Anderson Design Center Addition to Vol Walker Hall Features Green Roof

Photo Submitted

The fourth level of the Steven L. Anderson Design Center addition to Vol Walker Hall features a green roof and a terrace made from recycled bamboo composite decking.

FAYETTEVILLE, Ark. – The Steven L. Anderson Design Center addition to Vol Walker Hall has a green roof, one of just a handful on the University of Arkansas campus. It's located on the fourth level, outside faculty offices for the Fay Jones School of Architecture.

Mark Boyer, interim associate dean and head of the landscape architecture department, has been researching green roofs for about a decade. He said they can be established in various ways, and they can provide tremendous benefits to the environment, to the structure and even to the people inhabiting it.

A green roof is simply a living roof. Part or all of a building is covered with vegetation planted in a growing medium, on top of a waterproofing membrane. A growing medium can be about half the weight of standard soil, and it comes in the form of volcanic pumice or expanded clay, shale or slate – which is heated to the point that it opens and creates holes and fissures, allowing it to absorb water. This medium is supplemented with organic material such as compost to nourish the plants.

Boyer has worked with U of A graduate students and professors in the horticulture and biological engineering departments to experiment with the amount of organic material used – from none to 20 percent – to study the resulting water quality. Rainwater leaches the organic content and runs off the building, and can impair water quality.

"We're trying to find a good balance between allowing the plants to thrive and survive but then not having a big impact on the water quality," he said.

The benefits of having a green roof include cooler temperatures, protecting the underlying roof, and reducing stormwater runoff. A green roof can help insulate a building, keeping it cooler in summer and warmer in winter and reducing utility costs. It can also improve the urban heat island effect. Roof temperatures can drop to 90 degrees from 160 to 190 degrees in cities, improving ambient air temperature.

A layer of living plants on a roof also protects the roofing material. The plants block the ultraviolet radiation that breaks down a typical roof. A typical roof also heats up during the day and cools down at night, a constant fluctuation of temperature called diurnal shock. Those temperature swings make the material expand and contract. Added to the ultraviolet exposure, the roof material breaks down and cracks, needing to be replaced.

"You put a green roof on, you get neither of those things," Boyer said. "You remove the UV radiation and you remove the diurnal shock."

Green roofs also can help mitigate the impact of the built environment by lessening the harmful qualities of stormwater runoff. They reduce the amount of stormwater that hits the ground, and they slow how quickly stormwater reaches an urban creek.

When it rains, the water that falls on impervious surfaces, such as roofs, streets and parking lots, has nothing to slow it down. It travels very quickly, the runoff creating flash flooding and quick-rising streams. When the water in streams rises quickly, that's when the most erosion occurs in those streams.

"So, we're causing a lot more erosion in streams," Boyer said. "They widen; they deepen; they put a lot more sediment into the system that affects habitat. Anything we can do to slow the water down before it gets into the stream is a benefit."

A green roof can also work in association with other low-impact development strategies, such as bioretention through rain gardens and pervious surfaces. A gravel sidewalk on the north side of the building allows rainwater to soak in where it falls rather than running off.

Rain gardens, like those located in planters on the west side of the addition, allow the rainwater to collect for a period of time so the plants can take up the water and transpire into the atmosphere. This provides cleaning benefits because of the biological and physical activity that occurs with the mulch, soil and plants.

A green roof is also another element to design. The green roof on the addition presents a border of low-growing plants, such as varieties of sedum, with taller grasses in the center.

The green roof on the fourth level is a fully inhabitable terrace that provides broad views of campus and the hillside beyond. The modular planting system takes up about 1,300 square feet of the total 2,800 square feet of the outdoor space. The remaining walking surfaces, including the south outdoor covered classroom, are comprised of a recycled bamboo composite decking with glass railing at the perimeter.

Boyer said there's an aesthetic value to a green roof beyond the fact that it looks good. There can be a monetary benefit when it comes time to sell a building, especially in areas of high-density housing. A condominium that looks down on a green roof can be sold or rented for a higher price.

It also has been documented that plants help patients in hospitals heal faster, so those health benefits would carry over to the general well-being of people living and working near plants.

The first go-to plant for green roofs is sedum, of which there are several varieties on the green roof of the design center addition. These plants have a physiological process through which they can actually close their stomata – their openings in their leaves – during the day when it's hot, so they don't transpire during the day (when they'd lose the most water). They open their stomata in the evening and nighttime and do their transpiration then. This is done through the process of crassulacean acid metabolism, or CAM photosynthesis.

"Those plants are really well adapted to harsh environments – low water, low rooting conditions, intense sunlight," Boyer said.

Plants that will work well in deeper root spaces can even include shrubs and trees. Irrigation opens up more possibilities, such as is happening on the addition's green roof. Plants used on this green roof include various types of ajuga, Italian arum, hostas, sedum, garlic chives, as well as grasses such as little bluestem, Texas bluegrass, mondo grass and sideoats grama.

Boyer developed his first green roofs in 2006 on the roofs of buildings at The Gardens, the tailgating area on the south side of the U of A campus. But those aren't easy to get to, and Boyer hasn't been able to take students to them because of liability.

The green roof of the addition, and the low-impact design elements on ground level, will be used in instructional ways for Fay Jones School students.

"We're always looking for places to take students to see things," he said. "Now we've got an opportunity where we can take students right to a safe facility, and they can observe what's going on with them."

An even more important impact on students' design education, Boyer said, is that these low-impact features used in the design of the architecture school building "becomes what they're used to," he said. "It becomes the norm, rather than this unique thing."

"We're still in the place here in northwest Arkansas where they're fairly unique things," he said. "And we need to get to the point where they're not unique anymore."

The green roof was made possible by J.E. Allen Co., based in Hot Springs. Owner John E. Allen made a gift-in-kind of plants and planting trays for the Fay Jones School's green roof. Allen also provided consulting services, equipment and labor for the installation, which took place in June.