Built-up roofing, also known as BUR, is one of the most commonly utilized roofing systems for flat roof commercial buildings. BUR is a roofing method that has been in use for well over a century, and it provides excellent waterproofing protection due to the use of coal tar and bitumen.
A built-up roofing system is typically constructed of alternating layers of reinforcing material and bitumen, covered with a finishing layer of aggregate material, such as gravel or small stones.
First, a base sheet is fastened to the roof’s insulation or cover board. A layer of bitumen is then applied to the base sheet which binds with the next layer of reinforcing felt, also referred to as a ply sheet. Ply sheets are heavy-duty reinforcing fabrics strengthened with either organic material or fiberglass. Multiple coatings of bitumen and felt are applied, and after the desired number of layers have been placed, a mineral-reinforced cap sheet or aggregate material is used for the top layer. There are three main types of BUR systems: