Roof gardens: looking good, saving money
Once roof gardens were just a matter of aesthetics; now there's something called a "green roof" that has environmental benefits.
For example, the Ritz-Carlton Hotel & Towers off Boston Common has a green roof that's part garden, part sponge, and part insulation. Mayor Thomas M. Menino is urging developers to consider similar roofs for their new projects.
With seven inches of soil and seasonal plantings, the Ritz's green roof partly "functions as a retention pond," said principal Anthony Pangaro of Millennium Partners-Boston, the Ritz's developer. With a conventional roof, rain rolls off and quickly finds its way to street level and a storm-water drainage system, sometimes overwhelming it during heavy storms. A green roof, in contrast, sponges up rain. Some trapped water evaporates. What eventually gets to the storm system arrives in trickles not torrents.
"The water discharges over time so there isn't a flash surge you get from a bald roof," Pangaro said. (Like many large complexes, the Ritz has several roofs at various heights. Only one roof is green.)
Green roofs have other advantages. A conventional roof, which is usually a black rubber membrane, becomes a "heat island" on a hot day, noted John Dalzell, senior architect for the Boston Redevelopment Authority, the city's planning agency. Roofs are often the location of a large building's air-conditioning and ventilation systems. With conventional roofs, these systems operate in an "ultrahot environment," he said; on a green roof, heat doesn't build up as much so these systems work more efficiently.
"This isn't a pie-in-the-sky, tree-hugging sort of thing," Dalzell said of green roofs.
A green roof can help qualify a building for Leadership in Energy and Environmental Design, or LEED, certification from the US Green Building Council, but a green roof is not essential for a LEED rating, said council spokeswoman Taryn Holowka.
One project envisioning a green roof is the condo conversion of a former South End police station, which has attracted attention because of the involvement of design impresario Philippe Starck. Kamran Zahedi of Urbanica, one of the developers, said he'd been impressed by green roofs he'd seen in Germany. When the city urged developers to try something "green friendly," they opted for a green roof, he said.
For the Clarendon, a residential tower proposed for the Back Bay, early blueprints call for several green roofs at various heights, said Robert Puddicombe of the Related Cos., a project developer. Green roofs, he said, "create a great insulating barrier."
At Landworks Studio Inc. in Salem, the firm that designed the Ritz's green roof, principal Michael Blier is excited about a South Boston project. Many green roofs have soil about eight to 12 inches deep and use plants needing little water, he said. But the Southie project, near the Broadway MBTA stop, could have green roofs with soil five feet deep to support lightweight, shallow-rooted trees. The project is called the Macallen Building Condominiums, and the developers, Pappas Properties Inc., contemplate a design that would qualify it for a gold LEED rating from the Green Building Council, senior vice president Tim Pappas said. No residential building in Boston currently has a gold LEED rating, Holowka said.
The cost of a green roof is hard to calculate, partly because it's also an amenity that can help sell a place to environmentally conscious consumers, developers said.
At the Ritz, Pangaro said: "Many of the people who stay in the hotel request a room that overlooks the green roof. It's so tranquil."
Chris Reidy can be reached at reidy@globe.com.
