Northeastern University’s campus was established in 1898 primarily as a day, or “commuter school.” By the late 1980’s, the campus grounds largely consisted of asphalt walks, parking lots, and hard surfaces in which the old buildings clashed aesthetically with a new evolving architecture. Students and faculty did not feel safe and the campus atmosphere detracted from a positive academic experience. In an effort to increase its residential student body, the University launched an urban renewal plan aimed at transforming its campus environment. Since 1990, the university has invested millions of dollars in landscape improvements—creating a green campus with more student oriented spaces.
Pressley Associates has been instrumental in helping Northeastern rejuvenate its campus. The company has assisted the University by defining recognizable entrances and gateways to the campus. Courtyards and tree-lined promenades have replaced concrete plazas, parking lots and paved service drives. Active and passive lawns and varied seating spaces have strengthened the sense of community and have provided a sustainable answer to the paved urban environment.
Development of the Behrakis Roof Garden
The Behrakis Health Sciences Center Roof Garden presented Northeastern with a unique opportunity to advance the concept of a campus landscape one step further. In 1999, Pressley designed the one-acre green roof above a new parking garage. Northeastern’s goal was to create a beautiful and usable area linking their new Health Sciences Center and a Residential Complex, which would house graduate students.
This $80 million expansion presented the University with an opportunity to create green space on its West Campus and an urban garden for the Northeastern community, on what would otherwise have been an unattractive and unusable roof top. The roof garden was an important element in unifying the new complexes and weaving the facilities seamlessly into the campus.
The one-acre garden was designed to facilitate access to and from the upper levels of the Health Sciences Center and Residence Hall E. The rooftop design features two curvilinear paths that link three roof levels. The paths act as a spine joining an oval garden, the green lawn, and the rooftop plantings. The garden is also accessible from the ground level and provides an intimate green space for students who can lounge on the lawns, study, or take a break outdoors in between classes.
Inviting walkway on roof with integrated seat wall.
Image courtesy of Pressley Associates.
The Design Process
The Behrakis Health Science Center was a design/build project that required the sharing of enormous amounts of information in a timely manner. Pressley joined the design team early in the schematic design phase and worked closely with the architects and engineers who were designing the load support for the rooftop landscape.
During the design process, Pressley provided detailed cost estimates and studied the planting layout and circulation three-dimensionally. Computer models and a ¼ scale model helped Pressley convey to the client the design intent and limitations and opportunities of the unique rooftop environment.
Pressley also studied and calculated minimum soil depths for rooftop plantings. By specifying species of plants suitable for growth in minimal soil and windy conditions, and coordinating the placement of large trees with the engineering team, Pressley was able to reduce structural costs and utilize the space more efficiently.
The most technically challenging components of this design were the substantial slopes created by the architecture of the buildings and garage below. The construction of the rooftop garden over the parking facility necessitated careful contouring and ramping to respond to the sloped parking decks. This was complicated by the fact that design criteria, established early on in the design process, stipulated that handrails and railings should be minimized to reduce the sense of grade change and mimic a ground level landscape. Potentially steep slopes that were required to connect the three decks were articulated to adhere to ADA standards, while they remained purposeful and graceful.
Although the building was designed with the intention of a roof garden, load tolerances were an issue throughout the process. An innovative approach to achieve sloped lawn areas with minimal soil weight was to place large Styrofoam blocks wrapped with waterproof membranes in unplanted spaces below the soil. This was a cost effective alternative to using a lightweight soil mix, which was installed in the remaining areas of the garden.
Curvilinear walks and mature planting on Behrakis roof.
Image courtesy of Pressley Associates
Benefits of the Roof Garden
This Behrakis Health Sciences Center Roof Garden benefits dormitory residents, students, faculty and the Northeastern community in ways that nearly overshadow its ecological function. The ability to insulate the garage roof, process groundwater runoff, as well as protect the roof membrane from ultraviolet rays adds substantially to the project’s economic value.
As an insulating layer, the roof garden regulates the temperatures in the garage below. In the summer months, the garage maintains a temperature thirteen degrees cooler than ground level and during the winter, temperatures are several degrees warmer. There are also positive returns to the adjacent classrooms’ and dormitories’ overall operating costs. The garden’s design, which incorporates lawn, shade trees, ornamental grasses and shrubs adjacent to the glass wall of the Behrakis Health Science Center, reduces glare and heat gain, thus boosting the building’s energy efficiency usage.
Behrakis rooftop at night.
Image courtesy of Tim Hursley.
Large areas of lawn, lush shrub plantings and large caliper trees were installed to beautify the garden, but also reduce runoff to the public sewer system. While unable to absorb all of the rainwater that falls on the roof, the plantings greatly reduce water being directed to roof drains, and assist in filtering unwanted contaminants and particles before the water reaches the public system.
As an extension of the numerous landscape improvements completed in the surrounding campus, the benefits of the Behrakis Health Science Center roof garden can be measured in small yet meaningful ways. Occupying an area that had previously been a paved parking lot, and could have been a gravel covered roof, students, faculty and staff benefit from green space in an unexpected urban form. Wildlife is attracted to the perennial garden and students lounge on seatwalls and relax on the lawns.
At approximately $20 per square foot, the Behrakis Health Science Center rooftop garden was slightly more expensive than a typical on-grade landscape construction project. Large amounts of softscape and minimal paved areas helped to offset the higher cost of lightweight soil, waterproofing techniques, and construction access limitations. It was completed in the spring of 2003 for $800,000. The combined rooftop and ground plane landscape area totals approximately 82,800 sq. ft. Constructed prior to the ‘green’ initiative currently being embraced by many construction managers, the Behrakis rooftop has been a great success for the University community and design team members.
Sara Forbes is the Marketing Director for Pressley Associates, Inc. in Cambridge, Massachusetts and can be reached at: firstname.lastname@example.org