- Category: Green Buildings
16 Oct 2012
- Published on Tuesday, 16 October 2012 12:21
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Two hardy flowering grasses blossomed as the best choices for “green roofs” in a recent pilot study done by the University of Cincinnati.
Green roofs, which can use vegetation to shade surfaces and remove heat from the air, are a sustainable building technique that can reduce a building’s energy use by lowering its temperature and those of the surrounding area. (See related story.)
“There are many potential benefits to green roofs, including building energy savings, extension of roof life, reduced air and noise pollution, creation of environment for native birds and insects and, of course, reduced storm water runoff,” said Ishi Buffam, assistant professor of biology.
Mr. Buffam, along with University of Cincinnati biology student Jill Bader, identified the nodding wild onion (Allium cernuum) and the goldmoss sedum (Sedum acre) as suited to survive and thrive in hot, dry conditions with minimal watering – conditions found in rooftops in the Midwestern region.
“We tested the plants because one of the most critical choices for the success of a green roof is the choice of plant species,” said Ms. Bader.
According to Ms. Bader, the environment on a rooftop is characterized by severe drought, elevated temperatures, high winds and shallow layers of soil – conditions that could be tough for plants not bred for similar environments.
All in all, four Ohio native plants were tested – the goldmoss sedum being a European transplant. These plants were selected because their natural habitat is prairie or meadow, where exposure to full sun and dry conditions are typical.
The plants were tested under two conditions – getting their water from rainfall only or receiving regular watering.
All plants receiving regular watering survived but three species, the heath aster (Aster ericoides), flowering spurge (Euphorbia corollata) and lanced-leaved loosestrife (Lysimachia lanceolata) couldn’t survive on rainfall alone.
In contrast, the nodding wild onion and the goldmoss sedum managed to survive while only receiving rainfall as water source.
The researchers noted that both of these plants have shallow root systems and can efficiently use water during hot, dry conditions – two characteristics that could account for their good survival rate.
Mr. Buffam and Ms. Bader also tested the plants’ ability to reduce water runoff, an important function of a green roof. They found that the plants receiving regular watering retained 44 percent of rainfall on average while those getting their moisture from rainfall retained 51 percent.
“Our research will help inform the design of green roofs specific for this region, and therefore increase their chances of being successful, and being adopted in Midwestern cities,” said Mr. Buffam.
This pilot study was supported by the University of Cincinnati’s Julia Hammler Wendell Scholarship Fund, Women in Science and Engineering (WISE) Program and Cincinnati Center for Field Studies at Miami Whitewater Forest, a research station partnership between the University of Cincinnati and the Hamilton County Park District.