Chicago's Enironmentalists Hit the Roof
When a team of scientists swooped in over downtown Chicago last year aboard a police chopper, they noticed something astounding: the black asphalt roof atop the county building that adjoined City Hall measured in at 150 degrees Fahrenheit.
Armed with thermal imaging cameras, the scientists and environmentalists then shifted their equipment to City Hall’s “green roof” – a roof covered in lush vegetation. That roof, they noted, was cooling out at a mere 70 degrees.
“It really confirmed a lot of what we knew” about green roofs, says Sadhu Johnston, chief environmental officer in the Chicago mayor’s office.
Indeed, the massive discrepancy highlighted just how effective green roofs can be in combating the urban heat island effect, which plagues many large U.S. cities.
A heat island is an urban area that is significantly hotter than its surroundings. The condition is due in large part to the modification of a city’s land surface with materials like concrete and asphalt. To combat this problem, and others, cities across the U.S. ( and around the world), are turning to green roofs.
Spurred by its active mayor, Richard M. Daley, who has enthusiastically promoted the creation of green roofs all over the city, Chicago today boasts between 450 and 500 of them -- either currently in place or under development. They cover some 4.5 to 5 million square feet—more than any other city in the United States and, very likely, the world.
The roof on Chicago City Hall includes over 25,000 square feet of vegetation, and more than 150 different varieties of plants, mainly adapted and indigenous prairie plants.
Chicago has developed a series of programs to get the private sector on board with green building initiatives. Among these efforts, the city now offers tax increment financing for green building projects.
“If you’re interacting with us [on a building project], we’ll require that you implement green strategies in you’re constructions—and we’ll require different ones for different projects,” Johnston says. “For big boxes, commercial properties, green roofs are the way to go.”
The heat island effect isn’t the only problem green roofs are solving. They also help address cities’ lack of green space, as well as difficulties retaining storm water. Chicago , for example, has a combined sewer overflow system; in a storm, raw sewage flows into the river. The vegetation on green roofs helps retain rain water.
“We did our first green roof in 2000, which was on City Hall,” Johnston says. “That was the first on a municipal building in the country as far as we know.”
Later, the city began building green roofs on other buildings—schools, fire stations, museums. Today, they sit atop municipal and corporate buildings, along with private homes. There’s even a green roof on a local McDonald’s restaurant.
The actual growing medium, on City Hall and elsewhere, tends to be some “recipe” of inorganic material, says Michael Berkshire, green projects administrator at the Department of Planning and Development. This sort of material usually is a good deal lighter than soil (which takes pressure off the roofs), and retains water well.
“A rooftop is a piece of real estate that typically goes unused, and it’s a very valuable piece of real estate, especially in a city like Chicago ,” Berkshire says.
Mayor Daley, he adds, is “very committed to it and also very passionate about it.”
“He understands not only the environmental benefits of green roofs, but also the aesthetic value of a green roof,” Berkshire says. “People who live in high-rises, their roof top is their landscape. It really adds value to your view.”
