EPDM Roofing Systems

Single-Ply Roofing

While built-up roofing (BUR) utilizes multiple layers of reinforcing and field-applied bitumen for the waterproofing, many MB systems use just two factory-coated sheets. EPDM goes even further, using just single layers of rubber and reduces field seaming by offering sheets in widths up to 50 feet. Many of these EPDM sheets also eliminate internal reinforcement entirely. While EPDM is the polymer of choice today, other elastomers have been used in the recent past, including butyl rubber, neoprene (chloroprene), polyepichlorohydrin, and Hypalon® (chlorosulfonated polyethylene or CSPE).

Basics of EPDM Rubber Roofing

  • The polymeric component is a blend of polyethylene and polypropylene with a small amount of an unsaturated diene, a monomer that contains multiple double bonds through which cross linking or vulcanization can take place.
  • Carbon black (consisting of extremely fine carbon particles) is added to act as an ultraviolet screening agent, as well as to increase the modulus of elasticity (increased tensile and tear resistance).
  • Inert fillers such as limestone reduce membrane costs.
  • Extending oil permits greater loading of low-cost fillers.
  • Curing agents, processing aids, and catalysts.
  • Fire retardants.UV- or ozone-resisting additives.

While most EPDM sheets are compounded with carbon black, white rubber has been attempted without much success. Currently, if a white roof is desired, a white coating is field applied after the EPDM membrane installation is completed.

EPDM membranes may be non-reinforced, generally for ballasted systems, or they may have internal scrim reinforcement for mechanically fastened systems where concentrated stresses are expected. Typical product thicknesses are 1.1 millimeters (or 0.045 inches), 1.5 millimeters (or 0.060 inches), and 2.2 millimeters (or 0.090 inches). MB sheets are typically 4 millimeters for cap sheets and 3.5 millimeters for base sheets. Fire-retardants sheets are available, but are not required to meet the building code when ballast is to be applied.

Energy Considerations

MB and single-ply systems require far less petroleum-based material than traditional bituminous build-up roofing.The most spectacular comparison would be a flood-coat and gravel surfacing on a BUR, which requires 7.5 gallons (60 pounds) of asphalt per roofing square, while a single-ply roof requires none.

While much attention has recently been paid to ENERGY STAR® reflective surfacings (most of which are white), an excellent case can be made for alternatives such as adding additional thermal insulation, the use of ballast with its increased thermal mass (thermal lag), and protected and vegetated roofs.

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