Elastomeric roofing based upon ethylene propylene diene terpolymer (EPDM) has been around for more than four decades and can claim 500,000 warranted roofs consisting of 20 billion square feet in place.
If one of these roof systems are on your buildings, you may not need a costly roof replacement just yet. Examine your roof to see if any of these EPDM fixes will work for you.
The Components of EPDM Roof Systems
Elastomers are defined as macromolecular materials that return rapidly to their approximate initial dimensions and shape after subsequent release of stress.
In contrast, thermoplastic materials will deform when stressed but not fully recover when the stress is removed. Thermoplastics include polymers such as polypropylene, polyvinyl chloride (PVC), chlorinated polyethylene, ketone ethylene ester (KEE) and chlorosulfonated polyethylene (Hypalon, which crosslinks upon weather exposure). Thermoplastic materials can be joined together (usually by heat welding), unlike elastomers, which cannot be heat welded.
EPDM combines two thermoplastics, ethylene and propylene, with a diene that permits the ethylene-propylene chains to be crosslinked. During vulcanization, this converts the properties of a roof membrane from a weldable thermoplastic to an inert, long-life, heat resistant elastomer.
During the early 1960s, these elastomeric properties were achieved through vulcanization of polymers such as natural rubber, butyl, neoprene, styrene butadiene rubber (SBR), chlorobutyl, polyepichlorohydrin, silicone, and other polymers. However, it has been demonstrated that only EPDM possessed the necessary combination of properties for long roof life and cost efficiency, confirmed by many roof systems that are still in service after 30 years or more.
As with the tires on our automobiles, carbon-black reinforced EPDM membranes have proven to have extraordinary weather, UV, and ozone resistance as well as enhanced physical properties. While white pigmented EPDM is available, indications are that the black material is, and will be, more resistant to UV attack over its long life.
Extend EPDM Roof Life
Remarkable as the original EPDM rubber membrane roofs were, they have evolved to address changes in application techniques and systems over time. Most of these upgrades relate to seaming, attachment, flashing, and edging. Could your roof benefit from an upgrade? These four issues with existing aged membranes offer the greatest potential benefit.
1) Seaming and T-joints. Early systems for joining side and end laps of sheets required several steps, each of which required skilled workmanship. These included wiping the membrane to remove surface talc (a release agent needed during the vulcanization step) and accumulated dust and dirt so that wet-applied adhesives would adhere to the membrane. The solvent-based adhesive was applied to the surface of the membrane and the intended overlying EPDM, then checked with a knuckle to make sure the adhesive was tacky but not wet. A steel roller was used to insure proper embedment of the membranes into the adhesive.
Today, solvent-free tape is usually either field or factory-applied to laps, replacing the wet adhesives of previous generations and insuring a more uniform adhesive thickness. With the adhesively bound seams, a pumping grade of seam caulk was applied to the exposed edge of the seam so that moisture would not infiltrate and degrade the adhesive layer seams.
In the case of rehabilitating an existing EPDM roof membrane, it is impractical to examine every inch of suspect or delaminated seams. Instead, it is recommended that weathered surfaces are cleaned for several inches on each side of all field seams and that a cover strip of fresh EPDM membrane is applied.
A T-joint, where three layers of membrane come together, is especially vulnerable to moisture penetration. For older EPDM roof systems, a target piece of self-adhering membrane can be centered over the T void during renovations to the EPDM membrane.
2) Shrinkage of EPDM roof membranes. While fully adhered and mechanically attached EPDM roofs generally resist to shrinkage over time, ballasted membranes sometimes demonstrate shrinkage at penetrations and roof perimeters.
The Midwest Roofing Contractors Association (MRCA) and later the National Roofing Contractors (NRCA) offer a step by step guide to repairing and re-attaching EPDM membranes and flashings, which will be valuable if you notice shrinkage during an inspection.
3) Restoring displaced ballast or reattaching EPDM membranes. Where roof perimeter ballast has been displaced by wind scour, add additional larger diameter ballast (assuming the additional weight is allowed). Many codes require 10 psf of #3 or #4 (nominally 1.5 in diameter) stone for the field of the roof, but you can upgrade to 17-20 psf of larger stone (2-.5 in diameter) in perimeters and corners. Alternatively, you can use pavers in these critical areas. A comprehensive document on designing ballasted roofs for wind resistance is available on the SPRI website as ANSI/SPRI RP-4.
Where adhered systems have become detached, such as delamination at the interface of the membrane and thermal insulation/coverboard, it may be possible to re-anchor everything by using a mechanically fastened system installed in an approved pattern. Fasteners or battens would then be covered with a fresh strip of membrane.
4) Repair of flashings, edgings and penetrations. Of all the changes made in EPDM systems over the years, upgrading or replacement of vertical flashings is the most dramatic. First generation materials consisted of uncured neoprene (chloroprene). It turned out that the neoprene would not only cure with weather exposure as intended, but it would also embrittle, especially on south-facing exposures.
If such failures are detected during routine surveys, your options are to remove the failed material and start over or overlay the walls and curbs with plywood or OSB and reflash with new EPDM-based material. Penetrations are best treated by removing existing material and either installing premolded boots or pourable curing compounds into pitch-pockets.
Metal edgings have evolved over the years to take advantage of the unique flexibility of single-ply materials. Most edge details now show turning the flexible roof membrane down over the fascia, followed by installing a raised metal fascia cover.
The Future of EPDM
The evolution of EPDM systems with thicker membranes, internally reinforced and fleece-backed sheets, tapes replacing wet adhesives and improvements in factory seaming and Quality Control, flashing and edge details suggests that today’s systems will be even more durable then previous generations. On top of that, when replacement is ultimately necessary, recycling of non-adhered EPDM sheet material is a viable alternative to relegating the old roof to a landfill destination.
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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