The Low-Down on EPDM Roof Systems

12/10/2012 | By Richard L. Fricklas

Why this elastomer remains a popular choice

EPDM retains its popularity for its flexibility, stability, and torch-free application. But why do we treat it differently from other membrane roof systems?

EPDM vs. Other Membranes
EPDM is an elastomer, a rubbery material composed of long chainlike molecules (or polymers) that are capable of recovering their original shape after being stretched to great extents – hence the name, from “elastic polymer.”

The commercial roofing industry has used an number of elastomers over the past several decades, including neoprene, Hypalon, butyl, and natural rubber. However, only EPDM has been found to possess all the necessary properties for long-term performance at an economical price.

Contents and Critical Steps
During the early stages of production, the polymer, fillers, curatives, and fire retardants are blended in a high shear mixer, much like how plastic materials are processed. The difference is that the additional step of cross linking (vulcanization) transforms the material into an inert, thermoset membrane.

EPDM sheets come in large rolls with widths up to 50 feet. This reduces the number of seams that have to be joined under field conditions, which then minimizes the risk of error. Critical field steps may include:

  • Cleaning the surfaces that are to be seamed together by dry scrubbing or using solvent wipes. Use a separate primer/wipe if recommended.
  • Applying a mastic. Early seams may have used a solvent-based mastic, but more recently tape mastics have replaced the solvent-based products because the tapes provide uniform thickness and higher peel resistance.
  • Using these same steps to conduct EPDM maintenance activities, such as correcting membrane shrinkage.
  • Joining the roof membrane to many different materials, such as pre-manufactured boots.

Where to Learn More
Looking to dive deeper into EPDM installation and maintenance? An excellent source of information is available from the EPDM Roofing Association (ERA). (link to

For more information, check out ASTM D6369: Design of Standard Flashing Details for EPDM Roof Membranes and NRCA construction detail plates.

Richard (Dick) L. Fricklas was technical director emeritus of the Roofing Industry Educational Institute prior to his retirement. He is co-author of The Manual of Low Slope Roofing Systems and continues to participate in seminars for the University of Wisconsin and RCI Inc., the Institute of Roofing, Waterproofing, and Building Envelope Professionals. His honors include the William C. Cullen Award and Walter C. Voss Award from ASTM, the J. A. Piper Award from NRCA, the William C. Correll award from RCI, and the James Q. McCawley Award from the MRCA. Dick holds honorary memberships in both ASTM and RCI Inc.

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