TPOs TPO technology was first brought to the roofing industry in the mid-1980s as an alternative to the most popular single-ply materials: EPDM and PVC. The TPO product combines the best elements of both rubber and plastic membranes. The result is a membrane that is ideal for commercial roofing applications because of strong physical property characteristics, such as resistance to UV degradation and heat aging, cold-temperature flexibility, puncture-resistance and tear strength.

In addition, TPO materials are highly resistant to a wide variety of chemicals including animal fats, acids/bases and vegetable oils. This property makes them suitable for direct contact with most common roofing materials. Although TPO materials are not inherently fire-resistant like PVC roofing materials, which contain halogen, TPO roofing membranes can be made both fire-resistant and highly weather-resistant during manufacturing.

One of the most outstanding features of TPO membranes is heat seamability, which allows the material to be welded together vs. glued or taped like other types of membranes. The result is better seam strength compared with the adhesive sealed method, which aids in waterproofing.

"Seams are often the weak point of any roof, so the stronger the seam, the stronger the roof," says GAF Materials' Bailie. GAF Materials is building a new TPO plant in the Midwest that is expected to be operational by third-quarter 2000.

"The big advantage of TPO over EPDM is the installation of the product," agrees Gallivan. The TPO seams are heat weldable as opposed to the taping or gluing methods used to seal EPDM seams. In addition, TPO can be applied in all seasons, whereas EPDM is subject to temperature restrictions because of the glues and tapes necessary for installation.

TPOs also are much stronger than PVC membranes, and TPOs are not under the environmental attack that PVCs are because of chemicals contained in the material, Gallivan reports. Plasticizers added to the PVC product have a tendency to leach out, which has a negative impact on the environment while also leaving the membrane brittle.

"I think if it's done properly, TPO gives a very good seam. That's not to say that it's foolproof," Ducharme says. "On the EPDM side, we're doing things to improve the consistency of the seaming. So the two products are very comparable."