Is Torch-On Felt Safe?

Torch-on felt is bitumen sheet that is melted onto the roof with a gas torch. The sheet is heated until the underside turns glossy and flows, then pressed down to bond. That flame, and the very hot bitumen it makes, is what sets this method apart from other flat roof coverings, and it is the source of the danger.

Flat roofs are usually built on a timber deck, with a gap beneath for insulation or ventilation. Heat can pass through a joint between boards, along an upstand, behind a fascia or into the eaves where it meets old, dry timber or insulation. A smouldering fire in a hidden void may not show for an hour or two after the roofer has packed up and gone, and then spreads before anyone notices. The roof is out of view, there is often nobody looking at it, and the fire can be well advanced by the time smoke appears.

The risk is not the roof surface burning in the open. It is concealed fire in the build, which is why where and how the flame is used matters far more than the material itself. A careful roofer treats every torch as a hazard.

Many roofers divide a job into areas where a torch can be used safely and areas where it cannot. In the open field of a roof, on a well-sealed deck with no gaps, the flame is easier to control. Close to walls, in eaves, around pipes and at junctions with timber, the risk rises sharply. In these places the sheet is often fixed another way, such as a cold adhesive or a hot-air tool rather than a naked flame.

Good practice includes keeping the flame away from the sheet's edge, never heating directly onto timber, and having a fire extinguisher at hand on the roof. The roofer should also check the voids around the roof before starting, and keep watching the roof after the last flame goes out. Ask what they plan to do after laying, such as staying on site to look for heat or smoke, and how they will check the edges and penetrations.

It is fair to ask these questions when you are getting a quote. A confident roofer will explain the plan without fuss, and put it in writing. Questions like these are part of choosing a roofer; the same thinking runs through our page on flat roofing.

Where the setting is risky, a roofer can lay a covering that needs no flame. Cold-applied systems use an adhesive or a self-adhesive sheet. Liquid-applied membranes are rolled or sprayed on, and single-ply sheets such as EPDM, a synthetic rubber, are glued or fixed with plates and screws. GRP is laid in resin. Each has its own limits and each suits different roofs.

A cold system is a sensible choice on a roof with a thatch or timber-clad wall right beside it, an old, dry eaves void, an occupied building with sleeping accommodation directly below, or a tight site where the flame cannot be kept clear of anything that burns. Some insurers and landlords also set conditions on hot work, so it is worth asking before work starts. Our pages on liquid-applied flat roofing and EPDM roof lifespan describe two of the alternatives.

None of these is automatically better. A well-laid torch-on system is a proven covering, and a badly laid cold one can fail too. What counts is the match between the roof, the access and the method, and an installer who can tell you why they chose it.

Before you accept a quote, ask how the roofer will lay the covering and why. Ask which parts, if any, will be done with a flame, how the edges and penetrations will be treated, and what checks happen after the last torch is put away. Ask whether the roofer will be on site for a time afterwards, and whether the deck, eaves and any nearby timber have been looked at first.

Tell the roofer about anything unusual: a neighbouring thatch, a timber-clad wall, a lean-to against the house, or a sleeping loft directly beneath. These change the answer. Also check the roofer's plan for access and clearing the site each day, as loose rubbish and cylinders left on a roof are a risk in themselves.

On price, Checkatrade's September 2026 rubber roofing guide gives felt at £50 to £80 per m² as a national guide, and the figure for your own roof depends on the area, the layers and the access. The single written price follows the survey, once the edges and eaves have been looked at. More on how long a felt covering lasts is in how long a felt flat roof lasts.