In an effort to cool buildings, reduce stormwater runoff and restore the natural environment, cities increasingly are turning to "green roofs." Municipalities can't rip up the concrete and steel that cover the urban landscape, but they can use rooftops to bring nature back to high-density areas.
Green roofs are rooftops that are covered with vegetation. Planted over waterproof materials, they often include underground irrigation devices such as the KISSS Subsurface Capillary Irrigation system. KISSS is the most advanced subsurface irrigation system available, sustaining plant growth while reducing evaporation. Traditional roofs soak up the sun's energy and return it as heat. In contrast, green roofs enhance the environment by lowering air temperatures, absorbing rainwater, reducing runoff, and creating wildlife habitats.
Green roofs combat air pollution and bring urban areas "back into balance" with nature, said Edmund C. Snodgrass, a green roof expert from Maryland who and has collaborated with colleges and universities to research the subject. "There is no factory in the world that makes oxygen for atmospheric consumption," he said. "Every bit of oxygen we breathe is produced by plants."
To fight global warming, society must reduce its carbon footprint. Conservationists envision a day when someone flying over major U.S. cities will look down and see hundreds of patches of green where there once had been only concrete, pavement, steel and glass. According to the U.S. Environmental Protection Agency, green roofs, which are increasing in use, can reduce greenhouse gas emissions.
The potential for covering many of the nation's urban rooftops with vegetation "is very exciting," said Dan Silver, executive director of the Los Angeles-based Endangered Habitats League. "It has the benefit of supplying habitat for some native species, such as birds and butterflies."
As recognition of the value of green roofs has grown, so has the use of government regulations to encourage their use.
"There are a number of cities now that are encouraging green roofs, most notably in the East where the biggest stormwater problems are," Snodgrass said. "There is Toronto, New York, Philadelphia, Washington, D.C., Chicago. In the West there is Portland and Seattle."
Living roofs that use subsurface irrigation systems produce plants with deeper and stronger root systems. The KISSS system was used in the creation of state-of-the-art living roofs at the Target Center in Minneapolis and the William J. Clinton Presidential Library in Little Rock, Arkansas. The Clinton facility is the first presidential library to earn an award from the U.S. Green Committee for environmental design.
KISSS capillary subsurface irrigation can be used in any green roof application. Subsurface irrigation uses a capillary action to deliver water directly to the root zone of plants and lawns. The system helps protect the environment because:
- The subsurface technology makes sure that water distribution is efficient. You only water the areas that need it and there is no waste.
- The system is the most efficient water delivery method available for rooftops, often saving more than 50 percent over conventional sprinkler designs.
- It is an intelligent system that moves water from wetter regions to drier soil, distributing it more quickly and evenly than other products.
- By delivering water directly to the roots, it eliminates evaporation and surface runoff.
Although new technology is bringing green roofs to modern commercial buildings, the basic concept is far from new. American pioneers built houses with sod roofs in the 1800s. Green Roofs have been used for centuries in Scandinavia. Even ancient civilizations recognized the benefits of bringing gardens into the urban environment. Greek historians considered the rooftop gardens of Babylon to be one of the wonders of the ancient world.
Communities that are striving to conserve water and fight global warming today recognize that living roofs make sense. The Environmental Protection Agency reports that built out areas are warmer than nearby rural areas, forming "heat islands." This increases summer energy use, air pollution and greenhouse gas emissions. According to the Green Roofs for Healthy Cities trade group, the green roof industry grew by 16.1 percent in North America during 2009. Chicago was the leading city with more than 500,000 square feet installed. Other top-ranking cities included Washington, D.C., Minneapolis, Baltimore, New York, and Milwaukee.
Brad Rowe, a professor of horticulture at Michigan State University, said benefits from green roofs are too numerous to ignore. "One of the benefits is the roof is protected from extreme temperature fluctuations, so it lasts longer," he said. "Then you throw in energy savings. Combine that with stormwater. A green roof can keep a lot of the water from entering the system."
If people want to bring plants and gardens into urban areas, there is no place to go but up, said Snodgrass. "The roof area is somewhere between 25 and 40 percent of the city," he said. "The only really large-scale place available to plant is on rooftops."