Bitumen membranes are still the undisputed front runner on domestic roofs. They are almost something of a traditional commodity. They not only have advantages. What types of bituminous membranes are there, what they serve, where to get them, and what they cost you can read in this article. Bitumen membranes: glued, welded or nailed As a rule, at least two layers of bitumen are always laid for roofing.