When Mike O'Brien decided to build a home from scratch for the first and only time, he already knew he wanted a carbon-neutral house. Given the fierce demand for close-in housing in Portland (Ore.), O'Brien figured he could try out some innovations in his new home without worrying too much whether they would all work out. So along with the clay floors, solar water heater, radiant floor heating and Durasol walls, he installed an ecoroof. O'Brien, who is the Green building specialist for the city's Office of Sustainable Development, found his first challenge was locating a roofing contractor who would install home ecoroofs.

"There are commercial companies in Portland that say they'll do ecoroofs, but they aren't interested in doing houses, and they don't want to do it on a sloped roof,
he says.

O'Brien's problem began moving toward a solution when Katie Colgan, a student in community development at Portland State University, agreed to coordinate his roofing project. Colgan and her crew, GRIP (Greening Rooftops in Portland), also students, provided the labor gratis; O'Brien only paid for materials.

Constructing The Roof
A waterproof membrane is essential to ecoroof installations. O'Brien went with EPDM rubber, but before he rolled that out, he put down two layers of an asphalt membrane. He did that because he couldn't get a commercial roofer to put in a higher-quality commercial membrane for his smaller-size roof.

O'Brien has a roof with a 4:12 slope, which is about the maximum degree possible now, according to the Ecoroofs Everywhere website. There's a rafter ceiling underneath the roof; the rafters are 2x6 and 16 inches on center. Before installation on the roof began, O'Brien checked with the structural engineering firm that designed his home to make sure that it could carry the load of the ecoroof.

"I asked them to look at 25 pounds per square foot, which is actually double what it would ever really be if, for example, the soil was completely saturated with water,
he says.

Water Need
After the engineers Green-flagged the project, O'Brien went ahead. He's now planting drought-tolerant sedum and sempervivum in four inches of a growing medium that includes a lot of pumice, for good drainage. A jute geotextile will be laid over the plants and soil, and perforated metal will be placed around the edges to hold the soil in place and allow water to escape.

Ecoroofs Everywhere recommends watering ecoroofs over their first two summers, especially in dry summers. O'Brien says he'll be able to irrigate his ecoroof by stepping up onto the roof from his terrace, where he has installed a hose bib. If he chose not to water the roof, the plants would simply go dormant over the summer.

"Part of what I was trying to do with this house is think about the climate of the future, which looks like it's going to be warmer and drier, and put things in the house that would keep it cool without using air conditioning,
O'Brien says. "So the ecoroof is part of the cooling strategy.

Benefits
Ecoroofs not only provide savings in heating and cooling costs, they also provide an insulating layer that reduces sound, according to greenroofs.org. While installation costs may be higher-Ecoroofs Everywhere gives a general estimate of from $6 to $16 per square foot, accompanied by many caveats, and BN's research turned up averages much higher than that-ecoroofs have a life expectancy of up to 50 years, if installed properly.

Maintenance may be required during the two years it typically takes the ecoroof to mature, depending on the plants selected. However, if the plantings are densely done in a soil with low organic matter, little or no weeding should be required, according to Ecoroofs Everywhere. Fire hazard shouldn't be an issue, because the sedums predominantly used for ecoroofs are natural fire retardants.

The City of Portland Ecoroof Program lists several benefits that accrue from ecoroofs. One of those, particularly important to this city with its antiquated stormwater system, is lowering both the amount and the temperature of stormwater runoff. In a recent story that ran in Sunset magazine, Tom Liptan in Portland's Bureau of Environmental Services said that a half-million gallons of water could be kept out of the system for every acre of impervious surface replaced with an ecoroof.

Ecoroofs are considered an approved stormwater management technique under Portland's Stormwater Management Manual requirements for new development and redevelopment.

Ecoroofs haven't escaped attention from lawmakers, either. A Philadelphia city councilman has introduced legislation to offer tax credits to residents who put a lawn or garden on their roof. The councilman's proposal offers a 25 percent credit against the cost of installing a Green roof system, including the multilayer assembly, waterproof membranes, a supplemental roof barrier, if needed, and appropriate drainage.