Felt roofs consist of three layers of sheet felt materials that form a dense voidless and impermeable barrier.
Roofing felt is a composite of an absorbent sheet of organic or synthetic fibre that is impregnated / saturated and coated with a water-proofing agent such as tar or asphaltic bitumen to prevent ingress of moisture. Materials technology and new products have modernised the range of felts that many manufacturers supply. Modern man-made and composite materials felt roofs that use modified bitumen include rubber modified elastomeric bitumen and polytar modified bitumen are now available.
The felt roof system is build up of multiple layers of high performance felts and mastic asphalt over an insulated timber or concrete flat roof deck. When applied, the layers of vapour dispersion and control membranes are sealed with graded roofing felts to guarantee a waterproof installation. There are several techniques for applying felts depending on the materials used, however, felt is generally rolled out over the roof and bounded together by ways of hot bitumen.