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The Chicago Botanic Garden won an award at this year's conference for its green roof.

Chicago tops the nation for green roofs

by Alan Yu
Oct 16, 2012


Green Roofs for Healthy Cities/Alan Yu/MEDILL

Green roofs are growing rapidly in North America.


Green Roofs for Healthy Cities/Alan Yu/MEDILL

Chicago has more green roofs than any city in the U.S.


Click on the map to see where you can find green roofs in downtown Chicago.

The “green roofs” industry kicks off its annual conference Wednesday in Chicago - the city that has more such environmentally friendly roofs than any other U.S. town.

At the four-day CitiesAlive conference, Toronto-based Green Roofs for Healthy Cities honors the most innovative green roof designs with awards of excellence. Attendees can also discuss trends and research in the fast-growing field. 

Green roofs are simply rooftops that make use of grass, flowers, decorative bushes and other plants on top of conventional building materials. That not only provides a more scenic environment, but can also yield locally grown food and reduce air-conditioning needs. And green roofs can help cities reduce the amount of water that spills into overloaded sewers during rainstorms. 

Thanks to such benefits, rooftop gardens have been sprouting across North America in recent years.  In 2011, the installation of green-roof square footage in North America  doubled to just over 16 million square feet, the industry group reports. Chicago is in the forefront of the movement thanks to strong backing from former Mayor Richard M. Daley. Chicago boasts more than 3.5 million square feet of green roofs, including a showcase roof on City Hall.

Despite their advantages, however, green roof backers face a difficulty. The problem? While the significant extra building cost they impose is easy to quantify, the benefits they provide are not as visible.

That’s why, in addition to celebrating growth, visitors at this year’s conference, sponsored by the Green Roof and Wall Industry Association, will be focusing on establishing building standards and metrics to gauge how well a green roof performs.

“We’re at the point where we’re working on performance standards to ensure long term growth,”said Steven Peck, president and founder of Green Roofs for Healthy Cities. “A lot of green roof push back has been associated with the upfront cost,” he said, “and our challenge is to research and quantify the benefits that you don’t really think about.”

Green roofs offer long-term savings  

Urban areas tend to be hotter than rural areas because paved concrete heats up much faster than soil or plants, leading to an increased need for air conditioning and other environmental stresses. Advocates  emphasize that green roofs can reduce the urban “heat island”effect, and some researchers have tried to put a dollar value on that benefit.

But plants on rooftops can save money for the humans living below, according to a 2009 study in New York City from a team that included Cynthia Rosenzweig at the NASA Goddard Institute for Space Studies as well as researchers from the Center for Climate Systems Research at Columbia University, Hunter College and other organizations.

The researchers set up green roofs and planted trees at buildings from Queens to the Bronx to find the most effective way of cooling urban heat islands.

The New York scientists found that although making buildings more reflective provides the greatest boost for energy efficiency, wide use of green roofs couldsave a total of more than $1 billion in power costs citywide over the course of 35 years.

Side effects from that strategy would include making the air cleaner, reducing polluted stormwater from running into rivers and curbing greenhouse gas emissions, their study found.

An aerial refuge for rare native plants

One of the awards that will be handed out at this year’s meeting will go to the green roof garden at the Chicago Botanic Garden. At the Glencoe facility, Kelly Ksiazek, a doctoral candidate for plant biology and conservation at Northwestern University, is studying  the way in which green roofs can support native plants and the birds and insects that pollinate them.

By comparing the growth of native plants on various green roofs across Chicago, she says, she has found that native plants grow on rooftops grow just as well as their ground-level counterparts.

“With the right maintenance and management, there’s no reason why green roofs can’t be habitats for some rare species,” Ksiazek said.

For example, she noted, limestone quarries are endangering the lakeside daisy by taking up its native prairie habitat, But the threatened daisy is now thriving atop the Chicago Botanic Garden. A separate study released this week by researchers at the University of Cincinnati also found that Ohio native plants fare better than other species on green roofs.

Why we don’t see more of them

Still, the expense of the environmentally friendly roofs isholding up adoption by some building owners, said Jeffrey Bruce, landscape architect and chairman of Green Roofs for Healthy Cities.

“The initial cost of green roofs tend to be an obstacle,” Bruce said. “If we can shift some of our thinking to life costs, it would behoove society to value the long term benefits.”

Bruce is among those who hope establishing performance standards and metrics will make it easier to compare  thebenefits and costs of a green roof. That process should take two to four years, estimates Peck. 

In a guide to rooftop gardening, the Daley administrationestimated that a green roof costs 50 percent more than a conventional roof.The city figures that the $1.5 million green roof installed in 2001 on top of Chicago’s City Hall saves $5,000 annually in energy costs.

In Chicago, landscape architecture best known for installing green roofs include  Conservation Design Forum, the company behind the City Hall roof; and Intrinsic Landscaping, the company behind the green roofs at O’Hare International Airport and Merchandise Mart.

Green roofs are more often found on commercial buildings, in part because the process for installing one on a residence isn’t easy. Cost is one factor, and in addition,homeowners need a building inspection to ensure the roof is strong enough, as well as regular maintenance said Ksiazek.

“Ideally a green roof should be saving you money in the long run as far as energy reduction,” she said, “but there are other benefits to a green roofthat a lot of people don’t see.”

It’s the same problem that the conference members will be discussing, she added. “Something like stormwater retention is really beneficial for the environment, but it might not be beneficial for your pocketbook.”