What Is Modified Bitumen Roofing?
Modified bitumen roofing is an advanced evolution of traditional built-up roofing technology. Developed in Europe in the 1960s and introduced to the United States in the 1970s, modified bitumen combines the time-tested waterproofing properties of asphalt with modern polymer modifiers that significantly enhance the membrane's flexibility, durability, and weather resistance. The result is a robust, multi-layer roofing system that offers the reliability of BUR with improved performance characteristics suited to modern commercial building demands.
Modified bitumen membranes are factory-manufactured in rolls, with the polymer-modified asphalt compound reinforced by a strong polyester or fiberglass mat. This controlled manufacturing process ensures consistent thickness, uniform modifier distribution, and reliable quality that cannot always be achieved with field-built roofing assemblies. The rolls are then installed on the roof using one of several application methods, creating a seamless, waterproof membrane that protects the building for decades.
APP vs. SBS: Understanding the Two Types
Modified bitumen roofing is available in two primary formulations, each engineered with a different polymer modifier to achieve specific performance characteristics. Understanding the differences between these two types is essential for selecting the right system for your building.
APP (Atactic Polypropylene) Modified Bitumen
APP-modified bitumen uses a plastic-based polymer that gives the membrane excellent UV resistance and heat stability. APP membranes have a higher softening point than SBS products, making them well-suited for buildings in warm climates or those with rooftop areas exposed to intense solar radiation. The plastic modifier creates a smooth, uniform surface that sheds water efficiently and resists degradation from prolonged UV exposure without the need for additional protective coatings.
APP-modified bitumen is almost exclusively installed using the torch-applied method, where the underside of the membrane is heated with an open-flame propane torch as it is unrolled across the roof surface. The heat melts the bitumen, which then bonds the membrane to the substrate and adjacent sheets as it cools and solidifies. Torch application creates strong, reliable bonds between layers and produces a fully waterproof membrane assembly.
SBS (Styrene-Butadiene-Styrene) Modified Bitumen
SBS-modified bitumen uses a synthetic rubber polymer that imparts outstanding flexibility and elongation properties to the membrane. SBS membranes can stretch up to 800 percent of their original length without tearing, which provides exceptional resistance to the thermal movement and structural settling that all commercial buildings experience over time. This rubber-like flexibility is particularly valuable in cold climates where roofing membranes are subjected to extreme contraction forces during winter months.
SBS membranes offer the greatest versatility in installation methods. They can be torch-applied like APP products, or they can be installed using cold-applied adhesives or as self-adhered sheets with factory-applied adhesive backing. This flexibility in application methods makes SBS the preferred choice for buildings where open-flame work is restricted, such as occupied buildings, healthcare facilities, or structures with combustible substrates. For commercial buildings in the Chicago area and throughout the Midwest, SBS-modified bitumen is frequently the recommended choice due to its superior cold-weather performance.
Installation Methods
One of modified bitumen's key advantages is the range of installation methods available, allowing contractors and building owners to select the approach best suited to the project's specific requirements and safety considerations.
Torch-Applied Installation
Torch application is the traditional installation method for modified bitumen and produces the strongest bond between membrane layers and the substrate. Experienced installers use propane-powered torches to heat the underside of the membrane roll as it is carefully unrolled across the roof surface. The heated bitumen on the underside of the sheet liquefies, creating a full-surface bond as it cools. Windward Roofing's torch-applied installers are thoroughly trained in fire safety protocols and hold active hot-work certifications. We maintain strict fire-watch procedures on every torch-applied project to ensure the safety of the building, its occupants, and our installation crews.
Cold-Applied Installation
Cold-applied modified bitumen systems use specialized adhesives to bond the membrane sheets to the substrate and to each other without the use of open flame or heat. The adhesive is applied to the substrate using rollers or spray equipment, and the membrane sheets are rolled into the wet adhesive and pressed into full contact. Cold-applied installation eliminates the fire risks associated with torch application, making it the preferred method for occupied buildings, hospitals, schools, and other facilities where open flame work poses unacceptable risks. Cold-applied adhesives have improved significantly in recent years, providing bond strengths that approach those achieved with torch application.
Self-Adhered Installation
Self-adhered modified bitumen membranes feature a factory-applied adhesive layer protected by a removable release film. During installation, the release film is peeled away and the membrane is positioned and pressed onto the prepared substrate. Self-adhered systems offer the fastest installation speed and eliminate both open flame and solvent-based adhesive vapors from the job site. These systems are particularly well-suited for projects with tight schedules, sensitive indoor environments, or occupied buildings where minimizing disruption is a priority.
