Built-Up Roofing membranes referred to by the acronym BUR, have been in use in the U.S. for more than 100 years. Built-Up roof systems are constructed with layers of felt and bitumen (either asphalt or coal tar pitch) that are applied hot and left to cool. They are then covered with gravel, a mineral sheet cap, or other weather resistant coatings. Generally, BUR systems are three or four ply. The layering of the bitumen and felt provide enhanced water resistance. These Built-Up Roofing systems are commonly referred to as “tar and gravel” roofs. Built-Up Roofing systems generally are composed of alternating layers of bitumen and reinforcing fabrics that create a finished membrane. 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. Sometimes, a base sheet, used as the bottom most ply, is mechanically fastened. Built up roofs generally are considered to fully adhere if applied directly to roof decks or insulation.
The reinforcing fabrics also 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 36 inches and metric width of about one meter.
The bitumen typically used in Built-Up Roofing BUR roof 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’s for built-up roofing 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. A Built-Up Roofing system composed of a built up roof membrane with two or three plies and a polymer-modified bitumen membrane cap sheet is commonly referred to as “hybrid” system. NRCA considers this type to be a polymer modified bitumen membrane system. Click HERE for more information about the GAF BUR roofing system.
Alpine Roofing Construction with 17 years of commercial roofing experience in all aspects of commercial roofing install maintains, repair and re-roof Built-Up Roofing Systems. We have experience working on properties from a small commercial retail property to a high rise building. No job is too big or too small. Contact Alpine Roofing Construction today for a free roofing consultation.