the VOA Special English Development Report.
roofs are designed to save energy and capture rainwater. Rooftops covered with
plants help keep buildings cool. They can extend the life of a roof. And they
can reduce water runoff into streets and storm water systems.
years ago, the mayor of Chicago, Illinois, visited Germany, a leader in green
roof design. Mayor Richard Daley later decided to have vegetation planted on
Chicago City Hall. Today, the tops of many other buildings also look like
Canada, the Coast Plaza Hotel in Vancouver has a forest on its roof.
say green roofs usually do not get much above twenty-seven degrees Celsius. So
temperatures might not be a problem for growing. But rooftop gardeners have to
be careful not to put too much weight on the roof. This is true whether plants
are grown in soil or water.
City has an unusual demonstration farm for hydroponics. The farm is on a boat
called the Science Barge. Rainwater and purified river water are used to grow
lettuce, tomatoes, cucumbers and peppers. The farm shows the possibilities for
designing rooftop systems.
this year, researchers in Texas reported that green roofs can reduce a
building's air conditioning costs by about one-fifth compared to black-top
roofs. But they also reported that not all green roofs perform equally well.
They found that designs differ in their ability to keep buildings cool and to
Simmons led the study for the Lady Bird Johnson Wildflower Center at the
University of Texas at Austin. "Green roofs have to be done right,"
he says. For example, he says, "Just having a green roof may not mean
anything in terms of preventing water from reaching the street level."
put experimental roofs on top of metal insulated boxes, to recreate green roof
conditions. The study compared products from six companies. The researchers say
they want to help businesses understand how to improve their designs.
rooftop had sixteen different kinds of plants native to Texas. The researchers
say the presence of native plants likely helped all the green roofs capture
water better compared to sedums. Sedums are plants that need little water and
often are used on green roofs.
native plants could take in more water and release more of it to the
that's the VOA Special English Development Report, written by Jerilyn Watson.