Benefits of Modified Bitumen Roofing
Exceptional Flexibility and Elongation
Modified bitumen membranes, particularly SBS-modified products, offer outstanding flexibility that allows the membrane to accommodate building movement, thermal expansion and contraction, and minor structural settling without cracking or splitting. This flexibility is critical in the Midwest climate, where temperature swings of 100 degrees or more between summer and winter place enormous stress on roofing materials. Modified bitumen's ability to flex with these temperature changes helps maintain waterproof integrity throughout all seasons.
Multi-Layer Redundancy
Modified bitumen roofing systems are typically installed as multi-ply assemblies consisting of a base sheet, one or more interply sheets, and a cap sheet. This multi-layer construction provides built-in redundancy similar to traditional built-up roofing. If the top layer is damaged by foot traffic, hail, or debris, the underlying layers continue to provide waterproof protection while repairs are arranged. This redundancy gives building owners peace of mind and reduces the urgency of emergency repairs.
Superior Foot Traffic and Puncture Resistance
The thick, reinforced construction of modified bitumen membranes provides excellent resistance to foot traffic, dropped tools, and mechanical damage. Granule-surfaced cap sheets add an additional layer of protection against abrasion and wear. This durability makes modified bitumen an excellent choice for buildings with rooftop equipment that requires regular maintenance access, including HVAC units, satellite systems, and telecommunications equipment.
Proven Waterproofing Performance
Modified bitumen membranes are essentially asphalt-based, and asphalt is one of the most effective waterproofing materials known. The polymer modifiers enhance this natural waterproofing capability while adding the flexibility and durability needed for long-term performance. When installed in multi-layer configurations with proper lap sealing and flashing details, modified bitumen systems provide outstanding waterproofing protection for the life of the roof.
Modified Bitumen Repair Services
Windward Roofing provides responsive repair services for all types of modified bitumen roofing systems. Common repairs include patching membrane splits and punctures, resealing open seams, replacing damaged flashing components, and addressing blistering or ridging in the membrane surface. Our crews carry the tools and materials needed for both torch-applied and cold-applied repairs, ensuring compatibility with your existing roof system.
We also provide proactive maintenance programs that include regular inspections, debris removal, drain cleaning, and documentation of roof conditions. Catching problems early through routine inspection is the most cost-effective way to extend the service life of a modified bitumen roof and avoid the disruption and expense of emergency repairs.
Why Choose Windward Roofing for Modified Bitumen?
Windward Roofing and Construction has been installing and servicing modified bitumen roofing systems since 1984. Our crews are experienced in all three installation methods and are fully trained in the fire safety protocols required for torch-applied work. We work with premium products from leading manufacturers including Sika, Johns Manville, GAF, and Tremco, and we maintain the certifications needed to offer comprehensive manufacturer warranty programs.
With projects spanning Illinois, Wisconsin, Michigan, Indiana, and Florida, we understand the unique demands that different climates place on modified bitumen roofing systems. Our team evaluates every project individually to recommend the optimal membrane type, number of plies, and installation method based on the building's specific requirements, local code compliance, and budget considerations. From new installations to complex re-roofing projects, Windward delivers the expertise and quality workmanship that commercial building owners depend on. Contact us today to discuss your modified bitumen roofing project.
Frequently Asked Questions About Modified Bitumen Roofing
APP (Atactic Polypropylene) modified bitumen uses a plastic-based modifier that provides excellent UV resistance and is typically torch-applied. SBS (Styrene-Butadiene-Styrene) modified bitumen uses a rubber-based modifier that provides superior flexibility in cold temperatures and can be installed using torch, cold-adhesive, or self-adhered methods. SBS is generally preferred in cold climates like Chicago.
Modified bitumen roofing systems typically last 20 to 30 years when properly installed and maintained. The actual lifespan depends on the specific product, number of ply layers, installation method, climate exposure, and maintenance practices. Regular inspections and prompt repairs help maximize service life.
When installed by trained, experienced professionals like Windward Roofing's crews, torch-applied modified bitumen is safe and effective. Our installers hold fire safety certifications and follow strict hot-work protocols including fire watches and proper equipment procedures. We also offer cold-applied and self-adhered alternatives for buildings where open flame is not permitted.
In many cases, modified bitumen can be installed as a recover over an existing roof, provided the existing system is in suitable condition and local building codes permit additional roof layers. This approach reduces costs and project duration by eliminating tear-off. Windward Roofing evaluates each building to determine if a recover is appropriate.
Modified bitumen roofs benefit from semi-annual inspections, debris removal, drain cleaning, and prompt repair of any splits, blisters, or flashing issues. Windward Roofing offers maintenance programs that include comprehensive inspections, condition documentation, and priority repair services to protect your roofing investment.