By Steve Urbon
NEW BEDFORD — The Hanging Gardens of Babylon it’s not. But the new roof garden of the Buzzards Bay Coalition is making a very different statement 2,600 years after King Nebuchadnezzar tried to lift the spirits of his homesick Persian wife through rooftop cultivation.
This time around, it’s a green statement, explained coalition director Mark Rasmussen. It is going to help with everything: storm runoff, oxygen-generating green space downtown, climate control in the building, and, with the solar arrays, sustainable electricity generation.
The garden sits atop the organization’s new headquarters downtown, which is in the final stages of construction leading to its Aug. 27 grand opening. There will be a lot of energy-conscious features to point out in the rebuilt 1836 Coggeshall Counting House on Front Street.
But the roof is the first of its kind in the city, a high technology version of an ancient concept that is being adopted worldwide as a big boost in sustainability.
This being 2010, it involves much more than dropping a load of dirt on the roof and planting grass and plants. For one thing, the roof has to support the weight, so the building design had to take that into account. For another, the roof is intended to be low-maintenance and high efficiency, so it involves a great deal of engineering innovation and modern materials.
The contractor, Carlisle SynTec of Carlisle, Pa., starts with a waterproof membrane then adds 5 inches of foam insulation, a layer of honeycombed plastic water collection mats and 4 inches of specially formulated, relatively lightweight dirt.
“This roof is rated R-56,” Rasmussen boasted — a big plus in hot and cold weather alike.
Atop all of this is a layer of sod, called mats — but it’s not grass, which would require mowing. Instead, the design uses nine different varieties of sedum, one of which blossoms bright red. It’s a succulent ground cover that holds moisture, grows to only a few inches, and requires no maintenance, Rasmussen explained.
The result, he said, is a roof that can absorb and later evaporate half the water in a major rainstorm, keeping it from the already overloaded city sewer system. It was a hot day when he showed a reporter the roof, yet instead of shooting up to 140 degrees or more the way it would on a rubber roof, the roof garden was no hotter than the air at ground level.
And despite the fact that the roof has been in place for a few weeks, there were no bird droppings, no seagull nests to foul the planting.
That’s thanks to small speakers emitting an ultra-high-pitch tone that most adults can’t hear but which drives birds to distraction — and away from the roof.
All of this, sad to say, won’t be on public exhibit. The roof is invisible from the street, hidden behind a metal edge several inches high. The coalition’s intention was to build a green building with a fully restored exterior. So there is no guardrail to keep people from the edge, because that would change the look of the exterior.
But there are two possibilities. For the August grand opening, Rasmussen said, the coalition is looking at putting up a temporary fence of some kind to keep people safe on the roof.
Second, it’s more than a block away, but the patio of the San Francisco Room at the Whaling Museum is perhaps the one public space that has a view of the roof garden. Bring binoculars.
Steve Urbon is senior correspondent of The Standard-Times.
July 26, 2010 12:00 AM