How Long Does a Felt Flat Roof Last?

Felt is a catch-all name for sheets of bitumen reinforced with a fabric core, laid in overlapping layers over a deck. The two systems you meet most are quite different roofs.

The older kind is built-up felt. Three layers are laid on a hot bitumen coating, each stuck to the one below, with chippings or a mineral top layer to protect the surface. Many flat-roofed garages and extensions in Crawley's post-war neighbourhoods were finished this way. It was cheap and quick, but the cheap grades were prone to splitting as the felt dried out and the bitumen aged.

Modern torch-on is a manufactured system. Two or three layers, usually a base layer and a reinforced cap sheet, are heated with a gas torch so the underside of the sheet melts and bonds. The cap sheet often has a granular finish, and better grades carry a polyester or glass reinforcement that resists tearing and movement. The key difference is not the flame; it is the quality of the sheet and the way the laps, upstands and edges are detailed. A good torch-on roof is a different product to a thin, tired layer of old felt.

The best available published figure is Less, in an update dated March 2026, which gives felt as 10 to 20 years. Read it as an average spread across many roofs, since no roof is guaranteed that age. A warranty period is not a lifespan, and some roofs fail early while others see out the top of the range.

Several things push a roof toward the short end. Standing water is the biggest: puddles hold moisture against the surface and speed up the ageing of the bitumen. Heavy foot traffic, a wet or movement-prone deck, and shaded areas that stay damp all shorten life too. So does a roof laid in winter on a damp deck, where moisture is trapped beneath the felt and later forms blisters.

Poor detailing at the edges is the other big cause. If the felt is not turned up properly where it meets a wall, or the drip edge is loose, water finds the gap while the open surface is still sound. Regular checks help: clear the outlet, keep leaves off the surface, and look for lifting at laps after storms. Our answer on flat roof ponding water shows why puddles matter so much.

Some marks are easy to see from a window or ladder. Surface cracking that looks like crazed paving, called alligatoring, shows the bitumen has dried out. Open laps, where one sheet has peeled away from the next, let water straight in. Bare patches where the chippings or granules have washed off leave the sheet exposed to the sun. Blisters that crack open, or that sound hollow underfoot, mean moisture has crept beneath.

Inside, look for ceiling stains that return after a repair, a musty smell or bubbling paint. If a patch has failed twice in the same area, the felt around it is usually tired as well. A repair is the better buy when one section has failed and the rest is supple; once the surface is brittle, each patch just moves the weakness elsewhere.

Blistering has its own causes, covered in flat roof blistering. For help deciding between patching and starting again, read repair or replace a flat roof. An old built-up roof that has reached the end of the road is usually better replaced than nursed through another winter.

Replacing a felt roof usually means stripping the old layers, checking the deck and renewing any boards that are damp or soft. If new insulation goes in, it is worth asking your building control body how Part L of the Building Regulations applies to your roof.

Checkatrade's September 2026 rubber roofing guide puts felt at £50 to £80 per m² as a typical national range. Yours depends on the area, access, the layers chosen and whatever lies under the old felt. The single written price comes once the survey has shown what the old layers are sitting on.

Timing helps the new roof last. Felt goes down best on a dry deck in settled weather, so a good roofer checks the boards for moisture before the first sheet is laid, and sets up the work so rain cannot get under an open section. Ask how the edges, outlets and upstands will be finished, since those are the places where an older felt roof usually fails first.

Many owners compare felt with other coverings at this point. Modern felt is a reasonable choice, but it is not the only one; EPDM and GRP each have their place. Our flat roofing page sets out the wider options and what each suits.