Chris Higgins, Oregon State engineer (Photo: Frank Miller)

Growing greenery on roofs brings many benefits. Buildings stay cooler, saving energy. Roofs last longer, saving money and materials. Birds and insects find new habitat, helping ecosystems. And green roofs make urban spaces more aesthetically and spiritually pleasing, as well as reducing heat-island effects for city dwellers.

But there are some costs that need to be considered, too. “Eco-roofs carry higher gravity loads and must support more moisture for longer periods than traditional roofs,” says Oregon State structural engineer Chris Higgins. “That changes the probabilities that need to be considered during design. In order to extract all the benefits of eco-roofs, we need to ensure their structural safety. That requires research.”

Photo courtesy of City of Portland

One big question: Are green roofs safe during earthquakes? Led by Higgins, engineers in the School of Civil and Construction Engineering at Oregon State are undertaking the first comprehensive study of the seismic performance of eco-roofs with funding from the National Science Foundation. Using a full-scale simulated eco-roof, they will investigate drainage characteristics, load distribution of water-saturated soils, long-term service performance and the behavior of different planting materials during lateral shaking. Their findings will guide the development of standards for eco-roofs in seismic zones.