Roofs Paved with Green

For Joe Hagerman the transition from streets to rooftops has been a natural one, conceptually speaking. Over the past year he has researched how his Biopaver design, which embeds pollutant-filtering plants into city paving stones, can be adapted to improve green roofs. The result is a streamlined system that he believes is easier to install and provides better insulation. It will soon be put to the test on a New York City school, where Hagerman hopes to demonstrate its benefits—not only for the future of green-roofing but also for the local community.

The principles behind green roofs are similar to those of Biopaver, a cowinner of the Next Generation award two years ago. Plants, and the soil they grow in, act like a sponge to capture excess rainwater, limiting runoff that would otherwise flow into overburdened, leak-prone sewer systems. Certain plants also have the capacity to filter out pollutants through a process called phytoremediation. “The larger concept behind these designs is to take something that’s impervious and make it pervious,” Hagerman says. “Then you make the pervious medium act like a filter so it can actually do some environmental work.”

In the fall of 2005 Hagerman earned a research fellowship at Rafael Viñoly Architects (RVA) based on a proposal to study how the fundamental properties of Biopaver (patent pending) could be applied to the building envelope. The fellowship came at an opportune time: green roofs were on everyone’s mind at the firm during the construction of the Janelia Farm Research Campus, in Virginia, for the Howard Hughes Medical Institute. One of the largest green roofs in the country, the 255,000-square-foot meadow that blankets the campus integrates the building into a sloping landscape, with additional green terraces stretching in layers across the front facade. “There was a lot of shop talk within the office about that roof,” says Ned Kaufman, Viñoly’s director of research and training, “and that began to inform Joe’s thinking about what other directions could be.” On his first day at the firm, Hagerman had the opportunity to walk this monolithic roof with the designers. “I got to see what their goals were and how the system worked—and what happens when a building becomes part of a landscape,” he says.

Janelia Farm also revealed some of the limitations of existing systems and products. Traditional green roofs stack multiple layers of materials between the greenery and the roof membrane to ensure that the structure is properly drained, insulated, watertight, and durable. In addition to being complicated, these extra sandwiched layers make it hard to assess the roof’s thermal efficiency if a failure occurs in the membrane. Furthermore, performing maintenance checks on monolithic systems means digging up the roof and depositing the debris in landfills. “Part of Joe’s thinking evolved as a kind of critique,” Kaufman says. “He thought, ‘How can we do things better, or differently?’ ” Hagerman’s solution cuts down on protective layers by integrating hydrophobic insulation materials. “Green roofs are great when the sun’s out, but ultimately the roof’s insulation layer dictates how well your building performs when it’s cold outside,” Hagerman says. “You have to rely on that insulation not being compromised by water damage.” He opted to use a sustainable glass-based material called Foamglas (made by Pittsburgh Corning), which is more water-resistant than the usual polymer-based material, as an insulating layer. Moreover, the modular system, composed of blocks of insulation and planting trays of lightweight Gaia Institute soil, makes installation easier. Still, landscape architect and green-roof expert Diana Balmori ­worries that the simplified system does not have a water-retention mat or cups. “They serve as a reservoir for time-released irrigation while also shedding storm overflow,” she says.

Hagerman and his partners will soon find out how their design performs. After months of research, they are now ready to apply the system to a real building. “We were going to do a demonstration on the roof of RVA’s own building,” Kaufman says. “But we realized that if we could make this project more ambitious, we could develop some really interesting ideas in partnership with a school.” Those ideas include a curriculum that would engage students in a hands-on discovery of science and math using a Hagerman green roof planted with native species as a learning laboratory on top of the school. The plan was particularly appealing to directors at the Salvadori Center, an architectural and engineering education group with whom Kaufman had worked previously, whose mission seemed perfectly suited to the project. “We use the built environment as a springboard for interdisciplinary learning,” executive director Dr. Leonisa Ardizzone says. “We’re especially interested in moving into the area of sustainable design—we already had a green-roof curriculum in our bag of tricks.”

The Salvadori Center connected Kaufman with the Stevenson campus in the Bronx, which houses six schools, including the Pablo Neruda Academy, a high school with an architectural focus. “It’s a real boost for this area,” says principal Dina Heisler, who is delighted that her students could get the chance to be part of the larger dialogue in environmentally minded design. “It’s a natural fit for our school to explore not only the built environment,” she says, “but also the way it intersects with the natural environment.”

The experimental roof won’t just be a learning tool for Stevenson students. “This roof is going to be a platform for ongoing research in the same way that it’s a platform for hands-on teaching,” Kaufman says. Using data gathered from the roof by students and specialists, researchers from the Federation of American Scientists will be able to study how green roofs function by measuring its effect on the microenvironment. Hagerman also hopes it will offer therapeutic space for a local health clinic and a focus for the neighborhood. “What we’re doing with the school is way more important than my system because it’s a new way of thinking about why you green a building,” Hagerman says.

Though approval for the project is still pending, all the partners are committed to making sure that they get their green-roofed school—at Stevenson or elsewhere, if necessary. “It would be lovely if it happened at Stevenson,” Ardizzone says. “But it would be such a gift to New York City that we would just like to see it happen and then use it as a model for what green roofs could be.”