Greening Your Roof

If you want to install a green roof on your home, odds are you'll be the first on your block to do so. Unless, that is, you live in the ecologically savvy Northwest U.S., where around 50 residential roofs already exist, according to Patrick Carey, a Seattle architect and director of the green-roofs project of the Northwest Eco-Building Guild.

Pioneers reap many benefits: Not only does green-roof technology on your home make your roof last longer, it reduces air-conditioning bills, cuts down on water runoff and improves your view. "You can look out the window and instead of seeing a hot and dry roof, you see something green," says Tom Liptan, an environmental specialist for the city of Portland, Ore. "You're improving livability."

So far, green roofs cost more than the standard sort. Suppliers are oriented toward commercial clients and haven't yet scaled down their products or their prices for homeowners. And you can count on hiring an architect or structural engineer to make sure your roof will bear the weight of plants and the soil medium.

Because of the expense, and because green roofs are simplest on flat surfaces, Liptan recommends that first-timers start off by having work done on their garages or on outdoor structures like garden sheds. If you plan on redoing the roof on your home, he suggests waiting until your current one needs replacing or at least serious repair.

Meanwhile, you can help reduce storm-water runoff by putting "storm-water planters" under the downspouts of your house's gutters. "Built above the surface, and filled with sandy soil and plants that can tolerate temporary flooding, they slow down rainwater, filtering it and allowing some of it to return to the atmosphere by transpiration," says Liptan. "The more storm water you remove from your sewage system, the less pollution enters your rivers and lakes."

You can also improve your environment by putting plants in containers on your roof or terrace. "To notice a difference in terms of reducing air pollution and lowering summer heat, cover at least one-fifth of the surface with plants," says Liptan.

Another low-tech way to boost air quality and reduce energy bills involves planting vines on your home's walls. "You are especially likely to conserve energy if you plant on the south side," Liptan says.

If you want tall vines that need support, such as clematis, large lightweight trellises are now available. "It's time for people to get used to the idea of mixing plants and buildings," asserts Noël Kingsbury, co-author of Planting Green Roofs and Living Walls.