A garland of nature crowns Chicago's City Hall, softening the hard edges of a town famous for steel and stone—and lowering summer temperatures on the roof. Inspired by a worldwide movement, Mayor Richard Daley has made Chicago North America's leading "green roofs" city.
A garland of nature crowns Chicago's City Hall, softening the hard edges of a town famous for steel and stone—and lowering summer temperatures on the roof. Inspired by a worldwide movement, Mayor Richard Daley has made Chicago North America's leading "green roofs" city.

Up on the Roof

A lofty idea is blossoming in cities around the world, where acres of potential green space lie overhead.

If buildings sprang up suddenly out of the ground like mushrooms, their rooftops would be covered with a layer of soil and plants.

That’s not how humans build, of course. Instead we scrape away the earth, erect the structure itself, and cap it with a rainproof, presumably forgettable, roof. It’s tempting to say that the roofscape of every city on this planet is a man-made desert, except that a desert is a living habitat. The truth is harsher. The urban roofscape is a little like hell—a lifeless place of bituminous surfaces, violent temperature contrasts, bitter winds, and an antipathy to water.

But step out through a hatch onto the roof of the Vancouver Public Library at Library Square—nine stories above downtown—and you’ll find yourself in a prairie, not an asphalt wasteland. Sinuous bands of fescues stream across the roof, planted not in flats or containers but into a special mix of soil on the roof. It’s a grassland in the sky. At ground level, this 20,000-square-foot garden—created in 1995 by landscape architect Cornelia H. Oberlander—would be striking enough. High above Vancouver, the effect is almost disorienting. When we go to the rooftops in cities, it’s usually to look out at the view. On top of the library, however, I can’t help feeling that I’m standing on the view—this unexpected thicket of green, blue, and brown grasses in the midst of so much glass and steel and concrete.

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