Mineral Felt flat roofs

Mineral felt has been around for quite some years

Green mineral felt

Three layer felt roof

Pour and Roll

So what is mineral felt

Mineral Felt

Mineral felt roofing is also known as:

  • Torch on flat roofing or Torch on felt.
  • Hot bitumen flat roof or Pour and Roll application. Hot mop.
  • Three layer felt or Built up three layer felt roof.

All of the above are ways of using this kind of product.

Torch on felt has predominantly taken the market over because of the ease of installation. The new high tensile, torch on felts that have taken over from the traditional mineral felt roofingsystems are now so good that some manufacturers are guaranteeing their products for 20 years. However it is very hard to get a company to guarantee the roof for this long and if you are looking to guarantee a flat roof for this length of time make sure that the guarantee is an insurance backed policy. If you want a flat roof with a good long lifespan, look at the new EPDM Rubber roofing.

Some of the advantages of torch on felt are:

  •  Available in a variety of colours
  • Easy to buy as most roofing suppliers stock some sort of torch on felt, however not always the best quality, high tensile, torch on felt.

Using torch on felt as repair material for old flat roofs and old felt flat roofs is where it has significant value. Once the area to be repaired is cleaned and dried, torch on felt can be applied to the area quickly, and will probably outlast the surrounding roof.

Ponding and torch on felt

What is ponding? This photo clearly illustrates ponding.

The roof hasn’t got a great enough fall to it, so rainwater rests on the surface. This is a particular problem with old felt roofs and indeed many new flat roofs, especially torch on felt flat roofs.


The problems caused are:

  • When the water freezes it expands and cracks the felt.
  • Over a period of time, as the weight of rainwater increases, it can create a significant dip in the roof surface. This can eventually split the felt.
  • It will seep into any open joint and drain down into the area below causing waterdamage.

The heat of the sun takes its toll on old felt flat roofs by melting them. Solar heat causes cycles of expansion and contraction which leads to cracking. The heat can be deflected in a few different ways by:

  • Adding a capping layer of solar-reflective mineral stones.
  • Laying a reflection torch on felt which incorporates mineral stones
  • Painting the roof with a solar-reflective paint, normally white or silver.

Normally this isn’t the case with new torch on felts as they tend to be very rubbery and resistant to the variable weather in this country.


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