By Edward Betker, RRC SHRINKAGE OF EPDM (ETHYLENE PROPYLENE Diene Terpolymer) synthetic rubber roof membranes is a known potential performance problem. The shrinkage becomes a problem when it disrupts mem¬ brane securement, membrane flashings, and, in some instances, other building components at the perimeter and interior roof details. It has been recognized as a long-term performance issue by the roofing industry. The “shrinkage” addressed in this article refers to the chronic permanent dimensional change to an EPDM roof membrane, as opposed to expansion and contraction associated with normal cyclical temperature changes. In field observations, shrinkage is most commonly noted on loosely-laid, ballasted systems, and on some mechanically-attached assemblies. There have been attempts by several industry factions to provide a standardized response or typical repair recom¬ mendation to this phenomenon. Unfortunately, a standard¬ ized response or repair recommendation is not the best approach. Based on our experience, the range of the necessary responses has been from minor isolated repair to total roof replacement. EPDM manufacturers, following their warranty criteria, have responded to this phenomenon by performing isolated repairs in response to leakage only. This is often carried out too late if the leakage is due to shrinkage and the associ¬ ated detail disruption. This “band-aid’ approach treats the symptom, not the cause, which often allows serious perfor¬ mance problems (i.e., wet insulation, water entry) to con¬ tinue. How Long Should A Roof Perform? As a measure of comparison, some automobiles are current¬ ly marketed with a 36,000 mile bumper-to-bumper warranty. With appropriate maintenance, if today’s vehicles do not exceed that mark by a factor of three, something is wrong. The same holds true, although the factor is two, for EPDM roof systems with the standard ten-year manufacturers war¬ ranties. Twenty years is still the benchmark by which roof systems are measured on a life-cycle cost basis. It is no longer a complete surprise to recommend removal and replacement of an EPDM roof system with a longevity of much less than this benchmark. Perimeter detail disruption due to shrinkage and inadequate initial restraint- Note the insufficient repeated repairs. Evidence of membrane shrinkage which resulted in complete detachment of the original membrane restraint. Repair or Replace In many instances, EPDM membranes with the tendency to shrink may not need repairs if the membrane restraint was not adequate initially. When a recover application is chosen as a cost-saving mea- May 1998 Interface • 11 sure, proper membrane restraint is often one of the aspects which is also compromised in the name of minimizing initial expense. For many building owners, interior water entry is the first indication of a roof problem. In certain recover applica¬ tions, large areas of the recover insulation, if not the entire roof, can become saturated with water before interior water entry develops. Should shrinkage and related leakage occur in a recover application, complete removal and replacement may be the only reasonable alternative. The nature of the occupancy must also be considered when making a decision on the appropriate response to potential leakage from this phenomenon. A facility used for temporary storage of automotive tires intended for recycling does not face the same consequences if leakage occurs as a hospital, library, or communications facility. Each project needs to be evaluated on the basis of economics versus risks. The roof system’s age, past performance, and development of any addi¬ tional performance problems (i.e., splice delaminations), must also be considered. EPDM roof systems continue to be specified for clients when it is decided they are the most appropriate choice. With proper initial membrane restraint at the details, satisfac¬ tory performance and longevity can be achieved If detail dis¬ ruptions do occur due to shrinkage, timely and appropriate remedial action is necessary. We recommend membrane securement exceed industry minimums. Some factions of the roofing industry have, to date, not required higher standards of membrane securement. It is clear that proper membrane restraint is paramount for long-term satisfactory performance of an EPDM roof system. About The Author Edward Betker is <1 registered roof consultant with PCI He has been in the roofing industry since <977. Betker has been with INSPEC, Inc. of Minneapolis, MN for the past 20 years. His experience includes evaluation of roof performance on all types of systems and serving as an expert witness for roofing-related litigation. 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With an accuracy to 0.25% of full scale, the 1500 pound capacity digital gauge often eliminates the need for multiple gauges to J cover the force ranges required by the * many fasteners in the roofing industry. —^^^COMTEN INDUSTRIES 1124 – 19th Street North, St. Petersburg, FL 33713-5724 • Phone 813-822-3508 • FAX 813-895-2328 Visit us in Booth 78 ‘ at RCI in Dallas. k Interested in advertising in Interface? Just call 1-800-828-1902. May 1998 Interface • 13
