Green rooftop technology saves energy, cools air

Residents of overheated cities such as Chicago are trying to cut cooling costs with rooftop gardens

By Environmental News Network staff

During the summer months, the temperature of a conventional flat rooftop can soar up to 140 degrees Fahrenheit - hot enough to fry an egg.

This heat creates tremendous updrafts, circulating tiny particles that can clog lungs. The additional heat increases the need for electricity production, which further adds to air pollution.

By contrast, a grass rooftop can't get any hotter than about 77 degrees. This innovative technology can help relieve city smog and cut energy consumption. With enough green roofs, the temperature of a entire city can decrease.

A 3- to 7-degree temperature drop translates to a 10 percent reduction in air conditioning requirements. For a one-story structure with a green rooftop, cooling costs can be cut by 20 percent to 30 percent.

A recent study done by Weston Design Consultants for the city of Chicago estimates that the greening of all of the city's rooftops would produce $100,000,000 in saved energy annually. Peak demand would be cut by 720 megawatts - the equivalent energy consumption of several coal-fired generating stations or one small nuclear power plant.

Green rooftops offer other environmental benefits. They capture and filter air pollutants and retain as much as 50 percent to 70 percent of the storm water that they capture. This reduces storm water contamination and the risk of flooding.

Green rooftop technology replaces traditional flat rooftops with a series of carefully engineered layers. A water- and root-repellent membrane is installed on top of a reinforced roof structure. A drainage layer separates growing material from the underlying membrane.

A filter cloth keeps the drainage layer from getting plugged by the growing medium, which constitutes the top layer. This growing medium is designed to be as light as possible and still support plant growth.

Significant long-term savings can offset the cost of installing a green rooftop. Green rooftops last twice as long as standard roofs, reducing maintenance and replacement costs. They also muffle sound, creating a more efficient work environment.

Green rooftop technology is just being introduced in the United States and Canada, but it is a common feature of construction in Germany, France, Austria, Norway, Switzerland and other European countries.

In North America, cities such as Chicago and Toronto have established green rooftop demonstration projects on city-owned buildings. Washington, D.C., and Portland have begun to conduct research on the benefits of public green rooftops.

Copyright 2000, Environmental News Network, All Rights Reserved

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Green Roofs for Healthy Cities
Greenroofs.com
Urban Agrigulture Notes
Rooftop Gardens Resource Group

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