Felt roofs consist of two or three layers of sheet felt materials that form a dense impermeable barrier.
Roofing felt is a composite of an absorbent sheet of organic or synthetic fibre that is impregnated/saturated and coated with a waterproofing agent such as tar or asphaltic bitumen that prevents ingress of moisture.
The felt roof system is built 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 felt – depending on the materials used, however felt is generally rolled out over the roof and bonded together by way of hot bitumen or adhesives.
Materials technology and new products have modernised the range of felts many manufacturers supply, so modern man-made and composite materials felt roofs that use modified bitumen; include rubber modified elastomeric bitumen and polymer modified bitumen are now available.