Applying Green Roofs to Schools
Today’s educational institutions strive to provide students with superior facilities and a unique learning environment-on a limited budget. Although school boards and facilities managers probably never think of the roof as an opportunity to meet these objectives, a green roof can make several significant contributions.
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| Green roofs can be installed on smaller projects such as bike stands and other freestanding structures if a whole school roof is not feasible. Photo courtesy of Re-Natur Company, Germany. |
Green roofs, elevated roof surfaces covered entirely by a thin soil and vegetation layer, provide benefits in three areas that can be particularly important to schools. First, green roofs improve the built environment by storing and absorbing rainwater and reducing the negative environmental impact of sealed surfaces. Second, the roofs create a learning environment that students and staff can utilize in studies involving water and energy efficiency. And third, operation and maintenance efforts are reduced through installation of a cooling green roof that also protects the roofing membrane and can outlast conventional roofs.
As green roofs are becoming more accepted for office buildings, the trend also is expected to influence school and university design. And schools have a unique opportunity to educate both students and the community by promoting the benefits of green roofs.
What is a Green Roof and How Does it Work?
There are two different types of green roofs: extensive and intensive.
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| A gymnasium is located underneath this green roof. Photo courtesy of Re-Natur Company, Germany. |
Extensive green roofs range from as little as one to five inches in soil depth and weigh no more than conventional gravel-ballasted roofs. They are primarily built for their environmental benefits, not for access. Installing an extensive green roof is a creative alternative to the required and often costly conventional storm water management controls. Green roofs absorb rainwater, reduce peak flows and runoff, and allow excess water to slowly percolate through the soil so it is treated by the time it reaches the drainage outlet. Waste is further reduced when plants absorb nitrogen and phosphorus as nutrients, eliminating what otherwise would become non-point source pollution.
Intensive green roofs, in contrast, require a soil depth of at least one foot in order to create a more traditional roof garden, with large trees, shrubs, and other manicured landscapes. Intensive green roofs add considerable load to a structure and require significant maintenance. The roof gardens, however, are designed to be accessible and can be used as outdoor laboratories for schools-a tremendous advantage in urban locations.
Why Green Roofs?
If green roofs, with their positive environmental impact, are incorporated into school buildings, they potentially can result in great savings. For example:
- Water Management– Schools usually are constructed as low-level buildings that take up a lot of land. The newly sealed- off areas generate runoff because water is no longer able to infiltrate the ground, necessitating the construction of storm sewers. However, storm sewer construction and maintenance is very expensive. Green roofs help by retaining 75 percent of the water-on average-which is stored in plants and in the soil layer. The roofs also trap sediments and other particles and actually treat excess runoff in events of heavy rain.
- Energy Efficiency – It is difficult to estimate the savings a green roof provides through energy efficiency because much depends on the design of the building. Nevertheless, schools are poised to take advantage of green roofs since many are one- or two-story buildings that enjoy far greater energy savings than multi-story structures. Green roofs, even with a soil and vegetation layer an inch and a half deep, prevent energy loss through the roof because of its thermal insulation properties.
- Urban Ecology – Cities often exclude greenery and nature in exchange for progress. While green roofs are no substitute for open space and simply cannot replace the significant functions of forests, prairies, and open parkland, they do provide green space and wildlife habitats from which both urban and suburban areas can benefit. Air quality in urban centers often is hot and dry due to the lack of trees and green space. For example, on hot summer days air temperatures reach 95°F or higher while roof surface temperatures can reach 175°F. The results include the urban heat island effect and a higher rate of energy consumption. A green roof’s plant foliage transforms heat (energy from the sun) and soil moisture into humidity through photosynthesis and reduces roof surface heat gain. The vegetation layer traps air and prevents rapid air exchange, thereby improving a building’s energy performance.
How Do Schools Benefit from Green Roofs?
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Additional information on green construction can be found at:
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Aside from the building’s reduced ecological footprint and cost-savings, green roofs are beneficial for providing a rich learning environment for students. The roofs become living laboratories and are perfect examples of sustainable design. And, perhaps most importantly, green roofs provide schools with an incredible power to increase environmental awareness and sensitivity.
Katrin Scholz-Barth was formerly the director of sustainable design for the HOK Planning Group, a business unit of The HOK Group Inc. Katrin is a national expert in green roof technology and leads efforts in ecological planning and design. She’s based in Washington, D.C. and can be reached at (202) 544-8453 or Katrin@Scholz-Barth.com.