To make your building interesting and environmentally friendly, look no further than a green roof. A green roof is one that is substantially covered in vegetation. Green roofs have actually been around in one form or another for centuries; however, interest in them is just now “taking root” in the United States, where the demand for “green” buildings is growing and green roofs are the most visible indication that a building has gone “green.” Aside from the aesthetics, green roofs can

• Filter pollutants in the air. [1]
• Contribute to Leadership in Energy & Environmental Design (LEED) points.
• Create a habitat for wildlife.
• Extend the lifetime of a roof.
• Reduce the heat island effect. [2]
• Reduce heating and cooling bills.
• Help to insulate a building for sound. [3]
• Absorb carbon dioxide and release oxygen.
• Become healing gardens or herb and vegetable gardens.
• Turn an unattractive, unused space into a park-like setting.
• Become a source of income, by leasing the space out for events.
• Reduce storm water runoff and therefore decrease the size of a water retention pond.

Serve as a “green” alternative to traditional marketing media, by allowing marketing messages to be “written” on the roof in plants.

History and Construction

Green roof terminology came from Germany more than 100 years ago. For example, the Germans described roofs as intensive or extensive depending on their depth, just as we do today in the United States. Intensive roofs have growth media deeper than 6 inches, and extensive roofs have growth media shallower than 6 inches. Intensive roofs can therefore support a wider variety of plants, but they are heavier, require more maintenance, and are more expensive. Extensive roofs are covered in a shallower layer of growth media and vegetation, can require less maintenance, and are therefore less expensive. Green roofs traditionally have been applied in layers to form a monolithic green roof; however, in the last several years, modular systems such as the GreenGrid® Modular Green Roof System from Weston Solutions, Inc. have become popular. Modular systems are easier to install and facilitate easy rooftop repairs, when necessary, without damaging the green roof.

One of the major design considerations in a green roof system is its storm water retention capability to help mitigate flooding. For example, studies show that in a typical storm, the 4-inch-deep GreenGrid Modular Green Roof System reduces storm water runoff by approximately 75% of the first 1 inch of rainfall.

Asphalt parking lots and rooftops, in particular, retain heat and radiate it as thermal infrared radiation. The heat is released after sunset and forms a dome of higher temperatures over cities, which is called the heat island effect. This effect can cause temperatures in cities to be 6 to 10 degrees Fahrenheit above normal, changing weather patterns and forcing air conditioning systems to work harder and use more energy. This can intensify air pollution (ozone) and make living conditions uncomfortable. Green roofs are one of the best options for combating the heat island effect [2].

Green Roof Design Factors

Several factors need to be considered in designing a green roof. The weight, ranging from 18 to 22 pounds per square foot for an extensive roof and 30 pounds or more per square foot for an intensive roof, can be a significant consideration. Maintenance and irrigation options need to be considered in the choice of plants. The potential for high winds also needs to be factored into the design. In addition, if a building is applying for LEED credits, the depth and percent coverage of the roof should be considered.

A green roof can add quality to a building that cannot be accomplished any other way. Green roofs provide buildings with unique functional and aesthetic features. Like icing on a cake, a green roof tops off a building like nothing else can.

Green Roof Photographs

About the Author

Barbara Denson is the Director of Origination, Global Markets for Weston Solutions, Inc. (WESTON). Barbara graduated Magna Cum Laude in Civil Engineering from the University of Pittsburgh, where she was named “Outstanding Civil Engineering” student. Barbara began her professional career as an engineer for Amoco. She later owned and operated an oilfield services company. She then went overseas with her husband and resided in both Egypt and Bolivia, where she was chairwoman of Girl Scouting. Upon returning to the United States, she and her husband opened a business solutions company, which was the recipient of 14 national awards. Barbara has been a member of USA Today’s Small Business Advisory Committee and was on the Board of Directors of the Houston Chapter of the American Marketing Association, working to promote nonprofits. Barbara is actively involved in the green movement in Houston, participating in Scenic Houston’s Streetscape Committee, the Greater Houston Partnership’s Green Building Committee, the Gulf Coast Environmental Affairs Group, the Center for Houston’s Future and the United States Green Building Council.

Photgraphs and Images: Courtesy of Weston Solutions.

Footnotes

1. http://www.roofgreening.ca/content/AirQuality_Final.pdf
2. Reducing Urban Heat Islands: Compendium of Strategies – Heat Island Reduction Activities: Climate Protection Partnership Division in the U.S. Environmental Protection Agency’s Office of Atmospheric Programs
3. Reducing Urban Heat Islands: Compendium of Strategies – Green Roofs: Climate Protection Partnership Division in the U.S. Environmental Protection Agency’s Office of Atmospheric Programs, Green Roofs for Healthy Cities: About Green Roofs. www.greenroofs.org

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