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Planting trees is still the simplest way to cool your home and help capture carbon dioxide in the atmosphere. But buildings such as Chicago's City Hall and the new California Academy of Science in San Francisco now have their own leafy canopies--green roofs created from a mix of plants selected for rooftop conditions. So, is a green roof in your future?
"It will cool the ambient temperature in summer, provide wildlife habitat, and absorb storm water to reduce runoff," says Sarah Murphy of D.C. Greenworks, a nonprofit that installs green roofs on homes. She helps homeowners decide about a green roof by sharing these facts:
Structural load capacity. A green roof is made up of a waterproofing membrane, a root barrier, a drainage layer, soil or other growing media, and plants. This can weigh 20 to 25 pounds per square foot, Murphy says. An architect or engineer must certify that the roof can handle the load.
Maintenance. Green roofs require attention during the first year. Most installers include the first year's maintenance in the price. After that, you need only make an annual trip up to pull weeds and give a light feeding.
Plant selection. "It's very important to pick the right plants for your climate," says Ed Snodgrass, author of Green Roof Plants: A Resource and Planting Guide. The ideal plant for a green roof needs little water and also produces a shallow root system that can survive in as little as a few inches of soil.
A green roof is not a do-it-yourself project. "This isn't gardening," Snodgrass says. "It demands engineering, roofing, hydrology, and plant knowledge."
Still, he thinks the effort is worth it. "It's a joy to watch your roof grow and bloom."
