Modified bitumen is a catch-all term that describes traditional flat roofing material such as SBS and APP.  It typically comes in rolls that cover 100 square feet each. A standard modified bitumen roof system is a two-ply system in which each sheet overlaps the edge of the previous one as you install from the low point to the high point of your roof. Mod-bit roofs are durable, cost effective, and easy to repair. They can be applied in cold adhesive, hot adhesive, torch applied, and self-adhered.