Plants, grass on the rooftop? No longer an oddity.

In the center of downtown Chicago lies an oasis of green.

Monarch butterflies flit past little bluestem. Bees fly from prairie clover to purple coneflowers. A small hawthorn tree rises from a mound.

The expanse of native plants and grasses isn't a park, but the top of City Hall, the premier green roof in a city that is making green building a civic cornerstone.

Six years ago, when Mayor Richard Daley had the roof installed, it was an oddity. Today, more than 200 green roofs in the city have been constructed or are under way, covering some 2-1/2 million square feet of tar with plants – by far the most of any American city.

Now other cities, hoping to cool and clean their air and help with storm drainage, are beginning to emulate Chicago, and the city is taking key steps to encourage – and in some cases require – private developers to follow City Hall's example.

Chicago's City Council just announced a pilot program that will provide up to $100,000 in matching funds for developers who retrofit existing downtown buildings with green roofs, out of a $500,000 pool of financing. Last year, the city began awarding small $5,000 grants to smaller projects, many residential. A green permitting process is designed to expedite requests. And Chicago has started requiring green roofs on new buildings that receive city financing.

"You look down on the prime real estate areas of this country – downtown Chicago, Manhattan – and so much is unutilized, all these rooftops," says Sadhu Johnston, Chicago's environment commissioner. The green-roof push, he says, is just one piece of a larger plan for the city that has included adding hundreds of thousands of trees, increasing energy efficiency, and replacing some traffic lanes with planted medians. "It's about a comprehensive strategy of making Chicago a better place to live."

Green roofs may be surprising in a city still more known for manufacturing than composting, but they are relatively common in Europe. Germany – the country that gave Mayor Daley the idea – has green roofs on about 20 percent of all flat roofs, according to one estimate. With a history dating back to the hanging gardens of Babylon, green roofs range from simple trays filled with hardy plants like sedum, to complex systems like the City Hall roof, which features some 150 plant species, a small apiary, and two trees.

In Chicago, they sit atop the Apple store, a Target, and a McDonald's. Even Chicago's soon-to-open Wal-Mart will have one – the company's first.

Nationally, green roofs grace the Gap headquarters in San Bruno, Calif.; a Ford Motor plant in Dearborn, Mich.; and the American Society of Landscape Architects building in Washington.

Page: 1 | 2