Mop Down Roofing
Asphalt built up is the most common form of roofing used for low sloped roofs (2:12) in America, constituting a large percentage of the overall number of roofs in the United States. Asphalt built up refers to several layers of reinforcing felt between asphalt and plies, or coal tar bitumen, which are covered with a surfacing material that serves as a ballast and holds them down, also reflecting UV rays.
Usually the surfacing material used is gravel, and for this reason it is sometimes also called tar and gravel roofing. There are, however, other kinds of built up roofs, including smooth Asphalt built up, and Ballasted Asphalt built up. Depending on weather conditions, the average life span of asphalt built up roofs is approximately 10-20 years.