Take a look at building construction on the Michigan State University campus and you may notice a common feature sprouting up: green roofs. Succulent foliage has started to emerge, very slowly taking the place of conventional gravel ballast rooftops.
A new facility built last fall to connect the Plant and Soil Sciences Building with the nearby Plant Biology laboratories sports a state-of-the-art green roof, along with some of the newly renovated dorms in the Brody complex. And this spring, the new Wells Hall addition is slated for an eco-friendly rooftop.
It's a building enhancement that Michigan State University AgBioResearch scientist Brad Rowe hopes to see more of. Rowe has been studying these living roofs on the university's campus since the first installation at the Plant and Soil Sciences Building in 2004. He explains that the new green roof -- the one installed last fall on the Plant and Soil Sciences Building expansion -- is dramatically different from the one planted there 8 years ago.
"Because of weight restrictions, the first one back in 2004 had a media depth of only 1.5 inches, which limits the vegetation to drought-tolerant succulents such as sedum," says Rowe, a professor in the MSU Department of Horticulture. "What makes this new green roof different is that its growing medium is mounded up 8 inches in the middle, allowing for a wider plant palette. I planted over 1,200 plugs of 17 native herbaceous perennials and grasses. It is part of a long-term research project to see what species live or die out."
Rowe studied the original Plant and Soil Sciences green roof for two years after its installation, comparing it with conventional roofing. In general, green roofs better insulate buildings – they keep roof temperatures lower in the summer and higher in the winter. Rowe found that summer rooftop temperatures with a green roof were up to 68 degrees cooler and that heat flux into the building was reduced by up to 167%.
Though MSU is now also home to green roof research platforms at the Horticulture Teaching and Research Center, the outdoor classroom at the MSU Children's Garden and several small research plots (raised beds) on the Communication Arts building, Rowe says the high costs associated with installation continue to be a major deterrent.
A typical green roof system is composed of 2 to 6 inches of lightweight, engineered soil that drains water, holds roots and nourishes the plants. Sedum is commonly used because of its drought tolerance and its ability to grow in shallow soil without irrigation. Many buildings require substantial structural enhancements to accommodate the extra heft of the soil and plants.
"The main roadblock still remains cost," he says. "Also, part of the problem in determining the value of a green roof is how to put a value on something like aesthetics, or measuring the community benefit of reduced storm-water runoff in our municipal sewer and storm-water systems, or improved human health due to less particulate matter in the air. Still, the more that are installed, the lower the costs."
An obvious advantage is reclaiming the vegetative footprint destroyed in the construction of a building, especially in urban areas. Rowe is exploring ways to utilize the rooftop space to grow fruits and vegetables in urban areas where access to fresh produce is limited.
"If there is ample land available at ground level, it probably makes more sense to do it there, assuming the soil is suitable for growing food," he says. "However, in many urban areas such as New York City, land at ground level is not available. Using rooftops to produce food is utilizing previously wasted space. I think it makes sense for home gardeners or community gardens where the produce is grown and consumed locally, but probably not for commercial production."
A disadvantage is that vegetables require irrigation and more fertile soils than succulents such as sedum, irrigation can lead to water runoff and pollution problems, Rowe said. These factors need to be quantified to see if they really are a problem.
The benefits of green roofs reach far beyond energy conservation, he adds.
"If energy was the only concern, it would be more cost-effective to just add more insulation," Rowe says. "You've got to add up all the benefits such as energy savings; mitigation of the urban heat island; carbon sequestration; storm water management; improved aesthetics; reduction in air, waste and noise pollution; improved human health; increased biodiversity; and increased longevity of roof membranes."
The MSU program began in 2000 when the university worked with Ford Motor Company to install a 10-acre green roof on an assembly plant in Dearborn, one of the largest in the world.
Green roofs are catching on across the globe. Rowe said the amount of green roof space in North America has been doubling each year since his research began.
"Most of these systems are on government and commercial buildings, but it's a growing business, and there continues to be a lot of interest."