REIDsteel Green Roofs
Modern urban roofscapes are lifeless places.
They experience violent temperature contrasts, bitter winds, and are an
antipathy to water.
However, a revelation in
roof design is securing itself a firm seat in the Sustainability club.
‘Green Roofs’ – gardens planted not into rooftop flower pots or
containers, but into a special mix of soil on the roofs – are becoming
more and more common. And not just for their beauty. Green Roofs lessen
the environmental extremes common on conventional roofs, reduce
storm-water runoff, increase energy efficiency, and enhance the urban
Waterproof membranes now make it easier to
design green-roof systems that capture water for irrigation, allow
drainage, support the growing medium, and resist the invasion of roots.
In some places, such as Portland, Oregon, builders are encouraged to
use ‘living roofs’ by fee reductions and other incentives. In
others—such as Germany, Switzerland, and Austria—living roofs are
required by law on roofs of suitable pitch.
During the summer, daytime temperatures on
conventional asphalt rooftops can be almost unbelievably high, peaking
above 150°F and contributing to the overall urban heat-island
effect—the tendency of cities to be warmer than the surrounding region.
On green roofs the soil mixture and vegetation act as insulation, and
temperatures fluctuate only mildly—hardly more than they would in a
park or garden—reducing heating and cooling costs in the buildings
below them by as much as 20 percent.
When rain falls on a conventional roof, it sheets off the city's
artificial cliffs and floods down its artificial canyons into storm
drains—unabsorbed, unfiltered, and nearly undeterred. A living roof
works the way a meadow does, absorbing water, filtering it, slowing it
down, even storing some of it for later use. That ultimately helps
reduce the threat of sewer overflows, extends the life of a city's
drain system, and returns cleaner water to the surrounding watershed.
London, for example, is already planning for a future that may well see
more street flooding, and the city is considering how living roofs
could moderate the threat.
The combination of soil, plants and trapped
layers of air within green roof systems can act as a sound insulation
barrier. Sound waves are absorbed, reflected or deflected. The growing
medium tends to block lower sound frequencies whilst the plants block
higher frequencies. Green roofs can reduce sound by 8dB compared with a
conventional roof system. This could be particularly important in areas
of high noise pollution such in the approaches to airports, as these
levels are sufficient to provide noise insulation to buildings under
aircraft flight paths.
naturally there are the environmental benefits. Plants absorb carbon
dioxide and release oxygen, and play an important role in minimising
Global Warming. These roofs are havens for wildlife. Species large and
small—ants, spiders, beetles, lapwings, plovers, crows—have taken up
occupancy on living roofs. And it's not just a matter of making new or
replacing existing habitat. In Zürich, Switzerland, the 95-year-old
living roof of a water-filtration system serves as a refuge for nine
species of native orchids eradicated from the surrounding countryside
when their meadow habitat was converted to cropland.
While the average cost of installing a green
roof can run two or three times more than a conventional roof, it's
likely to be cheaper in the long run, thanks largely to energy savings.
Vegetation also shields the roof from ultraviolet radiation, extending
its life. Maintenance extends to some light gardening every now and
Stephan Brenneisen, a Swiss scientist and a
strong advocate for the biodiversity potential of living roofs, says
simply, "I have to find easy, cheap solutions using materials that come
from the region." That means less reliance on plastics and other
energy-intensive materials between the roof structure and the plants
themselves. What matters isn't only whether living roofs work. It's how
to make them work in the most sustainable way, using the least energy
while creating the greatest benefit for the human and nonhuman habitat.
Green Roofs are adding habitat to cities,
filtering rain, moderating temperatures. And in a World where humans
have robbed it of its resources, hunted its wildlife, and poisoned its
atmosphere, people will feel much happier in a building that has given
something back to Nature.
Read 'The Whole Story' which looks at
the whole lifecycle of sustainable built environments.