Gardens in the Sky
To Zach, Cynthia, and the Community Garden list:
Here is an excellent article about the increasing acceptance of
greenroofs and gardening on rooftops. Zach, I came to the Green Roofs
Conference at the Earth Pledge Foundatiuon last year. I am glad to see your
research being done on this worthwhile endeavor. I am part of a non-profit
group named ANPRC. (A New Perspective Restoration Company) Among other
goals, we have a vision of using organic hydroponic growing methods, along
with recycling food wastes with earthworms, (vermiculture) and then growing
more vegetables and herbs from the worm castings. Marketing the produce to
the same restaurants who supplied the food wastes will complete the
innovative project. I live in New Jersey and we are initiating some
projects locally. We would like to Collaborate with The EarthPledge
We have two support groups for growing food. To read archived postings,
or to subscribe to our Do-It-Yourself Greenhouse Development Group, go to
To read about and participate in a list for people who want to explore
non-exploitive methods of partnering and "doing business", please go to:
The OpenEco Collaboration Yahoo Group page can serve as another forum
for a discussion on this topic and project. You will find other articles of
interest on rooftop growing here.
Regards to all,
Peter J. Sullivan
Gardens in the Sky
by Claudia M. Lenart
Conscious Choice, July 2000
Despite the lure of our increasingly fast-paced cyber-existence, an ancient
undercurrent flows. People yearn to return to their green roots. In densely
populated urban centers, most of the green space has been paved over in
favor of concrete. But that hasn't stopped us. There are plenty of flat
rooftops, and this resource offers vast potential for greening our cities.
"I think rooftop gardening is going to become more popular as land becomes
more precious," says Liz Serritella, co-owner of Old Town Bed & Breakfast
and a new rooftop gardener. "I love to dig in the dirt. We had gardens
before, and when we moved I couldn't garden anymore," says Serritella. Last
spring, she put in two penthouse gardens to the delight of guests as well as
Serritella found that her rooftop gardens required an initial investment:
before installing a rooftop garden, gardeners need to check with an engineer
to ensure the structural safety of the roof. She also needed to install a
wooden deck and buy new lightweight containers for plants. And rooftop
gardening is trickier than ground level gardening, due to high winds,
sunnier conditions, and an increased need for water. But Serritella found
that there was a lot of information available on container gardening.
Lightweight planters and lightweight planting medium are readily available
at garden centers. One trick she learned from her research was to line the
containers with styrofoam, to insulate and help the plants over winter.
Rooftop gardens are definitely more complicated than digging a backyard
plot. But in areas where that backyard plot doesn't exist, they offer an
untapped potential for greening and cleaning up the air we breathe and the
peace that can be found communing with nature in a garden. They also offer
the exhilarating feeling of looking at the world from above.
"Flying into O'Hare, you see acres and acres of bare roofs. They all could
be green and that could make an enormous difference," says David Yocca,
principle of Conservation Design Forum, a landscape design group that
utilizes landscape architects, ecologists, and botanists to design
sustainable environments. Conservation Design Forum has been involved in
designing "new town" communities including Mill Creek in the far western
suburbs and Coffee Creek in Chesterton, Indiana, where the roof on one of
the community buildings will feature a putting green.
The firm also is in the process of greening up the 38,800 square-foot roof
at Chicago's City Hall, as part of a five-city U.S. Environmental Protection
Agency, Urban Heat Island Project, whose goal is to reduce smog by lowering
the temperature in congested cities.
The Chicago Plan
Just like dark clothes, dark rooftops absorb the sun's rays, heating
buildings and increasing temperatures in congested cities by as much as
eight degrees. Hotter buildings increase the use of air conditioning, which
leads to higher energy use and more pollution from the burning of fossil
fuels. Meanwhile, higher temperatures outside cook the pollution, creating
Other cities in the Urban Heat Island project, Baton Rouge, Louisiana;
Houston; Sacramento, California; and Salt Lake City, plan to use reflective
roof surfaces to deal with the problem. Chicago, however, has decided to
build an innovative "green" roof to reflect the sun's rays. Plants on the
roof will cool the air by evapotranspiration, a process in which plants
secrete water through their pores and as the water evaporates it cools the
air. Plants also take in carbon dioxide, release oxygen, and filter the air
to some extent. According to computer models conducted by the Lawrence
Berkeley National Lab, which is participating in the heat island project,
widespread use of reflective surfaces and green roofs could reduce summer
temperatures in cities by several degrees.
As Yocca points out, "the technology has been established for many years.
Green roofs are quite common in European countries, where they have had
problems with flooding." In fact, rooftop gardens aren't a new idea at all.
The first historical accounts of rooftop gardens date back to 500 B.C., when
the Hanging Gardens of Babylon were in place. During the Renaissance, Pope
Pius II had a roof garden built at his summer residence in Pienza, Italy. In
more recent history, settlers on the American Plains built sod houses to
insulate themselves from temperature extremes.
The technology that has made green roofs a realistic solution for today's
structures was developed in Germany, where some cities use them to combat
flooding problems caused by stormwater runoff. According to Theodore
Osmundson, landscape architect and author of Roof Gardens: History, Design &
Construction, 43 percent of German cities offer financial incentives for
building green roofs.
