Modified bitumen roofing is a popular roofing material for flat roofs in Houston. It is especially common on commercial roofs. Modified bitumen roofing is an evolved version of asphalt built up roofing. It has a better seal than traditional asphalt roofing and it usually comes in self-adhering forms that require no heat for sealing. It is made of combination of asphalt and a polymer giving it the best of both worlds.