Flat roofing
Torch-on felt roofing
The system most often specified for larger and more complicated flat roofs: layers of bituminous membrane bonded together with a gas torch, built up over a primed deck.
How a torch-on roof is built
- The deck is checked and any soft or damaged boards replaced. Nothing goes over a deck that has been getting wet.
- A vapour control layer and insulation are laid where the roof is being built as a warm deck.
- An underlay is bonded down, then a cap sheet is torched over it, with laps staggered so no joint sits above another.
- Upstands, outlets, drip edges and any penetrations are detailed with separate pieces, which is where the work either lasts or does not.
- The finished surface is mineral-faced, which protects the bitumen from ultraviolet light.
Where it suits
Larger areas, roofs with several penetrations or awkward junctions, and roofs where the shape means a single-sheet system would need a lot of joints anyway. It is repairable in a way that a fully seamless system is not: a damaged area can be cut out and a new patch bonded in.
What to watch
It is applied with an open flame next to timber and, often, next to a neighbour’s wall. That means competent operatives, the right heat-protection at abutments, and a proper watch period after the torches go off. Anyone quoting for torch-on work should be able to tell you how they handle that without being asked.
We use IKO systems for torch-on work. The manufacturer matters less than the detailing, but a full system from one manufacturer is what makes a materials guarantee mean anything.
Torch-on questions
Is torch-on felt the same as the felt roofs that used to fail?
No. The bitumen felt of the 1970s was a single layer of organic-based material that went brittle. Modern torch-on uses polyester or glass-reinforced modified bitumen in two or three bonded layers, which behaves differently under heat and movement. The name has stuck; the material has not stayed the same.
Can torch-on be laid over an existing felt roof?
Sometimes, if the existing covering is sound, dry and well bonded. Often it should not be: overlaying traps moisture in the old layers and hides whatever is happening to the deck. We will say which applies after looking, and we will not overlay to save a day if the deck needs seeing.
Not sure what your roof needs?
An inspection ends with a written report and photographs, whether or not you go ahead with the work.
Inspection fee: £99.00.