Green roofs are starting to catch on in the states, says Matt Carr, Garden
Roof product manager for American Hydro Tech, a company that manufactures
roofing membranes, including the one at City Hall. Three years ago, says
Carr, "we were working with two or three green roof jobs. Today, we're
overseeing about a hundred green roofs throughout the states. I think
Chicago is going to be one of the leaders in the country," Carr adds.
"They're really looking to green up the city."
Green roofs are a step forward from the old style of rooftop garden
associated with penthouses. Most of those rooftops feature a deck over the
roof and lots of large, lightweight containers that hold plants. While those
gardens are better than a bare black rooftop, they are high-maintenance
affairs that offer fewer environmental benefits than the newer green roofs.
The green roof planned for City Hall includes a seamless membrane made of
hot, rubberized asphalt designed to last the lifetime of the building. It
incorporates German irrigation technology, called a floradrain, which
retains water and reduces the need for irrigation of green roofs. During a
typical rainfall, this roof would retain 50 to 70 percent of the rainwater,
Next, a layer of gravel and lightweight soil will be spread in thicknesses
ranging from three to thirty inches. This will be planted with 20,000
plants, from shallow-rooted sedums and ivies to shrubs, hawthorn, and
crabapple trees, says Jessica Rio, spokesperson for Chicago's Department of
Environment. Many of the plant species will be of native origin, because
natives are hardier and can withstand adverse conditions like drought and
high winds. Most native prairie plants have root systems that are too deep
for roof gardens, but species that are found in hilltop prairies have
shallower root systems, says Yocca. Groundcover plants, including sedums,
mosses, and grasses can tolerate both an abundance and a scarcity of water.
"These plants will go dormant and turn brown during a prolonged drought, but
then they'll green up again as soon as it rains," says Yocca.
The roof won't be open to the public, but workers at City Hall and other
neighboring buildings will be able to enjoy the view from indoors. Local
scientists will enjoy a unique opportunity to monitor the effect of a green
garden on climate. Infrared satellite photos will also measure the
effectiveness of the green roof, and the black tar rooftop on the Cook
County building next door will serve as a standard for temperature
A green roof on top of City Hall is only part of the solution, of course.
The city intends to install other green roofs at strategic spots throughout
the city. But for rooftops to have any impact on reducing the city's
temperature, private building owners will need to follow the city's example.
City officials hope their innovation will start a trend. So does Yocca.
"People often think green roofs will cause problems. So it helps to have an
example," he says.
The city's green roof will cost about $1 million, which will come out of
funds the city won in a franchise lawsuit against ComEd. (The utility is
paying Chicago $25 million a year for four years.) Money from ComEd also
will be available in the form of grants for private building owners who want
to install a green roof or reflective roof surface. The city hopes these
grants will help inspire building owners to give it a go.
In fact, a green roof can be a relatively small-scale investment. The green
roof at City Hall is a large-scale undertaking known as intensive greening,
which includes areas of deep soil depth, a diversity of plants and a
park-like design. A smaller-scale version, known as extensive greening,
requires only a few inches of soil planted with low growing plants, such as
sedum. Carr says most of the projects he's seen have been intensive. But he
sees any green roof as an asset to the local environment. He expects more
new buildings, especially public buildings, will utilize green roofs as
government incentives become available.
Environmental benefits are the primary goal of roof greening. Green roofs
reduce stormwater runoff, insulate buildings leading to lower energy use,
clean the air, and control local climate, lessening the formation of smog.
But there are economic benefits, as well. Rio says the city expects to save
$4,000 per year in cooling and heating the building due to the insulating
capability of a green roof. In addition, the soil and plant cover on a green
roof protect the roof membrane from the elements, which leads to lower roof
maintenance and a longer lasting roof. "Green roofs can last fifty to a
hundred years as opposed to a fifteen-year roof," says Yocca. Rooftop
gardens can also add to the desirability of a building, allowing a property
owner to charge higher rents.
Green Roofs to Greenhouses
Rooftop gardens aren't the only option to green up rooftops. Roald
Gunderson, an architect who has worked on Biosphere II, promotes the use of
rooftop greenhouses. Gunderson has designed a sustainable, solar greenhouse
design for cold climates. Just like gardens, greenhouses get crowded out of
urban landscapes. But urban rooftops are more available and less expensive
than land at ground level. And rooftop greenhouses offer many of the same
benefits as rooftop gardens. While rooftop gardens clean the air outside,
greenhouses clean the air inside buildings. They also insulate buildings,
leading to lower energy use. "A solar rooftop greenhouse is actually more
insulative than a garden and is actually able to heat the building," says
One of the biggest advantages of a greenhouse is the production of locally
grown, organic food year round. "Chicago easily has about fifty square miles
of flat roof," says Gunderson. "Even ten square miles would offer a
tremendous opportunity for year round food production."
Gunderson also believes greenhouses provide an opportunity to bring the
outdoors inside, where we spend most of our time. "We spend 94 percent of
our time indoors, yet all things in a building are dead," says Gunderson.
"Greenhouses offer the potential to take us back to the human ecology we
lost... when we entered the industrial age."
"To be in a garden on a roof is the ultimate experience of being up high,
for here a garden is not supposed to be," says Osmundson. But rooftop
gardens can offer another high, as well: the satisfaction of being part of
the solution on a balmy summer day.
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