Modified bitumen is a type of asphalt product that can be applied in a number of ways to the roof in both hot and cold temperatures. Modified bitumen roofs have a lot of advantages over other types of membrane roofing, and are often seen as the modern alternative to the built up roof. Bitumen roofs are one of the longer lasting types of flat roofing materials, easily lasting 20 years or more. Regardless of how the material is applied (self-adhesive sheets, hot-mopped asphalt, or cold-applied adhesives) the seams are usually melted together which help stop leaks. Other types of membrane roofing have seams that are left open or covered with another material that can weaken over time, so the fact that a bitumen roof can be seamless is a big advantage.
Bitumen roof is also very durable. They have a high-tensile strength so they are unlikely to develop the kinds of cracks that other flat and membrane roofs are known for. They are also rated against wind, fire, and hail so they are unlikely to be damaged in the event of a storm.
The key to getting a successful bitumen roof job done is to make sure you are having it done correctly. This means using a 2 or 3-ply material and having it coated against UV exposure. When done right, a bitumen roof can far outlast the competition.