Can a felt garage roof be repaired?

Felt roofs on garages are usually built-up bitumen felt or a torch-on system, laid in layers over boards. Most faults begin at an edge or a joint rather than mid-sheet. A lap that has opened, a corner where the felt has lifted in a gale, a puncture from a branch, or the strip against the house wall where the upstand has peeled away are all repairable in a visit.

The test is simple. If the felt around the fault is still supple, takes a weld when warmed and shows no sign of widespread cracking, a well-made patch will outlast the rest of the roof's life. A strip of new felt is welded over the damaged area, extending well beyond it on every side, and the edge is sealed. Done properly, a patch of that sort restores the waterproofing without a bill for a new roof.

Where the roof allows it, we propose exactly that. Pictures of the damaged patch, the wall junction and the roof as a whole tell us quickly.

Look for the signs that say patching is wasted money.

• Blisters. Raised bubbles mean trapped moisture or air. A few small ones can be cut and sealed, but dozens across the roof mean the layers have parted company.
• Crazing and cracks. A surface that has gone like crocodile skin has lost the oils that kept it flexible.
• Splits along every lap. One open seam is a repair. A line of them is movement in the deck or a covering that has aged out.
• Soft boards. If the roof gives underfoot, or the boards are stained, black or crumbling from below, the deck needs replacing before any covering will last.
• Ponding. Standing water that lingers days after rain shows poor fall and speeds up ageing.

Sources disagree on how long felt lasts. Less puts torch-on felt at 10 to 20 years, saying a good job can reach 20 and a poorly laid roof may fail before year ten. CORC suggests more than that where the roof is well maintained. Treat any such figure as a range, not a promise.

Re-felting begins with lifting the old covering and inspecting the deck, swapping any boards that are rotten or loose, and laying a fresh system. Torch-on felt is applied in two or three layers, the layers welded together with a gas flame, and the edges dressed over drip trims. A cap sheet finishes the surface. Against a house wall, an upstand and flashing carry the felt up the brickwork, chased into a mortar joint or sealed.

Done properly it also lets you fix the things the old roof got wrong. If the roof never had enough fall, the deck can be furred up to improve drainage. IKO, quoting BS 6229:2018, gives 1:80 as the recommended minimum finished fall, with 1:40 as the design target so the roof ends up above that line. Guttering and a rainwater outlet can be tidied at the same time.

Some owners take the chance to move to a different material altogether. Our page on turning a flat garage roof into a pitched one looks at the bigger change.

National guides give an idea of scale. Checkatrade's roof replacement page, updated October 2026, suggests about £1,000 to £2,000 to re-felt a garage roof, averaging £1,500. MyBuilder's garage roof guide, updated August 2026, gives felt at about £75 per m², and a single flat garage roof replacement in the range of £700 to £1,000. A repair costs a fraction of those figures, but a patch is priced on survey, so plan around the number in your written quote.

Several things shift the price: roof area, board replacement, the number of layers to strip, waste removal and access to the building. Look for VAT and scaffolding in any quote you hold. A felt roof near a boundary wall or under a tree can be slower, and a roof against a house wall takes more flashing work.

If the garage is old, remember that some older sheets and soffits contain asbestos. Our guide to asbestos garage roof removal and the law explains what changes.

A great many felt roof failures are really water management failures. If rain pours over the edge and runs down the wall, it soaks the fascia and the roof margin, and the felt lifts there first. A split or leaking gutter fills the wall junction with damp and loosens the felt at the abutment. Fix the water route and the roof lasts longer. Our page on whether a garage needs guttering goes through when it matters and what to fit.

Look at the drip edge too. Felt should finish over a metal or plastic drip trim so the water clears the fascia, rather than curling back underneath. Check the top edge against the wall for a gap, a missing flashing or mortar that has fallen out. These small details cost little to put right and are often the actual cause of the stain on the garage ceiling.

Our survey begins with pictures taken at the fault, at the wall junction, across the surface and, where we can, from underneath. We then say whether a repair will last or a re-felt makes more sense, and give our reasons.

Our written total arrives after the survey, backed by a ten-year guarantee on the workmanship, and we carry off the old felt. If a repair is the right answer, that is the quote you get; we do not push a new roof to enlarge the job. Send photographs by WhatsApp, use the enquiry form or ring 01793 626096. Other garage coverings are compared on our garage roof replacement page.