Polymer modified bitumus roofing is growing in use as the various methods are tested and observed over time.

Rhynehart Roofing, Inc. mainly uses Tamko products for this type of roofing system. This type of roofing is essentially a single-ply system. However, various mopped bitumus and roofing felt layers may be incorporated into the system at the installation. In re-roofing situations a viscous glue maybe sprayed or mopped over an old gravel surfacing before the Poly-membrane is attached. The glue adheres the old tar and gravel, levels the surface, and holds the Poly-membrane onto the roof. The Poly-membrane system started in Europe and has been in use in the U.S. since 1975. The modifying compounds, such as styrene-butadiene or atactic polypropylene, impart flexibility and elasticity, and improve cohesive strength, resistance to flow at high temperatures and toughness. Reinforcing materials consist of plastic film, polyester mat, glass fibers, felt or fabric; they may be embedded within or laminated to the surface of the modified bitumen sheet. Modified bitumen sheets may be self-adhered, or may be installed with hot asphalt or by heating the membrane with a propane torch. The seals are sealed by torch-welding or by using hot asphalt. The membrane may be surfaced with liquid coatings, metallic laminates, or ceramic or mineral granules to enhance ultraviolet resistance and fire resistance. Modified bitumen membranes range in thickness from 40 to 160 mils.

Built-up roofing is a continuous, semi-flexible multi-ply roof membrane, consisting of plies or layers of saturated felts, coated felts, fabrics, or mats between which alternate layers of bitumen are applied. Generally, built-up roof membranes are surfaced with mineral aggregate and bitumen, a liquid-applied coating, or a granule-surfaced cap sheet (NRCA Roofing and Waterproofing Manual-Fourth Edition)