Flat roofs, or more specifically roofs with a fall of less than 10 degrees, form a significant part of the commercial roofing market. There is a wide range of choices for the specifier and many compete head to head in terms of specification, cost and performance. The built-up, multilayer felt roof dates from the 1940s and uses several layers of bitumen-impregnated felt. It is a practical solution, being relatively cheap and long-lived, as well as being easy to repair and maintain. Today the basic bitumen sheet has been improved with the use of electrometric coatings and by interlacing the bitumen with a polymer weave. This gives it better movement properties and greater strength. It is usually installed as a three-layer system consisting of a base layer bonded to the substrate or insulation, an intermediate layer providing primary waterproofing and a top sheet that may have a decorative solar reflection and slip reduction coating. The top sheet can come in a number of colours. Variations include using electrometric mineral sheets in two-layer or even one-layer systems.
展开▼
