Introduced to the U.S. in the mid 1970s, modified bitumen membranes are roofing sheets made of asphalt that has been modified with either rubber (SBS) or plastic (APP) to offer greater stretch and flexibility. Similar to BUR, modified bitumen is installed in multiple plies, typically 2-3. Torches are used to join material body and seams, creating a watertight system. Modified bitumen can also serve as the cap sheet of a BUR roofing system. (This is commonly referred to as a “hybrid” roof system.)
One of the biggest drawbacks to modified bitumen is that extreme heat is needed to properly weld sheet seams, unless using cold-process adhesives. Heat is typically applied with open-flame torches, but if not used properly, these flames can start fires on the roof and in the underlying structure.
One reason why modified bitumen is one of the most popular roofing systems is how easy and quick the installation process can be for an experienced production crew. A quicker roof installation often times results in reduced labor costs, potentially saving you thousands on your new roofing system.
Modified bitumen is an excellent commercial roofing system because it is resistant to heavy foot traffic, punctures, and tears. Featuring plastic- or rubber-based polymeric binders in its formulation, modified bitumen is flexible and expands or contracts with the building, making it suitable for many different climates.
Modified bitumen sheets are manufactured under tight quality control, resulting in consistent thickness. Manufacturers assemble the torch-preparation linings, waterproofing binder, weather-resistant surfacing, and fabric reinforcement into sheets with uniform physical properties and thickness. This consistency guarantees a reliable and proven performance from the product.