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Green roofs spring up across the Northwest

by Pat Munts

Green roofs are gaining acceptance as their value in reducing rainwater runoff and lowering heating and cooling costs become more evident.

Portland, Ore., actively supports eco-roof construction by offering a $5-per-square-foot incentive to encourage the construction of 43 acres of roof gardens by 2013. The program could potentially cost the city about $6.5 million in incentives but save $15.8 million by avoiding stormwater costs. The majority of green roofs have been installed on commercial properties, but there's nothing to keep a homeowner from using these same techniques to green up their home.

Although the idea is appealing, there are some important things to consider. "Installing a green roof is not a do-it-yourself project," says Colin McCrate of Seattle Urban Farm Company in Seattle. "There's a lot of engineering involved in doing it right." Costs can vary depending on the amount of retrofitting required and types of plants used.

McCrate says that most buildings older than 5 years aren't easy to re-engineer for a green roof. "There may be too much reinforcing needed," he says. When his company built the herb and greens garden on the top of the Bastille Café in Ballard, Wash., he had to call in a structural engineer to design the reinforcing to hold up the roof, plants, beds, soil and a full load of water. "It's an expense a lot of homeowners may not want to make," he says.

Selecting the right roofing system also makes a difference. "Choose a roofing company that has the experience and training to install a living roof," says Damon Shelton of Elements Smart Roofing and Jones Boys Maintenance and Roof Care in Seattle. The Elements Smart Roofing system and those similar involve the individual engineering of a roof and then the installation of appropriate waterproof membranes, engineered soils, water flow and irrigation systems and plants.

The plant palette for a roof depends on how it will be used, says Sean Hogan of Portland-based Cistus Nursery and Design. Even then, there's no set list of plants that should be used on a project. "At this stage, we are learning to adapt roof plantings to Northwest native plants that can handle our dry, hot summers instead of the traditional European plant palette," he says. Hogan and other designers are experimenting with low growing, drought tolerant Northwest native plants that can handle the wet winters and brutally hot summers.

Hogan consulted on the roof garden redo on the M Financial Building in Portland, which incorporated shaped mounds planted with colorful plants. To mimic nature on the roof, the dips between the mounds have plants that can handle more water. "What you plant changes with each roof," he says.

Green roofs will need water during dry months to help the plants out-compete weed seeds that will blow in. Thin patches may need to be replanted to maintain a good cover. Ornamental and food plants in pots will need to be monitored closely for water, as roofs tend to be both windy and hot.

Pat Munts grew up in western Washington but has spent the last 30 years gardening on the dry east side of the state near Spokane. She freelances for the Spokesman-Review and has served as eastern Washington editor for Master Gardener Magazine. She's the small farms coordinator for both WSU Spokane County Extension and the Spokane County Conservation District.


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