Finding Green Space in a Glass Canyon

When Zeckendorf Towers, a Manhattan condo complex at bustling Union Square, decided to replace its leaking roof with an environmentally friendly green one, its board turned to New York Green Roofs for a design that would be complementary.

“The condo community is very proud of the fact they were an integral part of revitalizing Union Square in the 1980s,” Falder says. “Creating this green roof was just another way for them to be on the cutting edge of making the community better.”

New York Green Roofs teamed with the project engineer and the project roofer to conceive a standard green roof covering made from special underlayment, drainage, and sedum plants pregrown into vegetative mats provided by Xero Flor America, LLC, and these were installed much like sod. At the roof’s base is a Terranap Waterproofing system by Siplast. The roof sits seven stories above Union Square, now detailed with small hills and berms; a wide variety of vegetation including trees, shrubs, and flowering perennials; paving stones; and dramatic lighting.

“We wanted to keep the roof low-maintenance, and the more plants you add, the higher the maintenance,” Falder says. “We carefully chose plants that flower in succession so the roof is interesting in all four seasons.”

Far from being some exclusive sky-high area that residents rarely see, the rooftop garden is part of what’s known as the Sky Lobby for the condo complex, which comprises a cluster of four 24-story condo towers that flank the building’s lobby. “All of the residents of the building pass the garden day in and day out,” Falder says. “It really functions as a lobby of the apartment building.”

Zeckendorf Tower’s green roof also contributes to the area environmentally, Falder says. The green roof is located atop the busy Union Square subway station and helps reduce storm-water runoff into the subway station. “The number one reason for municipalities to encourage green roofs is to mitigate storm-water runoff,” Falder says. “A green roof turns an otherwise impervious rooftop into a living landscape that will actually retain water from precipitation.”

For cities with combined sewer systems, a green roof can reduce 40–60 percent of the water that would otherwise run off the roof and overflow the sewer system and force raw sewage into nearby lakes and rivers. “At Union Square, every time there is a big rain event, the subway is affected and revenue is lost,” Falder says. “That’s what makes the green roof such a great project for this area.”

Because of such benefits, the city of New York provides tax-abatement incentives for green-roof projects, and Zeckendorf Towers took advantage of the deal and offset the cost of its green roof by about $60,000 of the total $330,000 cost. Green roofs have not yet been mandated, but Falder says they are helpful for projects aiming to earn higher levels of LEED certification.

The Zeckendorf roof is likely to have a longer life thanks to its green properties. “Because we put a green roof on top of the new roof, that new roof is not going to be exposed to UV rays, which cause degradation of membrane,” Falder says. The green roof will also keep the roof significantly cooler during hot weather and will reduce the hot and cold fluctuations that can damage waterproofing membranes over time. However, Falder says the best benefit is the pleasure the roof gives the residents. “Sometimes I’ll be in the hallway at the project,” she says, “and someone will walk by and say, ‘Isn’t it so great?’” ABQ