An economical choice common in areas with little or no rain, a flat roof, or a low slope roof, must be covered with a waterproof material and rely on a good drain system as water will not run off easily as it does with pitched roofs. Built-Up Roofing (BUR)
Built-up roofing is a generic term for a roof system that is literally built by adding layers. Built-up roofs are more commonly found on commercial buildings than homes, but they're well-suited to houses with flat roofs.
Built-up roofs are sometimes made from alternating layers of roofing felt with different waterproofing materials including coal tar pitch, asphalt, cold application adhesive or modified asphalt.
Built-up roofing is also frequently known as "tar and gravel" because it is finished with a layer of gravel, crushed rock or other mineral substance to minimize sun damage.
Modified bitumen roofs are made from fiberglass-based asphalt sheeting, applied in layers with mopped-on hot bitumen between each.
Single-Ply Roofing
Single-ply roofing systems come in two main types.
Thermoset membranes, compounded from rubber polymers, require the use of liquid adhesive or tape to form a watertight seal at the overlaps.
Thermoplastic membranes based on 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.
Both built-up and single-ply roofs generally have low maintenance costs over the life of the system. Material warranties are available for up to 12 years. However, these roofs must be removed and replaced after their usable lives.
Sprayed Polyurethane Foam (SPF)
Sprayed polyurethane foam (SPF) is sprayed onto the roof as a liquid to form a single continuous seamless structure. Because foam is flexible and lightweight it can be sprayed on irregularly shaped roofs and protrusions.
For reroofing, SPF eliminates the need for tear-off as it can be applied directly over existing roof installations, including asphalt, shingles, built-up roofs, clay tile, concrete, metal and wood.
With a high insulation value, foam roofing systems are easy to maintain. In fact, repairing and recoating an SPF roof could enable it to last indefinitely.
