Flat Roofing Styles

Built-up Roofs (BURs)

• The built-up roof, also known as a BUR or a "tar and gravel" roof, has been used for over 100 years. It remains the most economical flat roof style. This roof consists of alternating layers of bitumen and reinforced fabrics. The bitumen may be asphalt, coal tar or a cold-applied adhesive. The roof surface may be coated with aggregate material, such as gravel or mineral granules. Aggregate coatings serve to retard fires. However, they can also clog drain spouts. Other surfaces include a top sheet of fiberglass or mineral surfacing, or a coating of hot asphalt, aluminum or elastomere. All kinds of built-up roofs are relatively heavy, requiring reinforced joists, and are messy and smelly to install.

Polymer-modified Bitumen Sheet Membranes

• Polymer-modified bitumen sheet membranes, or MB membranes, have been used since the 1960s. Like BURs, polymer-modified membranes consist of several layers, with reinforced fabrics alternating between sheets of hot polymer-modified bitumen. Essentially, the polymer-modification changes asphalt into a rubber-like or a plastic-like substance, depending on the precise method used. For this reason, MB roofs are sometimes called "rubber roofs." Top layers may include aggregate, mineral, metal foil-laminate or smooth liquid-applied surfacings. The roofing may be applied either with a torch (not recommended near exposed wood porches) or through a peel-and-stick application. Pricing is mid-range, and the light-colored surfacing can prove energy efficient.

Ethylene Propylene Diene Monomer (EPDM)

• For a real rubber roof, use EPDM (ethylene propylene diene monomer). This roofing material resembles an inner tube, but can withstand continuous sun exposure. Made of synthetic rubber, EPDM roofs offer a nearly "seamless" solution to roofing, with strips of the material fusing together. The tough material resists tearing, and any tears are easy to patch, combating leakage problems. Protective UV coating keeps EPDM from degrading over time as asphalt could. The roofing can be affixed with anchors, ballasted with aggregate or glued down. As EPDM roofs are typically black, they absorb heat energy, making them inefficient in hot climates, but ideal for cold winters.