Below are some of the most popular flat roofing systems, as well as a few benefits and drawbacks of each.
Diagram of Built Up Roof, from Owens Corning
Built Up Roofing (BUR)
Built up roofing is a generic term for a roof system that is literally built by adding layers. Built up roofing is most often made from alternating layers of roofing felt with different waterproofing materials, including coal tar pitch, asphalt, cold application adhesive, and modified asphalt. It is also known as “tar and gravel” roofing, because it’s finished off with a final layer of gravel, crushed rock, or other mineral substance, in order to minimize sun damage.
The other popular built up roofing style is a modified bitumen roof. MBR’s are made from fiberglass-based asphalt sheeting, applied in layers with mopped-on hot bitumen between each.
Built-up roofing is more commonly found on commercial buildings than on residential homes, but it’s still well suited for houses with flat roofs. While built-up roofing is the most economical choice of flat roofing, sunlight will eventually break down the asphalt base and the roof will need to be replaced sooner than other options.
Single-Ply Roofs
Single-ply roofs are the most reliable, popular, and practical flat roof solutions on the market. It comes in two main types. Thermoset membranes are manufactured from rubber polymers, and require the use of liquid adhesive or tape to form a watertight seal at the overlaps. Thermoplastic membranes, made from plastic polymers, have seams formed with heat or chemical welding. Most thermoplastic membranes include a reinforcement layer of polyester or fiberglass for increased strength and stability, as well.
Either way, these single ply roof materials, more commonly referred to as rubber or plastic roofing membranes, are probably the best choice if you need to replace flat roofing. They’ll cost a little more than built up roofing for materials and installation, but they will last a lot longer with far fewer problems. Any extra initial costs are well worth it in the long run.