Green rooftop technology saves energy, cools air

[Paul R.]

http://www.cnn.com/2001/NATURE/01/01/rooftop.gardens.enn/index.html

Green rooftop technology saves energy, cools air

                  January 1, 2001
                  Web posted at: 12:01 p.m. EST (1701
                  GMT)

                  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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                  RELATED SITES:

                       City of Chicago
                       Heat Island Group
                       Green Roofs for Healthy Cities
                       Greenroofs.com
                       Urban Agrigulture Notes
                       Rooftop Gardens Resource Group