For over 100 years, Built up roof membranes have been in use in the United States. The Built
up roof system in most cases must be fully hot-mopped (broomed or squeegeed) to ensure
there are no voids between plies which can become blisters. The BUR systems are comprised
of alternating layers of bitumen and reinforcing fabrics. The term “3 plies” refers to the number
of plies in a cross section. The reinforcing fabrics are also called roofing felts. They are
reinforced with either glass-fiber mats or organic mats.
The surface for Built up roof systems usually include gravel. These roofing systems are
commonly referred to as “Tar and Gravel”
