How Long Does Torch-On Felt Last?

Published 6 October 2026 by SA Roofing

What it is: A reinforced bitumen membrane bonded with a gas torch, in at least two layers
Lifespan: Usually 20 to 30 years when well installed
Shortens its life: Ponding, poor upstands, a damp deck and foot traffic
Over old felt: Rarely the best option, as stripping to the deck lets the boards be checked

What torch-on felt is

Torch-on felt is a reinforced bitumen membrane that is softened with a gas torch as it is unrolled, so it bonds fully to the layer underneath. It is the system we use for flat roof repairs and replacements in Dublin, and it is the covering you will find on a large share of the extensions, garages, porches and dormers around the city. The bitumen is modified with polymers, which keeps it flexible in cold weather and stops it softening too much on a warm day, and a polyester reinforcement inside each sheet gives it strength.

A torch-on roof is built up in layers on a sound timber deck, and two layers is the usual minimum on a modern roof. A typical domestic system includes the following.

A vapour control layer, where the roof is insulated, to stop warm, moist air from the room below reaching the insulation.
Insulation boards, on a warm roof build-up.
An underlay or base sheet, the first waterproof layer, bonded to the deck or the insulation.
A cap sheet torched onto the base sheet, with a mineral finish on top that protects the bitumen from sunlight and foot traffic.

How long does a torch-on felt roof last?

A well-installed two-layer torch-on felt roof usually lasts 20 to 30 years in Irish conditions. The membrane is rarely what fails first. Ponding water, a damp or sagging deck, poorly finished upstands and foot traffic shorten its life, while good falls, clear outlets and early repairs to small splits help it reach the upper end of that range. Older built-up felt roofs laid with hot or cold bitumen usually gave around 10 to 20 years, which is why many Dublin extensions from the 1980s and 1990s are now being re-covered.

Our guide to how long a roof lasts in Ireland compares torch-on with other roof coverings. These are the things that shorten the life of a torch-on roof most often.

Ponding water, where the deck has sagged or the falls were never right, so puddles sit on the same patch of felt for days.
Poor upstands and edge details, especially where the roof meets the wall of the house, which is the most common leak point on extensions.
A damp deck under the felt, which leads to blisters as trapped moisture expands in the sun.
Foot traffic from people cleaning windows, fixing satellite dishes or reaching gutters, which can crack the cap sheet.
Blocked outlets and gutters, which back water up onto the roof.

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Can torch-on felt go over old felt?

It is sometimes possible to torch a new layer over an existing felt roof, but it is rarely the best option on an older Dublin extension. An overlay only works when the old covering is firmly bonded, dry, free of blisters and laid on a sound deck. If there is moisture trapped in the old layers or in the boards beneath, a new membrane seals it in, the new felt blisters, and the deck carries on rotting out of sight.

Stripping the old covering back to the deck lets the boards be checked and replaced where needed, the falls corrected and insulation added if you want it. It costs more at the time, but it gives the new roof its full life. Our article on flat roof repair versus replacement covers how to judge the condition of an existing roof.

Torch-on compared with cold-applied and self-adhesive felt

Some parts of a roof do not suit a naked flame. Cold-applied systems use a bitumen adhesive instead of heat, and self-adhesive membranes have a sticky backing that bonds when the release film is peeled off. They are useful where torching would be unsafe, such as against timber cladding, fascias or rooflights and in tight corners, and on some roofs they are used for the edges and details while the main area is torched.

On an open roof with a sound deck, a fully torched system gives a very strong bond, with seams fused together rather than glued. The right choice depends on the roof, and a mix of methods on one roof is common.

Torch-on compared with EPDM and GRP

EPDM rubber and GRP fibreglass are also used on Irish flat roofs, and both perform well when laid by someone who works with them regularly. Torch-on suits the small extension, garage and dormer roofs most Dublin homes have, and our flat roofing page compares torch-on, EPDM, GRP and PVC membranes side by side.

Fire safety on domestic roofs

Torch-on is hot work, carried out with an open flame on a roof that may sit next to timber fascias, cladding, insulation and plastic gutters. A careful installer plans the job around that. The flame is kept away from anything combustible, cold-applied or self-adhesive products are used at the risky details, an extinguisher is kept on the roof, and the area is checked for anything smouldering after torching has finished. When you are comparing quotes, it is reasonable to ask each contractor how they manage fire risk on your roof.

Looking after a torch-on roof

A torch-on roof needs very little maintenance, but a little attention once or twice a year helps it reach the upper end of its lifespan.

Keep outlets, gutters and the roof surface clear of leaves, moss and debris, especially in autumn.
Avoid walking on the roof, and use a board to spread the load if you have to.
Look for blisters, splits, bare patches where the mineral finish has gone, and gaps at the upstands.
Check the ceiling below for stains after heavy rain.
Have small defects repaired before the winter, while the deck underneath is still dry.

Getting a quote

Our guide to flat roof repair costs in Dublin explains what drives the price of a repair or a new roof. If your flat roof has a blister, a split or a soft patch, send a photo on WhatsApp and we will tell you whether it looks like a patch or a strip and recover, then confirm the price after a free inspection.

Frequently asked questions

Is torch-on felt any good?

Yes, when it is installed properly. A two-layer torch-on system on a sound deck with good falls is a durable, repairable covering for the extensions, garages and dormers that make up most Dublin flat roofs. Most failures come from poor details, a damp deck or ponding rather than the membrane.

What are the downsides of torch-on felt?

It needs a naked flame, so it has to be laid carefully near timber and other combustible materials, and it needs dry weather to bond properly. It relies on lapped seams that must be fully sealed, and heavy foot traffic can damage the cap sheet.

Is it better to overlay old felt or strip it first?

Stripping is usually better. An overlay only works if the old felt is dry, firmly bonded and on a sound deck, which is rare on older roofs. Stripping lets the deck be checked and repaired and the falls corrected before the new felt goes down.

Is torch-on felt better than self-adhesive felt?

Torch-on gives a very strong, fused bond on an open roof, while self-adhesive and cold-applied felts are safer where heat cannot be used, such as against timber or cladding. Many roofs use torch-on for the main area and a cold or self-adhesive product at the details.

Does torch-on felt need maintenance?

Very little. Keep the outlets and gutters clear, avoid walking on the roof, and have blisters, splits or lifted edges repaired early so water does not reach the deck.

Do I need an underlay for torch-on felt?

Yes. Torch-on is a system of at least two layers: a base layer or underlay bonded to the deck, with a mineral-finished cap sheet torched on top. A single cap sheet on its own is not how the system is designed to be laid and does not last as long.

Torch-on felt roofs: how long they last and what to expect