Is built-up felt still used on commercial roofs?

Felt has not disappeared because it does a job that suits plenty of buildings. It is a layered covering that can be dressed round pipes, rooflights, parapets and corners, so it copes well on small, broken-up roofs where a large rolled sheet would need many cut-outs. A shop with a rear extension, a unit with a lean-to, the flat roof over a stairwell: these are the places where felt is still specified.

It is also a covering that roofers know well, and repairs are usually simple. A split, a lifted lap or a tired upstand can often be cut out and patched without stripping the whole roof. That matters to an owner who wants to spread the cost or keep the business trading while the work goes on.

The weakness is that the result leans heavily on whoever lays it. Less (March 2026) says careful laying can carry felt towards 20 years, and that careless work may see it give up before year 10. Knowing that before you pick a roofer tells you more than any brochure will.

A built-up felt roof goes down in stages. A base layer is fixed to the deck first, then a further layer or two, and a mineral-finished cap sheet goes on top to take the sun and the weather. Each layer is stuck to the one below and to the deck, using a gas torch, hot bitumen or cold adhesive, depending on the system and what lies underneath.

The joins and edges matter more than the open areas. Water finds the laps between sheets, the upstands (the part of the covering that climbs a wall or a rooflight kerb), the edge trims and the outlets, so a felt job is really judged on how those details are finished. An upstand has to be sealed under a flashing or cover strip so rain cannot run down behind it.

The survey settles which fixing method suits your roof. A torched layer over a timber deck calls for more care about fire risk than a cold-applied layer over concrete, and we would explain which one we propose, and why, before any figure is written down.

Lifespans are ranges, never promises. Less gives 10 to 20 years for felt, while CORC puts a well-made felt roof at 30 years or more. The sources disagree because the roofs they describe were laid and looked after differently.

Several things push a roof towards the short or the long end of its range. Falls that let water leave the roof quickly help a great deal. So does keeping gutters and outlets clear, limiting foot traffic to a marked route, and mending small splits before water gets under the cap sheet and into the insulation. Standing water and repeated patching age a roof faster.

A sensible rule of thumb: when the same corner or outlet keeps needing attention, the covering around it is usually tired. Our answer on how long a commercial roof lasts compares felt with EPDM, GRP, tile and zinc. A sensible habit is to begin pricing a replacement when the same areas keep failing, rather than waiting for an emergency leak into stock or a customer area.

Most early failures on flat roofs start with water that stays put. BS 6229:2025, which replaced the 2018 edition in December 2025, keeps a minimum finished fall of 1:80. A designer will normally aim for about 1:40, since a deck built to exactly the minimum can end up with shallow dishes once the structure moves and the layers are added.

Standing water does not always leak straight away. It holds grit and algae against the surface, sits on laps for days and speeds up the ageing of the cap sheet. If your roof ponds, the fix may be new falls formed in tapered insulation or a re-laid area rather than yet another patch. Our guide to ponding on commercial flat roofs explains how we tell a harmless puddle from a drainage fault.

At the survey we photograph the dips, the outlets and the laps nearest them, and you get those pictures so the problem is plain to see.

Felt and single-ply membranes suit different buildings, and neither wins every time. Single ply arrives as large sheets with welded or sealed joins, so it often goes down faster on a big, simple roof with few details. Felt tends to make more sense where the roof is small, heavily detailed or hemmed in by walls, and where the owner wants the option of local repairs later.

Read our explanation of single-ply roofing to see how the two compare on joins, repairs and cost drivers. Whatever the covering, the deck, the insulation and the drainage under it set how long the new roof will perform.

The survey decides the recommendation. We examine the deck, test for wet insulation, take photographs of each defect and give you a clear call: patch it, or re-cover it. A written quote with the total follows. Our commercial roofing page sets out the wider range of work.