How long does a felt flat roof last?

Two published ranges for torch-on felt

Torch-on felt is bitumen sheet laid in one or more layers and bonded to the deck by melting the underside with a gas torch. Of the usual flat roof coverings, it carries the lowest published life, which is why a felt roof is the one most worth inspecting as it nears ten years.

Two cost guides publish a figure, and they do not agree exactly:

Both start at 10 years, so a felt roof close to a decade old deserves a proper look from above. The top of each range is what a well-built, well-drained roof might reach, not what any roof is owed. Treat the range as a planning guide for the roof, not a warranty, and a maker or contractor who offers a warranty is making a separate promise. For the other coverings side by side, see the flat roof lifespan comparison.

What pulls a felt roof towards the short end

Felt is a thin skin, so what happens at the surface matters more than it would on a thick covering. These are the things that tend to cost a roof its years:

• Water that stays put. A roof with ponds after rain, or a blocked outlet, keeps the membrane wet far longer than one that drains.
• Foot traffic. Anyone who uses the roof as a path to clean a window or reach an aerial scuffs the surface and opens the laps, which are the overlaps between sheets.
• Weak detailing. Edges, the upstand where the sheet climbs a wall, and the flashing above it take the movement and fail first.
• A single thin layer on a deck that was never well fixed, where the sheet follows every ripple in the boards.
• Cold cycles. Manston logs an average of 21.43 air-frost days a year (Met Office, 1991 to 2020), and every freeze and thaw works on a laid joint.

These are conditions around the felt, not flaws in the felt itself, which is why two roofs laid in the same summer can age at very different rates. A roof kept clear and well drained has the better chance of the upper end.

Signs that a felt roof is near the end

A felt roof rarely fails in one afternoon. It gives warnings, and reading them early is the difference between a repair and a strip. Look for these from a safe position, such as an upstairs window or a ladder held by someone else:

1. Blisters, the raised bubbles that crack open and let water in. The blisters guide covers what each size means.
2. Splits along the laps or across the sheet, often where the roof meets a wall.
3. Surface crazing, where the top skin breaks into a pattern of small cracks and the grit has gone from areas of the sheet.
4. Soft or springy patches underfoot, which point to wet boards below.
5. Brown stains on the ceiling underneath, or a damp smell after rain.
6. A history of patches, with a new one needed every year or two.

One blister is a job for a patch. Several signs together, or a roof already past 10 years with a patch history, usually mean the covering has done its time. The wider list of failure signs helps you tell the difference.

Patch, coat or renew

If the deck is dry and the damage is local, a patch is the sensible buy. Where the surface is tired but sound, a coating can add some time, and the coating guide explains when that holds and when it only hides a problem. If the felt has split in several places or the boards are wet, the covering comes off and the deck is checked before anything new goes down.

For scale, Which? Trusted Traders (November 2025) gives £1,400 to £3,500 for a felt covering on a roof measuring 6m by 3m over a single garage, ex VAT. Which? also notes higher prices across the South East, the region that includes Kent. That is a typical UK range, not a price for your roof.

The decision begins on the roof itself, so the first step is a survey. Photos of the surface, the edges and any ceiling stains tell us a good deal before anyone climbs a ladder. Our flat roofing page lists the work we carry out on flat roofs, from repairs and coatings to full replacements. Whichever route suits, the old felt and the waste leave site with us when the job is done.