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Biologists and Architects Innovate Vegetated Rooftops to Link Cities With Natural Systems

What some call a sustainable answer to urban flaws, Anna Droz calls research. As a biological sciences doctoral student in ������’s College of Arts and Sciences, Droz’s curiosity has developed into a passion, maybe even an obsession, to discover the best vegetative roof combinations with the optimal plants, soil, and micro-organism communities.

Just like the name implies, vegetative — or “green” — roofs are man-made green spaces that connect the tops of buildings to the larger environmental context. Besides the aesthetic benefit, they can grow produce, catch storm water, control temperature, provide habitats for wildlife, and simply turn an unusable rooftop into a local amenity. Often times, these systems require additional materials to deliver these public and private benefits.

“Design is limited,” said Droz. “Roofs are not meant to support a lot of weight. So, a lot of times these designs end up being this very thin layer of non-native plants. They are still good, and can catch storm water, but they’re not as sightly to look at and don’t provide many benefits, such as thriving habitats for pollination and things like that.”

Droz initially learned about green roofs as part of a multi-disciplinary design team consisting of undergraduates, graduate students, and faculty from CAED, Biological Sciences, and Geology. The team was funded by a grant from the Environmental Protection Agency to Dr. Reid Coffman, associate professor in the College of Architecture and Environmental Design (CAED); Dr. Christopher Blackwood, professor of Biological Sciences; Dr. Rui Liu, assistant professor in CAED; and Dr. Anne Jefferson, associate professor of Geology. The team met weekly during the 2014-2015 school year. After hours of sketching out, modifying and testing ideas, they eventually developed a new type of plant and soil-based technology to reduce stormwater runoff and enhance biodiversity that could be deployed in a variety of situations, from roofs to industrial brownfields. The design project culminated in a presentation at the 2015 EPA P3-People, Prosperity and Plant Design Competition in Washington, D.C. From there, Droz, Blackwood and Coffman set out to answer another question: Is there a way to make roof-top gardens better?

Their quest took them to the heart of the Midwest, where they toured and sampled nearly 50 roofs. In Minnesota, the team explored the rooftop of the American Swedish Institute in Minneapolis, the St. Paul Fire Headquarters and another on top of the Minneapolis Central Library. She also toured the gardens atop the Peggy Notebaert Nature Museum and the Hyatt Regency building in Chicago.

What the team learned, they brought with them to the Cleveland Industrial Innovation Center, where they built 48 one-meter square plots to compare different types of green roof options. Each plot boasts a unique ecosystem. The new technology developed for the EPA-P3 Design Competition is represented alongside a centuries-old traditional design and a commercially available green roof system. Some plants are the standards commonly selected for green roofs, while others are modeled after a prairie community naturally found in Ohio.

The team also added special microorganisms to some plots, in hopes they will colonize and boost the health and functioning of the plants.

As Droz collects data, she is comparing the plots to see which look the best and which are the healthiest. Her next step will be to look at the soil and water quality and ultimately share her research findings.

“I’m hoping that by answering these ecological questions, we can add a bit of realism to green infrastructure and environmental architecture,” Ms. Droz said. “The field is growing and people are optimistic, but there isn’t a lot of science going into it. If this is going to be everywhere, we want to make sure that we know what works and why.”