Modified bitumen roofing is a single-ply, tar based product. It was created as a replacement for built-up or “tar and gravel” roofing. Instead of installing numerous layers of roofing material as with built-up, modified bitumen is a complete roofing system in a single roll. The best way to describe modified roofing is to compare it to composition house shingles. Its composition is similar to a very thin house shingle that is in a large continuous roll.
Modified bitumen comes in granulated and non-granulated types. Of these types, the granulated in a light color is best in the south. Modified is installed one of two ways: peel and stick or torch down. The advantage of the peel and stick modified is the speed at which it can be installed, however, it does not always adhere well. The other method of installation is called torch down because the bottom tar side of the modified roofing is heated up with an open flame torch. The tar is melted, and the melted tar adheres the modified to the roof surface (which is normally some type of insulation or other substrate material). The biggest disadvantage to this type of modified is the danger of catching the roof on fire. Many structures have been lost by fire due to the torch catching the area below the roof surface on fire.