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Roofing technology developed in Germany is starting to take root in North America

By Nancy B. Solomon, AIA

Plowing ahead

Today, about 10 patented green-roof systems are available from about two dozen companies in North America. Each company typically offers full service for a complete green-roof system, from membrane to plants. According to Schickedantz, however, an architect can, and often should, mix and match proprietary components to suit a project’s particular needs.

Some of these companies strictly focus on green roofs; others are traditional roofing manufacturers that are adding green to their palette. In either case, the American firms have typically aligned themselves with a German green-roof manufacturer and modified the German technology to suit North American building requirements and climatic conditions. However, the jury is still out as to whether these systems have been fully adapted to our continent. And there is not yet enough hard data distilled from rigorous testing—here or, for that matter, in Germany—to show quantitatively how well green roofs succeed in their expressed goals.

Fortunately, a few researchers in academia are beginning to rectify the situation. For example, Bill Hunt, P.E. (www.bae.ncsu.edu/people/faculty/hunt), extension specialist with the biological and agricultural department at North Carolina State University in Raleigh, has set up three experimental roofs to investigate, among other factors, the speed at which water runs off both conventional and green roofs, measure how much nitrogen and phosphorus are absorbed by the systems, and determine the optimum roof slope, soil type and thickness, and plant species for the southeast United States.

Despite the various systems currently on the market, Hunt admits that there are still a lot of design questions to be answered: How thick should the soil be? What type of soil should be used? What are the best plants for quick growth? How does soil depth affect plant growth and flood reduction? “Right now it’s a shotgun approach,” confesses Hunt. But not for long: “Soon there will be enough data so that we can make pretty good preliminary design recommendations,” he predicts.

In the meantime, to further their education, architects interested in this new technology may want to attend Greening Rooftops for Sustainable Communities: The First Annual North American Green Roof Infrastructure Conference, Awards, and Trade Show. It takes place on May 29 and 30, 2003, in Chicago and is cosponsored by The City of Chicago and Green Roofs for Healthy Cities.