Built-up roofing (BUR) and modified bitumen are two common flat roofing options, often chosen for their durability and water resistance. BUR is made from multiple layers of roofing felt or fabric embedded in asphalt or bitumen; the layers are alternated with hot asphalt to create a thick, strong membrane. This layered approach allows BUR to withstand harsh weather and foot traffic. Modified bitumen, on the other hand, is a more modern product featuring asphalt modified with polymers to improve flexibility and toughness. It usually comes in rolls and is installed via heat welding, cold adhesives, or self-adhesive sheets. The main difference lies in the installation method and material flexibility, with modified bitumen offering quicker application and better adaptability to temperature shifts and building movement.
To check which roofing type you have or which might be best for your home, look for a smooth or granular surface that feels thick and rubbery for modified bitumen, versus a built-up surface that appears layered and tar-like for BUR. You can also carefully observe roof flashings and seams—modified bitumen typically has visible roll seams, while BUR shows a more uniform, layered pattern. DIY inspections should focus on visible damage like cracks, blisters, or loose granules, but avoid walking on the roof if you’re uncertain of its strength. If you notice persistent leaks, large blisters, or damaged layers, it’s time to call a professional. When consulting a roofer, ask if your roof's warranty covers repairs specific to the type of membrane, and how the contractor plans to address potential heat damage during installation or repair, especially for BUR roofs. These questions help ensure that repairs maintain the roof’s integrity and warranty coverage.