APP Modified Bitumen Membranes
APP-Modified Bitumen is asphalt base that has been modified with Atactic Polypropylene — a plastic polymer that allows the roofing membrane to achieve durability and protection against the damaging effects of UV rays and weather elements.
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Asphaltic Commercial Roofing 101
Proven historical performance. Time tested durability. Asphaltic roofing products are a go-to material of choice for high end low-slope buildings. Learn more about asphaltic technologies and application techniques, as well as how to decide if asphaltic is the right roofing solution for your next project.
Benefits of GAF APP Modified Bitumen membranes
UV-stabilized weather protection
Rigid, UV-stabilized weather protection that performs very well in climates with intense sunlight
Excellent puncture resistance
Torch application
Designed primarily for torch application
What’s the difference between SBS, APP, and BUR?
| Characteristics | APP Modified Bitumen (e.g., RUBEROID® APP) | SBS Modified Bitumen (e.g., RUBEROID® SBS) | Built-Up Roofing (e.g. GAFGLAS® BUR) |
| Weather Resistance | These membranes provide rigid, UV-stabilized weather protection and perform excellent in hot, sun-drenched climates. | These membranes act like synthetic rubber, exhibiting outstanding flexibility, allowing them to bend without breaking during extreme temperature drops (with service ranges as low as -20°F). | Provides maximum waterproof protection using alternating layers of asphalt roofing felt plies, typically capped with a high- performance BUR or SBS granulated cap membrane. |
| Durability | Designed primarily for torch-application, creating a monolithic, highly bonded roof surface that withstands weathering. | Excellent tear and puncture resistance. These systems are highly effective when applied using hot asphalt or cold-applied adhesives. | The multiple layers offer robust physical strength and superior resistance to heavy roof traffic. When capped with a reflective mineral surfacing (EnergyCapTM), BUR systems can efficiently resist long-term harmful UV degradation. |
How GAF APP Modified Bitumen Membranes are installed
GAF APP modified bitumen membranes can be installed using hot air welding or torches, offering contractors flexibility to match project conditions, building type, and warranty requirements. Torch-applied installation is common for APP membranes because the plastic-modified asphalt responds well to controlled heat, but other methods may be available depending on the specific product and system. Watch the video for an overview of installation practices used in GAF asphaltic roofing systems, including APP and SBS modified bitumen membranes.
Related APP Membranes blog articles
Asphaltic Roofing Systems: An Effective Choice for Commercial Properties
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Asphaltic roofing options like Styrene-Butadiene-Styrene (SBS), Atactic Polypropylene (APP), and Built-Up Roofing (BUR) deliver durable, cost-effective solutions for low-slope commercial roofs. This overview details the performance differences, UV capabilities, and installation methods of each asphalt-based material to help contractors select the right system for their projects.
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Atactic Polypropylene (APP) modified bitumen incorporates plasticizing polymers to deliver exceptional heat and UV resistance. Designed primarily for torch application, APP membranes create a tough, durable barrier that excels in hot climates and high-temperature environments.
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What Is SBS Roofing?
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Formed by modifying bitumen with a synthetic rubber polymer, SBS roofing provides enhanced cold-weather flexibility, impact resistance, and elongation. Its multi-layer construction easily handles heavy foot traffic and thermal expansion while supporting a variety of installation methods, including torch-applied, self-adhered, and cold-applied systems.
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What Is a Built Up Roof?
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Built-Up Roofing (BUR) is a time-tested, highly redundant system featuring alternating layers of reinforcing felt plies and asphalt topped with a protective cap sheet or aggregate flood coat. Designed for low-slope applications, BUR provides exceptional weather protection, long-term leak resistance, and optional reflective surfaces to improve energy efficiency.
October 7, 2020
APP Modified Bitumen roofing membrane FAQs
APP-Modified Bitumen is asphalt base that has been modified with Atactic Polypropylene — a plastic polymer that allows the roofing membrane to achieve durability and protection against the damaging effects of UV rays and weather elements. GAF APP membranes are typically applied with a torch APP cap sheets are typically installed over either an APP base layer, BUR base sheet or ply, or thermal barriers, as many substrates cannot be directly heat-welded to.
Atactic Polypropylene (APP) is a plastic polymer while Styrene-Butadiene-Styrene (SBS) is a synthetic rubber polymer. APP primarily invests asphalt with rigid, UV-stabilized weather protection. SBS primarily invests asphalt with elastic properties.
APP modified bitumen is typically applied as a single cap sheet over a complete roofing system, while BUR comprises alternating layers of asphalt roofing felt plies, typically capped with a high-performance BUR, APP, or SBS granulated cap membrane.
Durable and long-lasting, GAF mod-bit and BUR roofing systems are eligible for No Dollar Limit guarantees up to 35 years for qualifying systems, with a typical APP application guarantee ranging from 10-20 years. See the Commercial Roof Warranty Comparison Guide for details.
GAF APP-modified bitumen membranes are usually torch-applied. The installer melts the asphalt on the underside of the membrane with a torch or hot-air welder, allowing the sheet to adhere to the substrate below. Membrane-to-membrane application allows the polymers to crosslink, providing a chemical bond that is very difficult to break.
A wide range of building types can benefit from the features of an APP-modified asphaltic roofing system. In particular, roofs subject to intense heat and/or sunlight can be well served by the UV resistance of APP mod bit.
APP mod bit membrane provides excellent waterproofing protection for roofs that see very limited traffic or overburden, and is best suited for buildings uses that are amenable to potential temporary disruption caused by the smell of torch application.
Durable and long-lasting, GAF mod-bit and BUR roofing systems are eligible for No Dollar Limit guarantees up to 35 years for qualifying systems, with a typical APP application guarantee ranging from 10-20 years. See the Commercial Roof Warranty Comparison Guide for details.