Understanding the different asphaltic roofing products can help you better decide which materials to use on commercial projects. For instance, atactic polypropylene (APP), styrene butadiene styrene (SBS), and built-up roofing (BUR) membranes all help protect the roof and building from the outside elements.
APP roofing membranes are produced by adding specialized polymer to bitumen to create a modified bitumen material. This APP polymer increases the bitumen's ultraviolet (UV) resistance, impact resistance, flexibility, and durability, helping it withstand the elements. Here's what to know about APP roofing, when you might use it, and how to install it.
Advantages of APP-Modified Bitumen
APP roofing membranes offer several benefits to building owners and occupants alike.
Solar Reflectivity
APP roofing cap sheets offer some of the best protection against UV radiation. Granulated cap sheets surfaced with GAF's EnergyCap granules are constructed to reflect the sun's rays and help slow the aging process caused by continuous UV exposure.
Ben Runyan, Director Product Management, PVC and Modified Bitumen Systems for GAF describes APP as a more "rigid" and "forgiving" material for installers in high-heat environments. "They can put a little bit of extra heat to it... there's a little more room for error than there is with SBS where if you put heat to SBS too much, you'll burn the membrane up," he explains.
Longevity
APP-modified bitumen roofs' protective abilities also allow for a long lifespan. Since the sun is often the main culprit that degrades roofing materials, the granulated cap membrane layer helps to prevent this breakdown. The granule surfacing's durability coupled with the membrane multiply redundancy means the roof doesn't experience huge temperature changes that could cause it to expand and contract, forming cracks and potentially leak points.
Reduced Chance of Leaks
Since this roofing system requires sealed side and end laps, it has fewer vulnerable points for water to get through. Its exceptional protection, resistance to cracks, and seamless installation combine to create a roof with a significantly reduced chance of leaks. APP-modified bitumen is typically installed in multiple layers, including a base layer membrane and a cap membrane. This tiered structure ensures that even if one layer fails, the others still protect the substrate underneath. Other applications can include one layer of either base or cap then a liquid membrane coating such as a silicone or acrylic with an asphaltic bleed block primer installed prior to the coating application.
Flexibility
APP modified bitumen membranes are also flexible. While it may not be as flexible as SBS-modified bitumen, its properties still work similarly and efficiently across harsh weather conditions. The asphaltic polymer blend can shift during weather changes and handle foot traffic. If a building roof is expected to house heavy equipment like HVAC units or solar panels, its heavy foot traffic capabilities make it an ideal choice.
To explain the physical difference, Runyan uses a plastic vs. rubber band analogy: "APP is like the plastic—it holds its shape. It is a more rigid and durable product from a bendability standpoint, making it very effective for handling foot traffic."
Cost-Effective
While APP asphaltic roofing systems have some initial upfront costs, its durability means it can last a long time—making it cost-effective in the long run and bringing forth beneficial lifecycle cost of ownership to the building owner. Due to its sturdy construction, an APP roof also has low maintenance needs which can lead to more cost savings and less building interruption.
When to Use APP-Modified Bitumen
APP-modified bitumen roofs function well in warm and sunny climates. While it may not share the same elastic flexibility as SBS roofs, the bitumen blend still carries some level of long term membrane flexibility. APP also has enhanced UV resistance thanks to the APP polymer addition to its asphaltic blend.
Modified bitumen roofs are also commonly used for low-slope roofs. These roofs often deal with standing water since the runoff system isn't as quick due to its slope. The material's built-in water protection and seamless molecular bonding can help prevent leaks to enhance long-term system performance. With the multilayer construction brings the confidence that an APP system can handle some of the most challenging environmental conditions.
How to Install APP Roofing
APP-modified bitumen roofs are commonly installed using the torch-applied method. This involves melting the asphalt on the underside of the membrane with a torch so it strongly adheres to the roof substrate by a molecular bond.
The membrane you choose depends on the job and factors such as the location, environmental, and client preferences or project specific requirements.
Success in APP installation requires attention to detail. "The critical nuance is making sure they have burned off the burn-off film," Runyan notes. Contractors should also look for "bleed out" on the side and end laps to verify that the project is truly watertight.
Choosing the Right Membrane for Your Next Job
Understanding the different commercial roofing materials and installation methods is crucial for ensuring customer satisfaction. As a commercial contractor, you want to find the right solution for each situation. When using GAF products, you can rest assured you're providing your clients with quality roofing options that will provide years of protection. We recommend reaching out to your local GAF commercial sales representative to help guide you through the possibilities when choosing an asphaltic system.
Curious to learn more about SBS, APP, and BUR systems? Explore the GAF YouTube playlist Asphaltic Commercial Roofing 101 for detailed information about cutting-edge asphaltic products, system solutions and installation methods.
