Green roofs start to sprout on urban homes

Low-maintenance sedum cuts energy costs as well as greenhouse gases. Roofs are costly, though.

Every time it rained, Majora Carter cringed. "I lived in mortal terror whenever I thought it was going to rain," Dr. Carter says, remembering how the rainwater seeped from the street into her Bronx brownstone.

Then she and her husband, James Burling Chase, realized that the source of the problem wasn't on the ground, but on the roof. The stormwater system in their neighborhood backed up so quickly that the water rushed straight from their roof to the street – and into their home.

They decided to try a new strategy to fix an old problem: a green roof.

Now, after a substantial renovation, their flat roof has come alive – literally. Flowers and baby sedum are anchored in a thin bed of soil and gravel covering the roof. Golf-ball-sized stones frame this rooftop oasis.

Now their roof will retain about half the rainwater that falls on it, once the sedum matures in about two years. But besides finding a practical solution to a recurrent problem, Carter and Chase wanted a tangible way to show they were "walking the walk" when it came to their environmentalism.

Their home is the first in New York to feature such a roof. Green roofs have taken root on numerous commercial buildings across the country, but now people are exploring the possibility of planting a little shrubbery atop their own homes.

Karen Weber, founder of the green-roof promoting organization, Earth Our Only Home, says there are numerous benefits to green roofs:

•Energy savings of 10 to 60 percent, as the greenery acts as another layer of insulation from heat loss in winter and cooling loss in summer.

•Less noise (extra layers of plants and drainage materials act as insulators) and less greenhouse gas (like any green plants, those on a roof absorb carbon dioxide and give off oxygen).

•Doesn't trap heat from the sun the way conventional roofs do. Conventional roofs can overheat entire cities.

•Attracts pollinators like honeybees and bumblebees, which are often scarce in urban areas.

•Doubles or triples the life of the underlying roof.

But all the benefits must be balanced with the hefty cost. And turning a roof "green" demands more than flipping through the phone book for a contractor.

Although some may be tempted to do it themselves, Ms. Weber advises homeowners to resist the urge. First, call a structural engineer to analyze how much weight the house can hold. And while planting sedum on your roof may sound easy, it requires expert installation of layers of protection, drainage, and growing medium, says Dustin Brackney, a landscape architect with Cypress Landscapes in Cambridge, Mass.

Until recently, several factors have limited the number of green roofs on homes, says Melissa Muroff of Roofscapes in Philadelphia. Contractors like Roofscapes (one of the oldest and largest green-roof designers and installers) are not used to doing small roofing projects, while conventional residential roofers often lack green-roof expertise. That's changing, though, as more people are demanding green renovations, Ms. Muroff says.

The cost is high: between $15 and $35 per square foot. Carter and Chase's 1,100 square-foot brownstone roof cost $14,000 to design and install, more than three times the $6,000 it costs to replace a conventional roof of that size. It helps that the green roof will last an estimated 30 or 40 years, rather than the decade or so one might expect from a regular roof, Weber says. [Editor's note: The original version misquoted the price of the roof repair.]

The cost can be less if neighbors get together and use the same company to design and install several roofs at the same time. Muroff says the most cost-effective aggregate square footage for pursuing a green roof is 5,000 square feet or more.

Boston's hip Jamaica Plain neighborhood is contemplating moving in this direction as well. Forty or so residents gathered last month to hear how green roofs could work for their homes and community.

"Last year, if there was a meeting like this, two, maybe three people would have shown up," says guest speaker Weber. "Now this is a hot topic, and it's about cooling our cities and our neighborhoods down."

She says such roofs can work for almost any home, from the suburban pitched roof to the flat roofs on Jamaica Plain's "triple deckers" (three-family homes).

Although homeowners may want to make elaborate plans for an urban forest atop their home, most houses cannot support the intensive green roofs found on big commercial buildings, with trees and lush foliage. Residential installations mostly feature a maximum of four inches of soil.

The green sedum on the Bronx brownstone is the most common plant for residential green roofs, experts say. It is a succulent, flowering plant that requires little water and minimal soil (meaning less weight).

Although green-roof maintenance is necessary at first (the sedum requires occasional weeding or watering), once the roof is well established after about two years it only needs to be checked every six months or so, says Rob Crauderueff, the sustainable alternatives coordinator for Sustainable South Bronx (SSB), the nonprofit group Carter established in 2001 to help green the Bronx while developing a local, "green collar" workforce.

In the case of his home, Chase says he looks at the high cost as both a "romantic" and practical investment.

The romantic motivation comes from the feel-good moments he has watching sunsets – and the next Fourth of July fireworks – from their rooftop, all the while knowing they're giving a little bit of metropolis back to Mother Nature.

"Out here in the Bronx," Chase says, "we're starved for land to play with. There's no room for gardens in front of our homes.... Compared to some home improvements, this is a guiltless pleasure."

Carter and Chase also feel like they're giving back to the community by supporting the fledgling green-roof industry and having SSB employees perform the installation and maintenance.

Mr. Crauderueff recommends hiring a contractor who can design, install, and maintain a green roof so they have an added incentive to do a good job from the beginning.

Neighbors and a video crew from a new show on the Sundance Channel hosted by Carter gathered Oct. 5 to watch the installation of the green roof, which only took a day. The SSB crew used a "laddervator" (a ladder with escalator-like sides) to help carry the materials up to the roof.

The reactions to the new roof by her neighbors were varied.

"Some of them were probably like, 'Those crazy environmentalists are at it again,' " Carter says. "But I think there's a lot of buzz around here about green roofs, especially for storm-water management. They're asking 'Could that work for me, too?' "

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