Built-Up Roofings have been in use in the U.S. for more than 100 years. Built-Up Roofing consist of multiple layers of felts, fabrics or mats that are saturated with bitumen – either asphalt or coal tar pitch. The number of plies in a cross section is the number of plies on a roof: The term “four plies” denotes a four ply roof membrane construction. Built-Up Roofings generally are considered to be fully adhered if applied directly to roof decks or insulation.
The bitumen typically used in Built-Up Roofing 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.