Modified bitumen roofing systems
Roofing with modified bitumen (mod-bit) offers a variety of technologies and installation methods. With proven historical performance and time-tested durability, mod-bit roofing products are a go-to material of choice for high-end low-slope buildings.
Understanding modified bitumen roofing
As parts of the asphaltic family of roofing solutions, SBS & APP Modified Bitumen and BUR are among the oldest and most common roofing technologies in use today, providing a reliable solution for both residential and commercial properties. Commercial asphalt roofing systems consist of two or more waterproofing layers, offering redundancy for durable waterproofing protection.
Explore mod bit productsField-proven for decades, GAF Mod-Bit roofing provides durability and performance
Weather resistance and durability
Thanks to high-quality raw materials and rigorous quality control, GAF SBS and APP Mod Bit and BUR roofing solutions provide durability and weather resistance for the long haul.
Solar-reflective options
Make GAF SBS and APP mod-bit membranes part of your cool-roof solution.
Hybrid solutions
Hybrid systems can increase the overall robustness of the assembly by combining characteristics of multiple roofing technologies, such as SBS Mod Bit and TPO.
Competitive limited guarantees
GAF No-Dollar-Limit commercial limited guarantees up to 35 years are available for qualifying systems.
Sample GAF mod bit and BUR roof system assemblies
SBS (Styrene Butadiene Styrene)
SBS (Styrene Butadiene Styrene)-modified asphalt allows these membranes to achieve greater elongation ratings than other asphaltic systems. Can be hot-mopped, cold-applied, heat-welded, or self-adhered.
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APP (Atactic Polypropylene)
APP (Atactic Polypropylene)-modified asphalt helps the roofing membrane to achieve durability and protection against the damaging effects of UV rays and weather elements. Typically torch-applied.
BUR (Built-Up Roofing)
BUR involves melting bricks of asphalt and applying it between base, ply, and cap sheets with mops (hot mopping). Some jobs are finished with a layer of gravel overburden over the last layer of asphalt.
Browse BUR membranes
SBS, APP & BUR roof system product comparisons
SBS and APP are polymers with unique characteristics, and membranes made with them are classified by ASTM numbers, types and grades. BUR is an assembly method in which multiple layers of felts are installed with hot asphalt in-between.
Installation methods for mod bit roofing systems
Hot-Mopped
Blocks of asphalt are melted in a large kettle and spread on the roof with mops .This is one of the oldest asphalt roofing techniques, and still provides a durable, water-resistant seal today.
Heat-Welded/Torch-Applied
The installer melts the underside of the asphalt membrane using a torch. This allows the sheet to adhere to the substrate below.
Cold-Applied
The installer attaches the roofing membrane to the substrate or previously applied layer of roofing material with a liquid adhesive (e.g, Matrix 101) using a notched squeegee or applicator gun.
Self-Adhered
Self-adhered asphaltic membranes include a factory-installed adhesive, protected by a film backing. The membrane is rolled out, and the film backing gets peeled away to expose the adhesive.
Project profiles: GAF asphaltic roofing systems
Get inspired for your next Mod Bit roofing system project with these real-life GAF asphaltic profiles.
Frequently asked questions
The most common misconception about mod-bit roofing is that it can’t be part of a cool roof system solution. Modern granule technology, such as GAF EnergyCap™ granules in Bright White and Ultra Bright White provide CRRC-rated reflectance to your asphlat roofing system.
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.See the Commercial Roof Warranty Comparison Guide for details.
Like any roof, regular inspections and maintenance (patching leaks, clearing debris) can help extend the functional life of your mod bit roof. GAF provides a scheduled maintenance checklist containing some important maintenance tools and information to help you maximize your new roof’s performance — and guarantee its coverage — for many years to come.
Choosing the right roofing system depends on many factors, including (but not limited to) budget, size, building use, climate, and potential sustainability goals.