Rooftop Research

FAYETTEVILLE, Ark. — Green roofs reduce storm water run-off, cool city streets and cut energy costs. They also cost more than conventional roofs. Mark Boyer, a professor of landscape architecture at the University of Arkansas, wants to gather data that will allow building owners across the United States to cash in on the big-picture benefits that green roofs offer.

With Jon Lindstrom, an associate professor of horticulture, and students from the landscape architecture and horticulture departments, Boyer will begin research Tuesday, Oct. 17, by planting more than 6,000 Fame flowers, sedums and other succulents on the roofs of two new buildings in The Gardens, the tailgating area on the south side of the University of Arkansas campus.

Although planted roofs are gaining ground — 2.5 million square feet of green roofs were planted last year, a 72 percent increase from 2004 — research is lacking, Boyer says.

“The materials for green roofs cost more than conventional roofs,” Boyer said. “But if we can show that they reduce storm water flow, then developers and their clients may be able to reduce the size of pipes and detention ponds, the traditional tools for managing storm water. That means less cost for storm water components and more land for building, which is money in their pockets.”

Boyer is working with Findlay Edwards, an associate professor of civil engineering, to monitor storm water flow from the roofs. Flumes outside of the buildings will measure water flow following storms, while interior drainpipes are designed so that water samples may be taken and evaluated for pollutants and trace elements.

“My ultimate goal is to change policy, and those who set policy want hard data,” Boyer said.

Boyer also plans to lower maintenance costs by pinpointing which plants thrive where.

“Every geographic region of the United States is going to have a plant palette that’s suitable,” he said. “We can’t use broad brushstrokes. We need to find out what plants work where for green roof applications.”

Boyer chose not to irrigate the roofs: “Philosophically I have a problem with that. I’d rather look for a more sustainable solution,” he said. Instead, he worked with Jon Lindstrom to select hardy plants that will withstand Arkansas’ summer droughts and winter cold snaps.

“Most of the green roof experiments are taking place on the East Coast and in the upper Midwest,” Lindstrom said. “Until we get the plants in the roof and established, we don’t really know how they will grow here.” Eventually, Lindstrom hopes to propagate and test native plants on the roofs.

Boyer is working with researchers at Michigan State, Penn State and North Carolina State to expand the scope of his research. Plans call for the installation of identical 8-foot by 8-foot garden sheds at the four universities, so that controlled experiments may be conducted to identify the best plants for various regions and to collect extensive data on the storm water benefits of green roofs. They also will monitor energy use of the buildings to determine how green roofs perform in diverse climates.

The project, which Boyer values at $10,619, comes at minimal cost to the University of Arkansas. Emory Knoll Farms, a leading supplier of green roof plants, donated more than $3,000 in plants. JDR Enterprises donated the drainage layer and Chandler Materials provided the lightweight growing medium required for rooftop applications. Circulation paths needed for routine maintenance were covered by the donation of aluminum edging from Permaloc Corp. and pea gravel came from Schwartz Stone. Professional Landscaping donated organic compost and assisted with hauling; the UA horticulture department also helped haul materials.

Though some skeptics on campus expressed doubts about the performance of green roofs, Mike Johnson, associate vice-chancellor of facilities, viewed the project as an opportunity to prove that they work.

“We have bits and pieces of sustainability showing up all over campus, and this is another opportunity to add to that repertoire,” Johnson said, noting the university’s recent use of harvested rainwater for cooling, permeable Grasscrete paving in a parking lot and other green initiatives. “We have so much expertise on campus, and we’re trying to partner more and more with departments, landscape architecture foremost among them,” he added. Johnson hopes to tackle a larger project in the next few years, possibly including a green roof on a parking deck planned for the Garland/Douglas area north of the university.

 “They’ve gone out on a limb to get green roofs established on campus,” Boyer said. “There’s a think globally, act locally kind of thing going on.”