How are carport and lean-to garage roofs replaced?

A lean-to garage or carport has one slope, which rises to a house wall at the back and drops to a gutter at the front. That simple shape hides three weak points. The top edge meets a wall that moves differently from the roof. The slope is often shallow. And on a carport, the sides may be open, so wind blows under the roof as well as over it.

Most of these roofs are fixed to a thin timber frame or a steel one, and carried on posts or a low wall. The covering might be corrugated sheeting, polycarbonate, boards under felt, or a modern membrane. Each wants a different minimum slope, so the first thing we do is measure the fall and read the manufacturer's data sheet for whatever is on the roof now. We also check the posts and the fixings to the house wall, because new sheets on rotten timber simply move the leak.

Corrugated sheets of cement, metal or plastic are quick to fit and light, which suits a frame that was never built for much weight. Polycarbonate lets daylight through, which helps where the carport doubles as a sitting area. Guides put a polycarbonate conservatory roof at around 10 to 15 years, and a clear carport roof is a similar product, so budget for a shorter life than a solid covering.

Where the roof is shallow, or leaks have rotted the boards, a continuous membrane on a new deck is usually the answer. EPDM is a rubber sheet rated at 20 to 30 years in one guide, and GRP, a glass-fibre and resin skin, at 25 to 40 years in another. Slate or tiles are possible on a sturdy lean-to with the right pitch, but the weight has to be checked first. If the roof is now heavier by about 15 per cent, the Planning Portal says building control approval is needed. Our page on the best garage roof material compares the families side by side.

Where the roof meets the house, water runs down the wall and onto the roof. The usual cure is a flashing, a band of lead tucked into a slot cut in the wall and lapped over the new covering, which sends rain across the joint instead of through it. If the old flashing is split or lifted, it is replaced when the roof is renewed, because a new covering under a failed junction would leak again within a season. The same goes for any cement fillet, a sloping triangle of mortar that was once used to close the gap and now tends to crack away.

At the other end, the gutter edge needs a clean fall so water reaches the outlet. The roof edge is finished with a drip trim or a fascia board so the covering does not curl. If the carport's gutter drains onto a drive or neighbour's boundary, check where the downpipe discharges. Our guide to leaking garage roofs shows how to trace a leak to one of these junctions before anyone strips the whole roof. A leak at the wall is repairable more often than owners expect.

Marley warns that where a roof is pitched at less than 30 degrees, the slope facing the wind may suffer strong negative pressure. A carport has a shallow slope and open sides, so the roof is pulled up from below as well as pressed down from above. Fixings go through the sheet into the frame at the spacing the maker gives, and a fixing that looks neat but only grips a thin rail will lift in a gale.

We also check the connections between roof frame, posts and the house. Rusty brackets and split timber are cheap to replace while the roof is open, and expensive to find afterwards. Birds sometimes nest in open carports, and the law protects both nesting birds and bats, so we look before stripping. Before work starts we also agree where the old sheets will go, so the drive is not left littered with offcuts.

Checkatrade puts a typical UK garage re-felt at about £1,000 to £2,000, with an average near £1,500, in its roof replacement guide updated October 2026. A carport or lean-to is a similar size of job, though the choice of sheet or membrane shifts the total. Access matters too. If a ladder reaches the roof from a drive, the job is simpler than one that needs a scaffold standing on a public pavement, where the county council, as highway authority, must grant a scaffold licence. Ask whether any quote includes VAT, scaffolding and taking the old roof away.

We survey the roof, photograph each problem and send a written quote giving one total. When a repair will hold the roof for years, we recommend the repair, and we say what it will not cure. Our garage roof cost page and the wider garage roof replacement page show how prices are built up and what the work involves.