New York Living
The Emerald City
A visionary group plans a lush new urban landscape
Every year, 3.5 million visitors travel more than 1,000 feet up to look out
on a sea of city rooftops from the observation deck of the Empire State Building. If Leslie
Hoffman has her way, instead of black and brown roofs, those tourists will soon be seeing a
sea of green. “Just think about what a wasted resource all that rooftop space in New York
is,” says Hoffman. “Here’s an opportunity to bring nature, open space, and biodiversity
habitat into our lives using a wasted resource.”
Hoffman’s sea of green consists of “green roofs” on almost every building. More than just a
garden up on the roof, a green roof–or “eco roof”–makes the garden a part of the building.
The garden rests on a structure built to handle the weight of plants, dirt, and water–and to
use these elements to do the job normally reserved for a layer of asphalt. Hoffman has
installed a green roof above Earth Pledge’s East Side townhouse. Besides the fresh-grown
tomatoes, squash, and herbs just a few stair steps away, green roofs are recreational
space. “You can do a little bit of gardening, or just have some experience of grass,” says
Jane Kenny, regional director of the Environmental Protection Agency. “Even is you’re in
another building and you’re looking down on green roofs, it gives you a little bit of peace.”
Hoffman’s motivation is the environmental benefits the roofs promise. As the executive
director of Earth Pledge, an environmental group that calls the New York region its
“laboratory,” she is involved with everything from promoting organic produce from the
Catskills to advocating the transformation of city trash into clean energy. Hoffman’s
initiatives are accompanied by lots of press, and she gets results. More than 250 farms have
joined her project, called Farm to Table. Hoffman also recently won funding to install the
first small-scale “digesters” at three New York sites, including two high schools. Functioning
like giant stomachs-in-atank, the digesters take in waste and turn out energy.
For her organization’s greenroof initiative, Hoffman has enlisted support from a wide range
of public faces. Actor Ed Norton, Mayor Michael Bloomberg, Councilman Gifford Miller, Prada
model Angela Lindvall, and activist Robert Kennedy, Jr. have all signed on to what Hoffman
calls “Greening Gotham.” “We’re supporting green roofs because they provide so many
important benefits to people and to the environment,” says the EPA’s Kenny. “They also are
economically viable,” she adds, noting a study that showed green roofs can reduce
air-conditioning costs by 20 percent.
Do the rooftop gardens of Rockefeller Center, built in the 1930’s, serve as an early
prototype for the green roofs Hoffman envisions for New York City? “They do in a certain
regard and they don’t in another,” says Hoffman. “Those are not a lightweight engineered
system with the layers we are advocating. On the other hand, they do capture storm water,
and they do cool the air, and they do create beauty.”
The advantage of the new greenroofing systems is that they are light enough to be installed
on buildings that were not built to support the weight of dirt, water, and plants. President
David A. Caputo of Pace University is planning a green roof at his university’s building on
One Pace Plaza in lower Manhattan. “I hope we would be dedicating this within two or three
years,” Caputo says.
The Calhoun School on the Upper West Side is also planning a green roof. To maximize the
benefi t, Hoffman is developing curricula for the school. “Biology classes will study by doing
Mendel pea experiments,” she says.
Builders broke ground in December on a new home for South Bronx grandparents who are
raising their grandchildren; the building’s green roof will be welcome in a neighborhood with
few parks. “This is going to be a private, safe green space for children, as well as an
improvement of the environment in the South Bronx, where 25 percent of the kids have
asthma,” says Hoffman.
It may be tempting, but you shouldn’t try to create a green roof of your own without expert
help. A mistake could lead to leaks or having the “green” fall through the “roof.” First
consult with companies such as American Hydrotech, which is creating a 20,000 square-foot
green roof on the St. Georges Ferry Terminal on Staten Island.
A green roof can best be seen as a layer cake. The first layer is the waterproof barrier. An
optional layer of insulation is next. The drainage layer can be as simple as a bunch of
pebbles. To keep the dirt out of the pebbles, a layer of polyester fi ber fabric goes down
The soil mixture used on green roofs usually consists mostly of inorganic ingredients like
crushed clay or expanded slate–“puffed stone” in Hoffman’s words. About one-third is
organic matter such as humus and top soil. The icing on the cake is the vegetation. What
you choose depends on how much time you want to spend gardening and the look you
want. Do you want fruits and vegetables or fl owers? Shade trees or prairie grass?
For her roof, Hoffman has chosen plants that draw what many New Yorkers would call
unwelcome guests. “Our roof buzzes with pollinators all summer long,” Hoffman says,
referring to bees, dragonflies, butterflies, and moths. To Hoffman, there are too few of
these flying around. “We are in a pollinator crisis in this country,” she says. “The pollinators
have basically been dying,” due to pollution, pesticides, habitat loss, and other scourges of
the natural environment. She hopes that green on the rooftops of the five boroughs will
contribute to a resurgence of the creatures that make possible flowers to berries, herbs, and
Hoffman is serious about the pollinator crises, but it is down on the list of ecological
disasters motivating green “roofies.” In New York, first on the list is water, or, more
The city mixes roof runoff with the water that we flush down our sinks, tubs, and toilets.
Every time it rains, the extra runoff causes the treatment system to overflow. As a result,
40 billion gallons of wastewater, including raw sewage, pours into our rivers and harbor
Green roofs absorb water; asphalt and other city roofs chute it into a pipe, where it adds to
the problem. “A typical green roof can certainly carry an inch or an inch and a half of rain,”
Hoffman says. “And 88 percent of New York City’s storm events are of an inch or less.” A
network of green roofs in New York could reduce sewage overflow.
And that’s not all green roofs could do. Asphalt and brick streets, buildings, and roofs make
the city as much as 5.4 degrees Fahrenheit warmer than New Jersey or Long Island. The
city absorbs heat each day and releases it at night. It gets hotter as the summer drags on.
This makes Manhattan a “heat island” that shows up on satellite thermal images as a bright
red and yellow blob. The heat-island effect means more air conditioners on, more energy
being used, more smog-causing ozone hanging over the city, and more New Yorkers
developing asthma. Green roofs could impact the city by cutting energy bills for individuals
and buildings, cooling the heat island, and curtailing emission of greenhouse gases.
Progress is being made. A new apartment building in Battery Park City called the Solaire has
two green roofs. “I’d like to look down, flying over New York, and see a second Central Park
made up of rooftop gardens,” says Diana Balmori of Balmori Associates Inc., the architect
who created Solaire’s green roofs. According to figures provided by Hoffman, Balmori may
be underestimating the possibilities. In all, Hoffman said, about a fifth of New York is
covered with the flat roofs that may be suitable for greening. In Manhattan, the 386,000
existing flat roofs offer a combined 21,249 acres of potential green space.
By comparison, Central Park is 843 acres in size. Greening the roofs of Manhattan would
add at least 457 more Central Park’s worth of greenery to our city, providing welcoming
landing stations for migratory birds and native species. Energy bills would be lower, the
water and air cleaner. In Hoffman’s New York, instead of being the paved, hot center, the
city would become a relatively cool, lush oasis.