
Built-up roofing consists of two or three layers of bitumen sheet bonded together through adhesive or hot bitumen.The bitumen is produced through the distillation of crude oil.
Reinforced bitumen sheets are manufactured using a base layer consisting of one of a number of materials including organic fibres, glass fibre or bitumen-saturated polyester, though in practice, organic felts rarely meet performance criteria.
The material is passed through a bath of molten bitumen and then coated with sand to prevent adhesion.