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BY QUITTERIE GOUNOT

In print | Published September 23, 2010

As awareness of environmental issues has increased, student groups such as Good Food, Earthlust and the Green Advisors have formed and grown in order to tackle these issues. But in addition to student efforts, the college has also been attempting to increase its commitment to green technology through the installation of green roofs on campus.

There are currently three main green roofs at Swarthmore: the storage building adjacent to Papazian has one, as do residence halls Alice Paul and David Kemp. A first roof was installed on Papazion in 2002; a smaller roof, covering only 630 square feet, it allowed the college a low-scale trial before undertaking any larger projects. Shortly thereafter, plans were made for a 5,100 square foot green roof, above the third floor of Alice Paul, which was installed in 2004. In 2008, David Kemp was equipped with a five-level, 8,600 square foot green roof.

According to Scott Arboretum literature on green design, green roofs are “vegetated roof tops, comprised of a waterproof synthetic membrane topped with growing media and plants.” The kind of green roof at Swarthmore is known as “extensive.” As opposed to “intensive” green roofs, which support much thicker layers of foliage and even trees, “extensive” roofs accommodate a thinner, more modest set of plants and no trees. Intensive roofs are also sometimes used to grow fruit and vegetables.

A variety of vegetation can be planted on these roofs. The Arboretum staff recommends “low growing, shallow rooted, perennial” plants. They emphasize the need for these plants to be resilient, withstanding such natural adversities as temperature variations, wind, drought, disease and insects. It is also important to consider the proximity of a water source and the water retention capacities of the selected plants.

The main plant on the Papazian green roof is the Sedum sarmentosum, which has taken over virtually all other plants. “It’s a good and a bad thing,” said Gus Eriksen, garden supervisor of the Scott Arboretum. As a sedum, he explained, this plant is highly succulent, which is a major aim of a green roof, but the invasive plant could affect other plants from growing successfully.

In contrast, the vegetation on the green roofs on Alice Paul and David Kemp is more varied, spanning a wide assortment of species and colors. David Kemp boasts red sedum rupestre and Deslosperma nubigerum, which is a bright yellow flower. The careful selection process at play here looks for plants that are both biologically diverse and aesthetically pleasing.

From an environmental standpoint, these roofs are beneficial insofar as they mitigate the effects of storm-water runoff. Eriksen explained that before we lived in such densely constructed urban areas, rain water had a lot more opportunities to seep back into the ground. But the current landscape results in more erosion and runoff.

Green roofs also present significant financial advantages. While the initial investment is higher than for other roofs, green roofs enjoy a much longer life. By reducing temperature variations and protecting the actual roof from the negative effects of ultraviolet light, the vegetation on green roofs extends their life by two to three times. These roofs also have a significant cooling and insulating effect. As such, the Arboretum estimates that they allow for as much as a 25% reduction in cooling energy requirements for the top floor of multi-storey buildings like David Kemp.

Swarthmore’s green roofs are also visually appealing, and the roofs boast a habitat for all kinds of songbirds and insects, like grasshoppers, bees and dragonflies. Yet safety measures forbid access to the roofs outside of guided tours.

Claire Sawyers, the director of the Scott Arboretum, shared her dream of having green roofs that can be open to the community in the future. “It’d be great to have a green roof that is a living space for students to study and hang out in,” Sawyers said.

However, the roofs remain fairly unknown to many members of the college community. Even though there are tours and the College has received extensive praise for the roofs, many students have yet to learn about the roofs. Several residents of Alice Paul and David Kemp who were asked about the roofs reported knowing “very little” about them.

Engineering professor Carr Everbach was the one who first asked to have green roofs installed on campus residence halls. In a 2003 Environmental Studies Capstone Seminar, Everbach and others made clear Swarthmore’s opportunity and responsibility to lead in this area. There has been discussion of giving several other Swarthmore buildings new green roofs.

These plans are mostly uncertain for the time being, but the next green roof on campus will be on the Wister Center, near the Arboretum.

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