Green Roofs Are Getting a Big Trial in Hoboken

The movement toward green building and sustainability-minded development is at an odd crossroads. On one hand, some progressive cities have made regulation strides toward more energy-efficient and less environmentally harmful building practices, while a viable industry has grown up around green construction and roofing materials. On the other hand, the mounting damage of climate change can make sustainability efforts look like window dressing, and the prospect of building green, especially when it comes to retrofitting existing buildings, remains costly.

Still, daunting as the climate threat may be, the environmental benefits of green building and stormwater management are clear. Green roofs in particular have been shown to reduce rainwater runoff, filter pollutants, reduce energy usage and cool cities overall, diminishing the “urban heat island effect.” They also benefit bird populations and have even contributed to an uptick in urban birdwatching. This fall, researchers at the Stevens Institute of Technology in Hoboken, New Jersey, are launching a “living laboratory” on the roof of a new campus building, with hopes of learning what types of green roofing materials work best.

The lab consists of various green roof setups, rain gardens and planters designed for optimal stormwater management called “bioretention” planters. The four planters are tricked out with soil sensors to monitor how much water, flowing out of a downspout, is captured by the “medium,” the mix of sand or soil that the plants take root in.

On top of the roof are 19 different green roof setups — picture a small tabletop garden — each with a different engineered medium. Researchers hope that, by the end of the fall semester, they’ll be able to start analyzing data about which mixes work best for retaining water and filtering pollutants. Each setup is duplicated, for a total of 38 setups, so that the results can be verified.

“The hypothesis for our research is that the aggregate type matters,” says Elizabeth Fassman-Beck, an associate professor at Stevens and co-author of the book “Living Roofs in Integrated Urban Water Systems.” “In other words, not all sands or rocks are created equal when it comes to influencing water movement.”

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