Rooting Another Chicago Roof

The green roof at the STEM Academy is constructed of eight layers starting with a rubberized asphalt membrane base and ending with pre-grown vegetation. Photos: Hanover Architectural Products

The Sarah E. Goode STEM Academy, in Chicago’s Ashburn neighborhood on the city’s South Side, offers a six-year program focusing on science, technology, engineering, and mathematics (STEM) to foster college and career readiness. Furthering students’ education and building efficiency are the school’s green features, including a 34,000-square-foot vegetated roof with a plaza and walkways. STR Partners, the lead architect in the joint venture, designed the three-story, 207,600-square-foot facility, and when its plans called for a green or vegetated roof, American Hydrotech was the natural choice.

The Chicago-based waterproofing and roofing product supplier has a long history of supplying projects throughout the city with green roofs. Over the years, American Hydrotech has completed dozens of projects for the Public Building Commission of Chicago, which controls Chicago Public Schools, the Chicago Public Libraries, Police and Fire Departments, and other city buildings. Many projects were watertight roofs and plazas, completed before vegetated roofs even came to the United States, but when Chicago mayor Richard Daley determined to make the city’s roofs greener in the 1990s, it was a natural progression for American Hydrotech to expand its product offerings. “We were already providing the roofing and waterproofing membrane, and adding the vegetated roof components was the logical next step,” says Ron Rediger, a manufacturer’s representative at American Hydrotech.

“When this project was announced, we made contact with STR Partners and explained our assembly,” Rediger says. “When it went out for bid, our authorized roofer, Anderson & Shaw Roofing, won the bid with the general contractor, F.H. Paschen S.N. Nielsen & Associates. The three of us together secured the whole project—waterproofing, the green roof, and a plaza.”

Hydrotech began the project with two things in mind. “We like to say there are two absolutes when you’re doing vegetated roofs,” he says. “One is to keep the structure watertight because you don’t want to be chasing leaks when there’s soil and plants on top of the waterproofing. The second is to make sure that your vegetation thrives despite a rooftop being a harsher environment.”

To ensure the structure is watertight, American Hydrotech uses an initial layer of hot rubberized asphalt called Monolithic Membrane 6125, the same product it’s been using for the past 50 years. “Some of our competitors have experimented, coming to the marketplace with one product only to introduce another product to replace it with, or change their formulation a few years later,” says Dennis Yanez, national marketing manager for American Hydrotech. “I think we’re one of only companies that can say we have a product with such a lasting track record. We’ve installed Monolithic Membrane 6125 on more than 2 billion square feet of roof decks, plazas, and other structures worldwide.”

American Hydrotech adds Gardendrain GR15, a panel with cups and domes that retain moisture while facilitating drainage. “It’s a bit of a balancing act; you want to hold enough moisture to make sure the plants thrive but move the water from heavy rains off,” Rediger says. The engineered soil for this project is LiteTop Extensive Growing Media, designed to be low in organic content and high in mineral content. On top of the soil is a Sedum Tile, a pregrown vegetation tile in a coconut fiber base. After planting, a vegetated roof still requires some maintenance. “There’s always a challenge in that you have to be sure that the landscaper does proper irrigation to ensure that the plants get fully established,” says Rediger, who notes that Atrium Landscape did exactly that, installing gravel walkways and open-joint pavers along the perimeter of the roof.

Also, notably, every element of the vegetated roof—from the membrane to the vegetation and the Glacier White pavers provided by Hanover Architectural Products—came with a single-source warranty, which Yanez says is unique in the industry. “Someone looking for a vegetated roof comes to a company like American Hydrotech because they’re looking for peace of mind and our ability to offer a single-source warranty,” he says. “People are living and working in these structures for the long term, so clients are interested in more than making sure the building is green, which is nice. Waterproofing is paramount.”

Jennifer Costanzo, an architect at STR Partners who oversaw the STEM Academy project, says the school’s sustainable design elements were included to attain LEED Gold status and for the education of the students and the community. The green roof—whose design, product selection, and construction was executed by STR in collaboration with American Hydrotech—is visible from the main communicating stair and several classrooms, and STR together with

Jacobs/Ryan Associates decided to design this area to be a bird habitat. “There is an undulation to the planting surface to provide a change in topography,” Costanzo says. “Birdhouses were installed, and trees that were removed from the site during construction were saved and anchored to the roof to provide other nesting opportunities.”

Rediger is looking forward to visiting the STEM Academy when completed and the roof is in full bloom. “We completed the job last September,” he says. “Our installers have been out to check on it, but I’ll certainly be out to take a look at it in the spring.”