Bituminous felt is waterproof sheeting used for surfacing roofs or as an underlay beneath tiles or slates.
Bituminous or Bitumen Felt is made from bitumen, a tar-like substance derived during distillation of crude oil, mixed with sand or crushed limestone, and applied to a fibrous membrane made from such materials as hessian, fibre-glass, polyester or paper. The felt may be finished with a coating of sand or fine gravel to give a decorative finish.
Bituminous felt is a cost-effective and convenient way of providing waterproof covering to roofs. It is widely used on flat roofs, as well as on sheds and similar garden buildings.
When used for surfacing flat roofs, the strips of felt have to be joined and finished in such a way that water cannot penetrate. This may be done with a gas torch (products suitable for this purpose are known as ‘torch-on’), or using an adhesive applied cold.
Bituminous felt on a flat roof should have a long life if properly applied, but is prone to damage and does decay over time. A survey report should therefore comment on the condition of any flat roof, especially if there is evidence of water penetration.