Architectural Record BE - Building Enclosure

Cool Roofs for a Hot Planet

Today's cool roofing systems are a significant platform for urban building sustainability
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Sponsored by Duro-Last®, Inc.

Brief History of Modern Roofing

For many decades, traditional asphalt roofing construction was the norm. Asphalt roofs experience little expansion or contraction, which means there were no thermal shock issues to consider. There was little concern for insulation and heat loss. Air-conditioning use was minimal or was not very costly. Therefore, summer heat retention was of not much concern.

Single-ply membrane products appeared in the early 1970s. Over the past few decades, scientists and product manufacturers developed better knowledge of chemical interactions and have introduced plasticizers and stabilizers into single-ply membranes, which prolong material life. At this point, the single-ply roofing industry has a proven performance record of more than 30 years.

As with any product, the quality of the components affects overall performance.

Types of Membrane Roofing

There are more types of membrane roofing than many architects realize. Modified bitumen, for example, is asphalt-based and blended with styrene-butadiene-styrene or atactic polypropylene. This product is a hybrid of traditional BUR (built-up roofing).

Thermoset membranes are “vulcanized,” which means the molecules are cross-linked, making polymers elastic. However, these materials become “set” so they are difficult to bond to each other. That means they cannot be softened and bonded by heat. Therefore, seaming requires adhesives. These include EDPM, Neoprene, and CSPE (Hypalon).

Thermoplastics will “flow” when heated because the molecules are not cross-linked. That means the seams can be heat welded or solvent welded. Ingredients used in compounding can include PVC resin, plasticizers, stabilizers, pigments, and fillers.

These materials are represented by a somewhat bewildering array of abbreviations: PVC, CPA, EIP, NBP, CPE, PIB, and TPO.

The big players of thermoplastics, however, are TPO (thermoplastic polyolefin) and PVC (polyvinylchloride).

TPOs are relatively new in the field, with most having been installed in the past 15 years. The ASTM standard for TPO is ASTM D 6878-03 for TPO Based Sheet Roofing.

PVC membranes can be prefabricated to fit each roof and penetration.

Photo courtesy of Duro-Last, Inc.

PVC membranes can be prefabricated to fit each roof and penetration.


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Originally published in Architectural Record