Built Up Roofing

This is the most common type of flat roof used in this day and age. These systems are commonly made by alternating layers of bitumen and reinforcing fabrics in order to construct a finished membrane. Since it is made up of multiple layers of reinforcing plies and asphalt this forms a redundancy of water proofing layers. Built up roofs generally are considered to be fully adhered if applied directly to roof decks or insulation.

The reinforcing fabrics are called roofing felts or ply sheets. Roofing felts are reinforced with either glass-fiber mats or organic mats. Felts are produced in a standard width of about one meter.

The bitumen typically used in Built Up Roofing systems is asphalt, coal tar or cold-applied adhesive. The asphalt or coal tar is heated in a kettle or tanker and then applied by mop or mechanical spreader. Asphalt is a petroleum product refined from crude oil; coal tar is derived from the distillation of coal. Cold-applied adhesives typically are solvent-based asphalts that don't have to be heated in a kettle or tanker.

Surfacing for built up roof systems include aggregate (such as gravel, slag or mineral granules), glass-fiber or mineral surfaced cap sheets, hot asphalt mopped over the entire surface, aluminum coatings or elastomeric coatings.

The reflectivity of built up roofs depends on the surfacing material used. Gravel is the most common and they are referred to as asphalt and gravel roofs. 

Regular maintenance is required to ensure that a BUR roofing system achieves its life expectancy.