By now, most of us are familiar with the concept of a green roof: Take some sun- and drought-tolerant plants, place them in watertight containers and line up the containers on the roof. With little or no care after this initial work, you’ve reduced the amount of sunlight hitting the building below, and you’ve cut back on the amount of rainwater pouring into the gutters and, later, into streams, rivers and bays. It saves energy, it reduces the load on storm systems and it has a positive impact on reducing greenhouse gases. With just a few tips, just about anybody can do it.
This idea, which is rapidly gaining currency in cities and towns across the country—the square footage of green roofs in the United States climbed by 28.5 percent in 2010, according to Mother Earth News—is, as a matter of fact, simple. But to make it work for a structure the size and impact of the new John and Frances Angelos Law Center, currently under construction on the University of Baltimore campus, significantly more effort is required.
When the building opens in 2013, there will be not only ground cover and other plantings set up on its various terraces and other flat spaces but also trees and shrubs that will provide color, shade and a pleasant backdrop to what is otherwise a wholly urban space. The goal is to provide the respite of a natural environment that the UB School of Law community can experience all year long, from a breezy spring day through the heat of summer and into the depths of a Maryland winter.
The Build Up got some insight into plans for the green roof terraces from Joe Wahler, associate landscape architect at Stephen Stimson Associates, the landscape architect firm hired to plan the various green installations for the building’s exterior. Wahler emphasized that with proper planning and expertise, the plantings around the law center can reap a number of benefits. But it takes more than a plastic tray and a green thumb to do it right.
“Planting on green roofs requires careful attention to soil design, drainage and species selection since these plants are exposed to extreme variations in temperature, solar reflectivity from the building and limited soil volumes,” Wahler said. “The majority of the selected plants are natives of the region that can tolerate these conditions and provide year-round interest and habitat.”
How “extreme”? Try well below zero (considering the wind chill several yards above the ground) to highs in the 110s and even the 120s. It takes something tougher than your average potted fern to make it in this kind of environment. And remember, these plants are not meant to be brought in out of the heat and the cold—they will be a permanent outdoor fixture.
To prepare for the installation, workers made sure the structures holding the plantings are watertight, with drains designed to capture precipitation and irrigation that will be applied to the greenery. Soil depths and composition are determined by the structural capacity of the roof and by the growth requirements of the plants.
Wahler noted that while some spaces have less than six inches of soil, others will be significantly deeper.
“Raised planters made of stainless steel and precast architectural concrete create deeper soil profiles that can support herbaceous perennials, shrubs and trees,” he said.
The trees, several of which are already planted on the south and north sides of the building, are at a height visible from the street. While they won’t grow to enormous size, they will be a large, leafy feature of the center’s design—and no doubt a favorite spot for gatherings on the terraces.
Decking and seating have been added to enhance the look of these spaces, and on the south side, a canopy is being readied for installation. Small rocks, spread out as a buffer, add color and texture to give the spaces the inviting feel of a patio. In all, it’s another great place for students, faculty and alumni to spend some time a bit removed from the hustle and bustle of the city below.
Wahler explained that the principal intent of the law center’s green roof is focused more on water and less on the sun.
“The benefits of green roofs are the slowing and filtering of storm water runoff by the soils and plants,” he said. “The proposed plantings will provide shading of the terrace[s], but will not provide significant shading of the building.”
In fact, managing the amount of solar gain in the law center is the job of its innovative systems for handling air and light. Still, the close proximity of trees and plants, both inside and outside the center, undoubtedly will have a positive effect on its inhabitants regardless of the season.