Withstanding the test of time, bituminous roofing products bring a proven track record to low-slope roofing. Bituminous roofing systems are known for their long service life, dependability, and exceptional waterproofing.
There are two main types of bituminous roof systems, built-up roofing (BUR) and multi-ply, polymer-modified bitumen. The two-main polymer-modified bitumen membranes on the market are SBS and APP membranes.
Built-Up Roofing (BUR)
BUR systems have been used for more than 100 years in the United States. BUR systems are composed of alternating layers of oxidized bitumen and bitumen-coated membranes, often called felts or ply sheets. Ply sheets are generally reinforced with a dimensionally stable, high tensile strength fiber glass mat. BUR systems are surfaced with an aggregate or roof coating to improve the weathering capability of the system, and the redundant, multi-ply approach ensures the system provides dependable waterproofing for many years.
Modified Bitumen (Modbit) Systems
Modbit systems consist of base plies and a cap sheet, sharing the main dependable waterproofing benefits of a BUR system. Modbit systems are high customizable. Cap sheets in modbit systems are surfaced with a mineral granule to increase the weatherability of the system, and cool roof granules and coatings can be used to reflect UV rays, increasing the long-term performance of the roof, and lowering energy costs for the building.
SBS membranes are constructed with bitumen that has been modified with elastic Styrene-Butadiene-Styrene (SBS) polymers to form a “rubberized” asphalt coating. The coating is applied to a reinforcing carrier of fiber glass for high tensile strength and dimensional stability, polyester for superior elongation and tear strength, or a composite of the two. SBS membranes offer excellent flexibility, especially in cold weather. SBS membranes can be self-adhering but are generally installed with mopping asphalt or cold adhesive.
APP membranes are constructed with bitumen that has been modified with plastic Atactic Polypropylene (APP) polymers, resulting in a coating with the highest temperature range and enhanced durability and toughness. The coating is usually applied to a polyester carrier mat, but a small amount of fiber glass products also exist. APP membranes are mainly torch-applied due to the meltability of the plasticized bitumen.