

Then the walls. We look at the panel joints, because a cracked joint under a new roof lets water into the wall instead of the gutter. The roof edge gets a drip trim, so water falls clear of the panel face. Where the garage meets a house wall, the junction is dressed with flashing, a strip of lead or metal that seals the gap between roof and wall. We also look at the supports before heavy materials go up, since old panels were never loaded for a modern covering, and we keep stacked materials spread out rather than piled in one spot.

Checkatrade's roof replacement guide, updated October 2026, gives a typical UK range for re-felting a garage roof of about £1,000 to £2,000, with an average of £1,500. Asbestos sheeting, a rotten deck or poor access pushes a job above that, because each adds handling and time. When you compare prices, ask whether they include VAT, scaffolding, waste disposal and testing of the old sheets.

Once we have surveyed the garage, the price comes as one written total for the whole job, and you decide in your own time. Where a patch will hold, we recommend the patch and price that instead of a new roof. Our page on repairing or replacing a garage roof explains how we make that call. The main garage roof replacement page covers the wider job, including how long each stage takes and where the stripped sheets go. We clear the site when the roof is finished, and the waste is taken away.