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.
Living roofs aren't new. They were common among sod houses on the American prairie, and roofs of turf can still be found on log houses and sheds in northern Europe. But in recent decades, architects, builders, and city planners all across the planet have begun turning to green roofs not for their beauty—almost an afterthought—but for their practicality, their ability to mitigate the environmental extremes common on conventional roofs.
Across town from the library, the Vancouver Convention Centre is getting a new living roof. Just across the street there is a chef's garden on the roof of the Fairmont Waterfront hotel. Across town in another direction, green roofs will go up on an Olympic village being built for the 2010 Winter Olympics. To stand on a green roof in Vancouver—or Chicago or Stuttgart or Singapore or Tokyo—is to glimpse how different the roof scapes of our cities might look and to wonder, Why haven't we always built this way?
Technology is only partly the reason. Waterproof membranes now make it easier to design green-roof systems that capture water for irrigation, allow drainage, support the growing medium, and resist the invasion of roots. In some places, such as Portland, Oregon, builders are encouraged to use living roofs by fee reductions and other incentives. In others—such as Germany, Switzerland, and Austria—living roofs are required by law on roofs of suitable pitch.
And, increasingly, researchers such as Maureen Connelly—who runs a green-roof lab at the British Columbia Institute of Technology—are studying the practical benefits green roofs offer, helping quantify how they perform and providing an accurate measure of their ability to reduce storm-water runoff, increase energy efficiency, and enhance the urban soundscape. There is beginning to be a critical mass of green roofs around the world, each one an experiment in itself. There's more here.
But what about us? A couple of floors above us there's a sizeable rooftop terrace where air conditioning units hum, bats and swallows squeak overhead, the occasional cricket and butterfly swings by, and which we and our neighbours only visit to dry our washing and (in our case) water the half dozen shrubs, rose bushes and fruit trees that we don't have room for in our flat. Perhaps some kind of green roof might be practical up there?
I don't know that it would have a major impact on power use because, although this building is cold in winter and hot in the summer, so we all need heaters and air conditioners, that's probably more to do with the full-height external wall than heat transfer through the roof. And we couldn't use the whole roof because we do need to be able to dry our washing.
But in a modest neighborhood experiment, we might be able to convert an exposed, under-used roof into a fairly low-maintenance green space that gives everyone the pleasures of a garden in our brick and concrete environment, and incidentally provides a weather shield for the original surface.
Of course, we aren't a big architectural practice factoring planning regulations into a major project; or a big company with 6,000 square feet of roof space, and tax-deductable green ideas. We're private tenants in an apartment block. And there's a recession on. (Uhuh..) So I'm talking not much expertise, not a lot of spare time, and even less spare cash. But you can establish a green roof on a limited budget.
Our small apartment building has plant pots on every landing and most windowsills; and neighbours who talk to each other - often about who's growing what (a fern, geraniums, spider plants, aloe vera), where (sunny landing, shady corner), and how (staking, watering, neglecting). And so, perhaps, if we get together, and do our homework, we might be able to come up with something we can afford and maintain, and whose merits would convince that cautious breed, the landlord.
In the meantime, according to the IGRA (International Green Roof Association) website, the largest Green Roof project in world is just outside Madrid. It was -5C here last winter, and +39C last month. If a 100,000 sq. m. installation works here, then with the right planting, it must be possible anywhere.