On Green Roofs

Thanks for providing another thought-provoking feature (EBN

Vol. 10, No. 11). As a result, I hope more of your readers will view the roof as a green-design opportunity. Although rooftop PV systems may be the most ecologically productive use of a roof, a well-planned vegetated roof has enormous green building value. A cautious approach to all (especially green) roofing is justified, however, I think your readers would benefit from a more in-depth discussion of the waterproof membrane component.

Concealed waterproof membranes (quite different from exposed roof membranes) fill a small and specialized niche in the construction industry. Over the years, numerous waterproofing products (coal tar pitch, urethane-modified asphalt, self-adhered sheets) have been used with limited success for horizontal deck applications. For performance reasons, the general consensus has shifted to hot fluid-applied rubberized asphalt, SBS and APP modified bitumen sheets, and PVC sheet membranes. While each product can provide a watertight solution, the individual environmental profiles vary. For inexperienced waterproofing designers, selecting a proven waterproof membrane type may reduce the risk of green roof failure. In addition, the experienced designer may want to also investigate one of the lesser known (yet promising) systems including heat-weldable EPDM (filler-free), cold fluid-applied elastomerics, and various fluid-applied and sheet (field fabricated) composites.

In addition to selecting the proper waterproofing materials, a knowledgeable contractor and field installation crew is priceless. Unlike traditional roofing contractors, those companies with extensive deck waterproofing experience (like PMR assemblies, below-grade vaults, and plaza decks) are often better prepared (than traditional roofers) to install a watertight membrane that will withstand the test of time and soil overburden. In short, the best construction documents and materials can be compromised by faulty workmanship.

Subscribing to the current roofing paradigm (planned obsolescence), many design professionals, contractors, and building owners have long relied on the convenience of exposed roof membrane for easy repair and maintenance. This luxury no longer exists for the owners of a “buried” green roof membrane. Fortunately, the (protected membrane) design of a green roof system eliminates the source of membrane deterioration. Hidden from UV rays, the membrane service life is greatly increased. And so the perceived risk is only that which is created by our lack of waterproofing-design education—not knowledge.

Like other protected membrane roofs, the foundation of a successful green roof installation begins with a reliable waterproof membrane. Only then can green roof design endure.

Steve Shull

e-Roof, inc.

Deerfield, Illinois