Low Sloped Roofing Continued: Types of Systems

EPDM (Rubber)

EPDM is an elastomeric compound synthesized from ethylene, propylene, and a small amount of diene monomer; it’s a synthetic rubber material that can be formulated with a great deal of flexibility for use in roofing. EPDM membranes exhibit a high degree of ozone, ultraviolet, weathering, and abrasion resistance, and have good low-temperature flexibility. EPDM’s properties of resilience, tensile strength, elongation, and hardness are largely retained in aging tests at elevated temperatures.

EPDM has been used as a roofing material in the United States since the early 1960s. EPDM sheets range in thickness, from 30 to 90 mils, both reinforced and non-reinforced, and are usually black or white in color (sheets formulated with titanium dioxide produce a white membrane); they can also be coated to create an aesthetically pleasing appearance.  All seams involved on a EPDM or rubber roof must be adhered. EPDM is the most often installed single-ply roofing membrane system, accounting for about 40 percent of the commercial roofing market.


Thermoplastic olefin (TPO) membranes are produced from polypropylene and ethylene-propylene polymers, and may include flame retardants, pigments, UV absorbers, or other ingredients as part of their formulations. TPO sheets range in thickness, from 45 to 80 mils. TPO is considered the new membrane, with claims of recyclability and environmentally friendly materials.

TPO-based products have been used in various applications, including the automobile industry, since the 1980s. In 1989, TPO-based membrane appeared in the roofing industry as a non-reinforced sheet. In 1993, the original non-reinforced TPO membrane was replaced with membranes containing reinforcing fabric. Since that time, the TPO single-ply roofing market has grown significantly, and some industry reports state that TPO is the fastest-growing segment of the U.S. single-ply roofing industry.

Unlike other popular thermoplastic roofing membranes, TPO polymer doesn’t contain chlorine, and no chlorine-containing ingredients are added during sheet production. This lack of chlorine has allowed TPO marketers to tout their membrane as an environmentally safe, green product.


Polyvinyl chloride (PVC) roofing membranes have been produced and marketed as early as during the 1950s in Europe and gaining momentum in the U.S. in the 1970s once a larger range of thickness was put into play.  Using either glass fiber or polyester to reinforce, PVC roofing membranes are considered thermoplastic materials. Because of the material’s chemical nature, some thermoplastic membranes may be seamed by heat welding (hot air as opposed to glue), seaming with tape products, or solvent welding. The seam is almost indestructible when properly made, and does not fail when under water for extended periods of time. Ponding water exclusions aren’t part of the warranty. Many reinforced PVC roofing membranes perform properly with a life of 30 years or longer.

Some PVC membranes are available with a factory-applied adhesive backing and release film adhered to the underside of the sheet (referred to as the adhered peel and stick system). PVC membranes can be produced in numerous colors, although gray and white are the most common.

Modified Bitumen

Polymer-modified bituminous roofing membranes were developed in Europe in the 1960s, and were introduced to the U.S. market during the “single-ply revolution” of the mid- to late-1970s.

This particular type of roofing requires roofing sheets that should be used as multiple-ply systems. Most manufacturers now require at least a base sheet below their modified sheets. In the 1980s, these products became more widely accepted in the U.S. market, and they became their own membrane type, separate from single-ply membranes. In the late 1980s and early 1990s, the use of polymer-modified membrane roof systems grew significantly, including two roof system configurations: polymer-modified bitumen roof systems and the top layer in multiple-ply built-up roof membrane (or hybrid) systems. These systems account for approximately 17 percent of all commercial roofs.

Holt Roofing Company can assist you with not only installing any of these systems on your commercial building, but also repairing or replacing certain areas in need.

Contact Holt Roofing today to set up an appointment with one of our commercial experts on-staff – 419-478-2900.