June/July
2004
New Urban Pastures:
The Promise of Green Roofs
By Stephanie Miller
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Ford
Motor Company’s green roof in Dearborn, MI |
Three and a half degrees. It doesn’t
seem like much, but it can save energy and resources, help the environment,
and improve our quality of life. Most cities are 3.6 to 5.4°F warmer
than surrounding areas, and green roofs (also known as ‘eco roofs’
or ‘vegetated roofs’) can reduce this ‘urban heat
island’ effect. Reducing the temperature of a building reduces
the amount of energy needed to cool it, saving money and resources—and
this is only one of the many benefits green roofs provide.
More than Pretty Planters
Green roofs are not simply the pots of flowers or landscaped gardens
that most of us have seen atop tall buildings. Rather, the name indicates
a sophisticated system of layers of barrier membranes, soil, and plants
on top of a traditional roof. Colin Cheney, Director of Green Roof Initiatives
for the NYC-based nonprofit Earth Pledge, confirmed that the two greatest
misconceptions about green roofs are that they are, “a lot of
heavy, wet soil that will make [an existing roof] collapse, or a collection
of terra cotta planters.” To counter this misunderstanding, Cheney
emphasizes that the two most important elements to remember about green
roofs are that they protect the underlying roof and that they are specifically
designed to support plant growth while remaining lightweight.
Green roofs may be designed as gardens that accommodate visitors, or
they may not. What they do support is cooler buildings, storm water
runoff mediation to take stress off of urban sewer systems, and enhanced
habitats for insects and birds.
Hot Enough for You?
A flat, black tar rooftop can get as hot as 185°F on a summer afternoon,
while the same roof, vegetated, would register a mere 75°F. While
the green roof results in direct energy savings for the individual building
owner, it also contributes to the reduction of overall energy consumption.
A critical mass of green roofs will directly affect the energy consumption
of an entire community.
Stormy Weather
We are all aware of the detrimental effects of acid rain, but most of
us don’t understand what normal or heavy rainfall does to a city’s
infrastructure. In New York, storm water runs off of the rooftops and
other impervious surfaces (sidewalks and streets) and directly into
the sewers. During heavy rains, the system is overburdened and often
raw sewage and rain mix and run directly into our waterways. Green roofs
can relieve this problem by absorbing up to 75 percent of rainwater,
significantly diminishing the amount that runs into the sewers, helping
control what can be a damaging and dangerous situation. Storm water
runoff has also been identified as a contributor to water pollution,
since it contains heavy metals and toxins carried from rooftops and
sidewalks. Limiting this runoff will prevent these dangerous pollutants
from passing into our waterways.
Looking for Leadership
Americans are just now catching on to what has been well established
in other parts of the world for years. According to Earth Pledge, approximately
10 percent of Germany’s buildings now sport green roofs and Tokyo
has mandated that useable space atop new buildings larger than 1,000
square meters must feature at least 20 percent green roof. The city
of Toronto has even capped its City Hall with an experimental green
roof that is open to the public.
Portland, Oregon, has been supporting eco roof projects since 1994,
driven in large part by concern over storm water runoff. Unlike New
York and other cities, Portland charges building owners a storm water
runoff fee in addition to the one charged for sanitary sewer service.
As an incentive, Portland set up a bonus program: developers are able
to include extra floor area in a new building if a green roof is installed.
The city also offers technical assistance and has helped finance several
projects. The green roofs reduce the amount of storm water runoff and
save the building owners money—a classic ‘win-win’
situation for individuals and the greater community.
Green Roofs = Greenbacks
Colin Cheney believes that cost is still the greatest obstacle to implementation
of green roofs in New York City. While many different sectors, from
private developers to the City government, have expressed interest,
the technology is still new enough everywhere in the U.S. that there
is a lag between product development and the education and experience
of local professionals in the market. Cheney indicated that, Earth Pledge
“is helping to spur the local industry, to bring [green roof]
projects to qualified professionals.”
One reason that green roofs have taken off in cities like Portland is
the significant support they receive from city government. Earth Pledge
is currently in conversation with the City Council and other public
agencies to explore the potential for economic incentives tied to green
roofs.
So what do these projects really cost? A number of variables are involved,
including the depth of the growing medium (anywhere from two to six
inches), the type of vegetation, if they will be accessible to people,
whether or not an irrigation system is installed, and more. Costs typically
range from $9 to $40 per square foot.
Notable Examples
In June 2003 the Ford Motor Company installed the largest green roof
in the world on top of a truck assembly plant in Dearborn, MI. The 10.4
acre green roof is covered with sedum, a drought-resistant plant, and
can absorb up to four million gallons of rainwater each year.
Other notable green roof projects around North America include:
• Chicago City Hall: A 20,000 square foot green roof that was
developed as part of the city’s ‘Urban Heat Island Initiative.’
• Toronto City Hall: Installed in 2000 as part of the Green Roof
Infrastructure Demonstration Project, it is open to the public during
the day.
• 20 River Terrace: This New York City residential skyscraper
is currently under construction in Battery Park City and will include
a green roof along with a variety of other sustainable design elements.
Ensuring a Greener Future
Earth Pledge, in conjunction with Columbia University, has embarked
upon a multiple-year study entitled the New York Ecological Infrastructure
Study. Launched in November 2002, the study aims to provide a preliminary
analysis of environmental issues particular to New York City to understand
how green roofs can help address them. A preliminary report will be
issued in late summer or early fall.
Whether reducing temperatures, fostering biodiversity by providing a
home for myriad birds and insects, or mediating the damage done by storm
water runoff, green roofs are clearly an idea whose time has come.
Stephanie Miller is a Consulting Editor of Satya.
To learn more about green roofs, check out these resources: Earth Pledge
(www.earthpledge.org;
212-725-6611), www.greenroofs.com,
and Canada’s Cardinal Group (www.greenroofs.ca).
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