Modified Bitumen Roofing
Multi Layer Low Slope Roofing Systems
SBS (Styrene Butadiene Styrene)
SBS was introduced in the 1970’s, and features asphalt that has been modified (thus the name, modified bitumen) with the polymeric material SBS. This synthetic rubber allows the SBS sheets to achieve a greater elongation rating than other asphaltic systems. SBS systems also have the widest range of application methods, such as, hot-mopped, cold-applied, heat-welded or self-adhered. An SBS system consists of two plies of roofing membrane. The first ply is a smooth-surfaced SBS base sheet, installed, over insulation or a cover board. Then the system is finished by applying a granulated cap sheet over the smooth base/ply sheet. SBS membranes are classified by ASTM numbers, types and grades:
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ASTM D6162: SBS sheet using a combination of both polyester and glass fiber
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ASTM D6163: SBS sheet using glass fiber reinforcement
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ASTM D6164: SBS sheet using polyester reinforcement
- ASTM D6162 and D6163 have three type classifications, Type I, Type II and Type III.
- ASTM D6164 has two type classifications, Type 1 and Type Typically, the higher the type, the larger the mass and physical properties.
There are two grades of SBS sheet:
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Grade S: The sheet has a smooth surface
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Grade G: The sheet has a granule surface
APP (Atactic Polypropylene)
APP was first introduced in Italy in 1965 and subsequently brought to the United States a decade later in 1975. APP features asphalt that has been modified (thus the name, modified bitumen) to include atactic polypropylene – a plastic that allows the roofing membrane to have durability as well as offering protection against the damaging effects of suns UV rays and other weather events. APP is typically only applied with a torch – a key difference from SBS. However, just like SBS systems, most APP systems will consist of two membranes, a smooth sheet and a granule cap sheet. APP sheets are typically installed over either a BUR (built up roof) base sheet or thermal barriers as many substrates cannot be directly torched to. APP sheets are also typically used to recover existing roof systems.
APP membranes are classified by ASTM numbers, types and grades.
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ASTM D6222 – APP sheet using polyester reinforcement
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ASTM D6223 – APP sheet using a combination of both polyester and glass fiber reinforcement
- ASTM D6222 and D6223 have two type classifications, Type I and Type II. Typically Type II will have a larger mass and higher physical properties than Type I.
There are two grades of APP sheet:
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Grade S: the sheet has a smooth surface
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Grade G: the sheet has a granule surface
