built up felt roofing

A built up felt roof is a proven method of waterproofing roofs, generally flat roofs, by using numerous layers of bituminous roofing felt, all of which is bonded to the previous layer. To protect the felt from the sun, it is usually laid with chippings or a mineral cap sheet as the top layer.

The felt itself is the waterproofing layer, providing a reliable, hard wearing layer of protection against moisture ingress. It comes on 1m wide rolls in various lengths, from 8-20 metres depending on manufacturer. The felt consists of a mat of fibres which are coated on both sides by a bituminous layer. The felt surface is finally coated with a light sand which prevents the felt from sticking to itself on the roll. 

There are a variety of felting materials on the market, the main differences lying in the fibre mats as well as the finished surface. Modern felts generally use either a glass fibre mat or a high performance polyester mat. The finished surfaces consist of either sand or slate granules for a mineral finish.