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Solution of the Month


Roof Positive: Meg Needle, AIA, LEED AP, and GRP, welcomes the newfound popularity of green roofs—and the challenges that come with it.

Lord, Aeck & Sargent
December 2009

By David Sokol

Architecture recently welcomed a new professional acronym into the fold. It is GRP, which stands for Green Roof Professional. The 5-year-old not-for-profit association Green Roofs for Healthy Cities bestows this accreditation, and earlier this year the first 127 individuals successfully passed the 100-question test that earns the initials.

Southface Eco Office by Lord, Aeck & Sargent
Photo © Jonathan Hillyer

Southface Eco Office by Lord, Aeck & Sargent
Atlanta, Georgia

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Meg Needle is an associate at architecture firm Lord, Aeck & Sargent, and a member of that inaugural group. She admits that green roofs are “more of a niche market” than sustainable design as a whole, but that the GRP designation suggests a growing interest in that niche. For further evidence, she points to the incorporation of green roofs in municipal codes, as well as the burgeoning popularity of extensive roof systems. “However,” she cautions, “If the roof vegetation doesn't thrive, or it leaks, all bets are off.”

For waterproofing, Needle prefers hot rubberized asphalt, which achieves a seamless finish and resists root penetration. Just such a system was used for the Lord, Aeck & Sargent-designed Gwinnett Environmental Center, although its 40,000-square-foot sloped roof presented the bigger challenge of “making sure the landscape takes hold.” To stabilize those pitches and prevent erosion, Needle’s team used a cellular confinement system—“ribbons of perforated reinforced plastic banding joined like an accordion that open up like a paper wedding bell. It was developed to build landing strips during the first Gulf War, but the problem with a roof application is that you can’t stake it.”

“We ended up using custom ridge supports that we were able to bolt at the top,” Needle says. “We set the angles on wood blocking, and the cellular confinement system just drapes down along the slopes.” Cricketing drains water from the roof’s valleys, and rain chains pierce through large horizontal overhangs.

For the more recently completed Southface Energy Institute, Lord, Aeck & Sargent developed a system to mount a deck atop an inverted roof membrane assembly. The extensive green roof provides ballast to the inverted insulation, but the observation deck required nailing into typical framing. “It makes it a little more challenging when you have nothing to nail into and you don’t want to nail the roof,” Needle says. “We ended up putting sleepers on top of the insulation, and the deck and railing were nailed to the sleepers; we allowed the drainage mat to run underneath the decking so roof drainage could still be facilitated.” In cases like this Needle advises taking care of sleepers’ direction so they don’t prevent drainage, and ensuring that the drainage mat completely covers the UV-sensitive insulation.

The increasing popularity of extensive green roofs promises wider deployment under more complex conditions. A new generation of GRPs is accommodating these evolving requirements without committing the cardinal sins of leakage or plant failure.

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