In past articles of our newsletter, we have advised caution when considering the use of new products. We're especially wary of anything described as "miraculous groundbreaking, or state-of-the-art". We're starting to see some pretty lofty claims for a "new" family of roofing materials referred to as TPO (or thermoplastic olefin).
TPOs were developed in the 1970s and have been used in the manufacture of many familiar items (such as golf cart bodies, inline roller skates, air bag doors and membranes for below-grade applications). They seem to make very good golf cart bodies. They may also make very good roof coverings; but the properties desirable in golf carts are less so in roofs.
TPO roofing materials derive from a blend of polypropylene plastic, propylene rubber, ethylene propylene diene monomer (EPDM) and various additives. The intent of the blending is to exploit the desirable properties of single-ply EPDM (or rubber) and PVC membranes in order to produce a material that is more resistant to environmental, physical and chemical stresses, that remains flexible and can be heat-welded.
While TPOs have risen in popularity, there remain some unresolved issues.
1. There are several brands of TPO roof membranes available with differing formulations and physical properties.
a. Some products are stiffer than others and there could be problems with these stiffer membranes where flexibility is required (at transitions, flashings, etc).
b. Some TPO membranes are not reinforced. Unreinforced EPDM and PVC membranes have experienced such problems as limited puncture resistance, shrinkage and brittleness. Some of these characteristics are likely to exist to some extent in unreinforced TPO membranes as well.
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2. TPO membranes are not inherently fire-resistant; therefore, fire-retardant chemicals must be added. The effects of these chemicals on the long-term performance of the material remains to be seen. Remember FRT plywood?
3. The performance history of the TPOs in roofing applications is relatively short; however, a recent comparative study of roofing materials in The Construction Specifier suggests a probable life cycle of 13 years. Claims of 20 to 30 years performance would seem at best, overly optimistic. That same study also compared life-cycle costs for roofing materials and TPOs ranked among the highest, at $.37 per square foot, per year. Conventional built-up roofing ranked near the lowest at $.31 per square foot, per year.
According to a recent newsletter published by the National Roofing Contractors Association
(NRCA), we can "expect to see the beginnings of a major shift to TPO membranes, largely because of the huge capital investments made by several prominent manufacturers". Helping "prominent manufacturers" recoup their investments is not high on ETC's list of selection criteria.
Could TPOs represent the next great leap forward in roofing technology? Possibly, but the current evidence is not convincing and our advice is to let the other guys take the risk.
Kirk Parsons |
