Modified bitumen was developed in Europe in the 1960s and has been used as a roofing system in the United States since the mid 1970s. Combining asphalt with modifiers to give it either plastic (APP) or rubber (SBS) qualities, manufacturers sought to combine the durability and weathering capabilities of built-up roofing systems with the consistent manufactured quality and flexibility offered by single-ply.
Manufactured in rolls, modified bitumen can be applied in a variety of methods. Commonly, modified bitumen installers use adhesive-backed (self-adhered) sheets, cold process adhesives, hot asphalt, mechanical screws and plates, or torches to secure the modified bitumen to the substrate. It’s always good advice to check the manufacturer’s latest specifications on any installation. Proper application of the seams is critical. Some of the application methods require additional attention to the side laps and head laps after the sheets are installed.