Marci Cole Ekberg admitted that the roof on Save The Bay’s waterfront headquarters at Fields Point in Providence made her a little uneasy at first.
It didn’t seem right to have various plants and grasses growing directly out of the pitched roof. After all, roots and water are the enemy to most structures – roots can tear at a building and water can rot it away.
Seifert Systems Invests in Energy Efficiency to Strengthen Operations
For manufacturers, energy is more than just another operating expense. It plays a critical role…
Learn More
And every time it rained, the water-soaked soil on the roof weighed all that much more. “We were a little nervous for the first few days,” Cole Ekberg, a coastal ecologist at the nonprofit organization, joked last week.
But for two years, the so-called “green roof” at Save the Bay has performed perfectly, with the succulent plants and grasses reducing rainwater runoff and cutting down in a small way on the pollution flowing into Narragansett Bay.
It remains, however, one of only a few vegetative roofs in Rhode Island.
That may change, some predict, as more government agencies and companies embrace energy conservation and environmental protection and turn to using “green” building practices and materials in construction projects.
Glenn Szalay, New England regional manager for Canton, Mass.-based waterproofing manufacturer Sika Sarnafil, said about 5 percent of the company’s work is related to vegetative roofs. “But we expect that number to start growing a lot more rapidly,” Szalay said.
Green roofs have been around for thousands of years. In fact, one of the best-known early examples of a green roof was the Hanging Gardens of Babylon, built on terraced structures about 500 B.C. It was considered one of the Seven Wonders of the World.
In modern times, green roofs gained popularity in the Europe in the 1960s as the technology allowed for plants to be grown on rooftops without the possibility of damage. Still, the green roof has failed to reach widespread popularity in the United States.
Advocates note that vegetative roofs can cut heating and cooling costs, pointing to studies have shown that plant life flattens out spikes in roof temperature during the summer and helps a building retain heat in the winter.
They also say these roofs can reduce roof water runoff, thereby reducing a strain on nearby sewer systems. “It makes sense that it will absorb more water for nutrients and for growth,” Szalay explained during a presentation sponsored by the American Institute of Architects, Rhode Island Chapter, late last month.
But upfront costs loom as a big deterrent. Szalay said depending on the type of vegetative roof – “extensive” roofs have a soil depth between three and seven inches, while on “intensive” roofs the soil depth can be four feet or more – going green can cost as much as twice as much as a traditional roof.
“When it comes to these systems, it’s an investment,” Szalay said, adding that vegetative roofs will likely outlast conventional roofs.
Jonathan Knowles, a New York City-based architect and assistant professor at Rhode Island School of Design, said he has heard some designers have shied away from plantings on rooftops because of the cost issue. He’s not one of them.
“Yes, you can get the environmental aspects of a vegetative roof much cheaper using other methods,” said Knowles, whose firm is working on a residential green roof in Massachusetts. “But obviously it ignores the aesthetic value and the ‘extra room’ possibility.”
Knowles supervised RISD’s entry in the U.S. Department of Energy’s Solar Decathlon two years ago, a competition designed to raise awareness of alternative energy sources.
In the competition, RISD students constructed a small experimental house that utilized solar energy. The house, which didn’t win, featured a vegetative rooftop that gave potential inhabitants extra living space.
Because of the difficulty in fixing leaks in vegetative roofs, those who install the waterproofing go through extraordinary steps to ensure a tight seal before soil is added. Indeed, Szalay said the cost of fixing a leak can be as much as 10 to 20 times the cost to install the roof.
“It’s not a fun phone call when you’re talking about removing 12 inches to two feet of soil,” he told the gathering at the AIA-RI. “It’s a pretty costly proposition.”
At one project involving the Yale Library, a leak formed in the thermoplastic membrane three years after Szalay’s company had installed it for the library’s vegetative roof. An investigation revealed that before the soil was placed on the roof, a landscaper’s heavy machinery had penetrated the membrane. “It took three years to leak, but it leaked nonetheless,” Szalay said.
Still, such occurrences are rare, Szalay insisted. “The chance of a leak happening, after all the quality control, is pretty slim,” he said. “Nothing lasts forever, but these roofs could last a long, long time.”
But Szalay said an unexpected problem also developed at a green roof project at the Howard Hughes Medical Institute in Dulles, Va.
Because the building was cut into the side of a hill, deer were able to roam at night on the 230,000-square-foot roof, which is covered in meadow grass. Every morning, workers were finding that deer had fallen off the roof to their deaths. A railing was quickly installed.
“The deer were running across the field and the field suddenly stopped,” Szalay said. “[The institute was] wondering why their workers were coming to work early. They were fighting over the deer meat.”
When a green roof was installed in a $1.1 million project at Fort Adams in Newport two years ago, it was a matter of historic preservation.
Arnold Robinson, project manager for Newport Collaborative Architects, said that when the fort was built in the 1800s, it had an eight-foot-deep earthen roof topped off with sea grass. But despite a sublayer of lead flashing designed to divert water, the roof had always leaked.
Robinson said workers “peeled off” six feet of soil and installed Sika Sarnafil’s thermoplastic membrane, then returned the soil and replanted chewing fescue and field grasses. Szalay said it’s believed that Fort Adams is the first structure of its kind that has been successfully waterproofed.
Now Newport Collaborative is in the planning stages for another green roof project. Robinson said a South County charter school with an environment curriculum – he wouldn’t identify it because the project hasn’t received a green light – is interested in a vegetative roof.
In 2004, the South Providence Development Corporation had a rooftop of sedum planted at its business incubator at 17 Gordon Ave., Providence. It was part of a larger effort to use green building practices that included constructing a porous parking lot to absorb rainwater and installing a solar panel for electricity.
At Save The Bay headquarters, Cole Ekberg said the vegetative roof is part of an elaborate system of plantings and berms that prevents most of the rainwater from the roof and the parking lot from draining into the Bay. The vegetative roof can absorb a half-inch of rain before there’s any runoff, according to Cole Ekberg.
But there is a weak spot in the system: Some of the building isn’t covered by a green roof, and water runoff from those areas has gouged the earth where it flows toward the Bay.
“It’s a really good contrast between a green vegetative roof and a side that doesn’t have a green roof,” Cole Ekberg said. •
