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Building and operating facilities that are environmentally responsible is on everyone’s mind in schools and hospitals throughout North America. Many are taking environmental issues very seriously and are retrofitting or building entirely new structures to meet LEED® (Leadership in Energy and Environmental Design) certification and standards.

Although roofs have been long overlooked, facility managers are taking a closer view even here to see how they can make them more environmentally preferable, last longer, reduce stormwater runoff and save energy for the entire facility. Although this is a burgeoning trend in the United States, the concept of installing Green roofs is not exactly a new one.

Green roofs originated centuries ago in parts of Europe where other roofing and construction materials were not available. A millennium ago, sod houses were built in Iceland, Greenland and even Newfoundland sporting vegetation atop the roof. Early North American settlers were known to build roofs or entire houses of sod. And it was not uncommon at that time to see the homeowner chase away goats grazing atop the roof.

Although sod houses and structures are no longer practical, Green roofs have lived on. For more than three decades, German developers and property owners have been installing Green roofing systems atop new and existing structures. Today, more than 10 million square feet of Green roofs are installed annually in Germany and the market has been growing at a steady clip of around 10 percent every year.

Because of their growing interest, hospital and school administrators considering the installation of a Green roofing system should know what are now considered the key benefits of a Green roof system. Additionally, such issues as costs to install a Green roof and the short- and long- term maintenance of the Green roof should be understood as well.

Key Benefits
Before even considering the addition of a Green roof, it is important to know the carrying capacity of the existing roof. An extensive Green roof fully saturated can weigh ten to 28 pounds per square foot. A licensed professional can help determine whether a roof can support this much added weight.

Once it is clear the building can support a Green roof, facility managers can consider the benefits. For instance, Green roofs help quiet structures, provide a habitat for wildlife and turn rooftops into a refuge for building occupants. However, the three benefits that are now or are becoming key factors involve the Green roof’s ability to manage stormwater runoff, reduce energy costs and extend the life of an existing roof.

Stormwater Runoff
What has long been identified as the significant benefit of a Green roof is how effectively it can address the problem of stormwater management. With an extensive Green roof—the most common Green roof installation involving three to eight inches of soil in which growth media (soil) is planted—the U.S. Environmental Protection Agency estimates that after one-half inch of precipitation, at least 75 percent is absorbed by the Green roof. Other studies indicate more than 90 percent is absorbed by the Green roof.

Why is this a key benefit? Stormwater, as it leaves building rooftops gathers pollutants, chemicals, bacteria and other contaminants, flowing directly onto city streets and sidewalks. After a major rainfall event local water treatment facilities may be unable to handle the load, resulting in significant amounts being dumped directly into waterways, affecting the health of aquatic life and other living things. Additionally, stormwater management systems are coming under much greater scrutiny resulting in the implementation of new regulations and standards for building developers that are adding to the costs of new construction.

Energy Conservation
Another significant benefit of Green roofs is the role they play in energy conservation. The precipitation absorbed by the Green roof after a rainfall event is slowly released into the atmosphere. This helps cool surrounding areas and helps reduce the “urban heat island” effect that makes downtown areas so much hotter than surrounding forested areas. And because the existing roof is covered by soil and vegetation it remains relatively cool throughout the year. When it is 80 degrees Fahrenheit outside a conventional roof can be as hot as 180 degrees; a Green roof reduces this significantly.

According to studies conducted by the University of Toronto, Green roofs can help save as much as 6 percent in facility energy costs during a typical summer, if not more. Other studies report that the demand for power, mostly to air-condition facilities increases 3 percent with every half degree increase in temperature. But by reducing the urban heat island effect this rise in temperature can be moderated. In fact, just a one- degree reduction in the urban heat island effect can decrease the demand for electricity to air-condition buildings by as much as 5 percent.

Increasing the Life Span of the Existing Roof
Most new roofs are designed to last at least twenty years. However, when they need to be replaced, installation can prove to be very costly as well as disruptive for building users. Green roofs, as referenced earlier protect the existing roof from temperature extremes and it is these temperature extremes that cause the roof to wear and crack.

The vegetation also helps protect the roof from ultraviolet radiation and other climactic stresses. According to David Beattie, professor of ornamental horticulture at Penn State University, “A black surface roof can get extremely hot during the day and then cool more than 100 degrees at night. [This causes] the roof’s membrane to expand and contract and after a while the [roofing] material tends to fatigue and break up. But a Green roof moderates those temperature extremes so the life of the roof might be extended two or three times.”

Indeed, it is now commonly believed that a Green roof doubles the life expectancy of the existing roof. Instead of dealing with a major roof installation costing thousands of dollars every twenty years those same funds can be used for other projects that benefit students or patients.

Costs
Green roofs tend to cost more in the U.S. than in Europe. Part of this is because Europeans have had more experience installing Green roofs and the technology is still relatively new in this country. Prices can vary depending on a host of factors, such as:
• The type of existing roof where the Green roof will be installed
• Permits and fees
• Hourly labor charges in your locality
• Costs of plants, soil and drainage systems
• Transporting the Green roof materials to the job site

However, new Green roof technologies are being introduced that are addressing many of these issues and helping to lower costs. For instance, installing the Green roof atop Chicago’s City Hall in 2001 proved to be a major learning experience for the industry. Typically, Green roofs are built with crews working directly on top of the existing roof as it was on City Hall. However, this proved to be a costly challenge on the near one-hundred-year-old building.

After that installation one of the technologies engineers developed was a modular Green roof system. With the modular system the Green roof (soil and growth media) is preplanted in square or rectangular modules made of recycled plastic and then placed on the existing roof. The installation is relatively fast, less costly and labor intensive and has allowed more facilities to take advantage of Green roofing systems.

Maintenance Issues
Northwestern University is about to open Prentiss Women’s Hospital in Chicago. The state-of-the-art facility hopes to be LEED certified shortly after opening and among other Green features, includes a Green roof.

However, before installing the Green roof the hospital installed a “pilot” Green roof on an existing building. One of the chief concerns is the maintenance requirements of the roof. Although the vegetation was changed shortly after installation in response to requests for a more colorful setting by patients and staff of surrounding buildings that could look out on the Green roof, the roof has required essentially no maintenance whatsoever according to the project administrator.

The hospital which installed a Green roof system as described earlier did have the installers water the roof once in place and prune and weed as necessary. However, after the initial installation no further attention was needed.

When it comes to maintenance facility managers should know that plant selection is vitally important to the survival of the Green roof. The conditions atop a roof with more sunlight, wind and heat exposure can be much more intense than at ground level. The plants selected must be hearty, drought-tolerant and native to the local environment.

Selection of growth media is also crucial. Engineered soil is a new technology that has helped Green roofs grow with little or no maintenance. Considered the foundation of the Green roof, the soil is mixed with specific chemicals and nutrients to help the plants live after the initial installation as well as over the long term.

With benefits of Green roofs mounting, costs coming down and maintenance issues negligible the prediction is that more schools and hospitals will be installing Green roofing systems. “I have found that Green roofs serve another important role as well,” says Jim Lindell with GreenGrid® , a manufacturer of Green roofing systems. “The plants and vegetation remind us that we can take steps now to help us better care for our planet in the future.”

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