What a felt roof is made from
A felt roof is built up from layers of bitumen-based sheet material, usually laid over timber decking. Depending on the system, the build-up might include an underlay or vapour layer, one or more intermediate layers, and a top, weatherproof cap sheet that gives the roof its finish, often with mineral granules bonded to the surface for protection from sunlight.
Torch-on felt: how it is applied
Torch-on felt is heated with a gas torch as it is unrolled, which melts the bitumen on the underside so it bonds to the layer beneath. Done correctly it gives a well-sealed roof, but working with an open flame close to timber decking, insulation and other combustible materials carries a genuine fire risk, and roofs have been damaged or lost during installation when heat has reached hidden timbers or built up in confined spaces.
Open-flame roofing requires appropriate fire precautions and competent installation. Do not attempt it yourself; the method described here is general information rather than a confirmed installation offering.
Cold-applied and self-adhesive alternatives
Cold-applied felt systems bond using adhesive or a self-adhesive backing rather than a flame, which removes the fire risk associated with torching. These systems have become more common on smaller or more sensitive roofs, such as those close to timber structures, overhangs or other buildings, where an open flame would be harder to manage safely.
Cold-applied systems are not automatically better or worse than torch-on felt in every situation; each has circumstances where it is the more practical or appropriate choice, and the right one depends on the roof, its surroundings and the layers specified. We would avoid ranking one as simply superior without looking at the specific job.
Signs a felt roof needs attention
Felt roofs show wear in fairly recognisable ways. Look out for blistering or bubbling in the surface, cracking or splitting where the felt has dried out and lost flexibility, lifted or curling edges at laps and upstands, gravel or mineral granules washing into the gutters, and ponding water that sits for more than a day or two after rain. Inside, damp patches or staining on a ceiling or garage roof boards are often the first sign that something above needs looking at.
Where the damage is limited to one area and the rest of the felt is sound, a localised repair can be a reasonable option. Where cracking or lifting shows up across the whole roof, or the deck underneath has started to soften, repeated patching tends to become uneconomic and a full replacement is usually the more sensible route. Our flat roof repairs page covers how repairs are assessed.
What affects the cost of a felt roof
The cost of replacing a felt roof depends on the size of the roof, the number of layers specified, the condition of the deck underneath, how many upstands, outlets and roof lights need detailing, and access to the property. A simple rectangular garage roof with one gutter is a more straightforward job than a roof tucked between walls with several junctions to seal.
Our guide to flat roof replacement cost sets out these factors in more depth, including how the choice between felt and alternative coverings such as GRP or EPDM can change the picture. The main flat roofing page compares those systems directly.
Felt alongside other flat roof systems
Felt remains a recognised and widely used flat roofing material, particularly for smaller structures and repair work, but it sits alongside other systems such as GRP fibreglass and EPDM rubber, which are built up differently and have their own strengths. There is no single covering that is automatically right for every roof, so the starting point for any decision should be an assessment of the existing roof and what it needs, not the covering alone.
For a specific felt roof enquiry, request a free site visit and written quote, describing leaks, the roof location and any previous patches. Stay off the surface and do not test a suspect deck by walking over it.