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A Striking Presence

The York University Station’s aerofoil roof stands out amongst its landscaped surroundings

York University1 Mcnaward
Photo courtesy of Foster and Partners

The form and details of Toronto’s York University Station’s swooping roof stood out to the award judges, who awarded the project the new metal roofing category winner for the Metal Construction News Building and Roofing Awards. Awards judge James E. Theimer, AIA, LEED AP, principal, TRILOGY Architecture, Redding, Calif., was attracted to its dynamic form, while judge Ryan D. Martin, AIA, NCARB, vice president-director of design hospitality architecture, LEO A DALY, Dallas, notes that the roof just makes sense for the constraints of the materials. Judge Lewis McNeel, AIA, associate, Lake|Flato Architects, San Antonio, called the roof a technical marvel and achievement. “It looks smart and simple,” he says, “even though it’s an extraordinarily beautiful, complex shape.”

Designed by London-based Foster + Partners, along with Arup Canada, Toronto, the 230,090-square-foot station is one of six new subway stations that are part of a $3.2 billion extension of the Toronto-York Spadina Subway line.

The station is located at the east end of the York University Common, where nearly 2,000 buses a day currently serve transit riders. Construction began on the station in 2011, which opened on December 17, 2017.

Complex Curves

Located on the campus’ central axis, the station’s swooping exterior forms two wings, while its striking boomerang roof canopy provides a new front door for the university. James McGrath, partner at Foster + Partners, notes that the designers wanted to make the new subway station the gateway to the university, while remaining sensitive to the formal arrangement of the university’s primary green space, the Harry W. Arthurs Commons. The station is sunk into common, where its entrance is at the base of a landscaped amphitheater. The entrance is sheltered beneath an expansive aerofoil roof canopy covered in highly polished metal, which reflects the movement of people underneath.

The standing seam metal roof from Kalzip Ltd., St. Helens, United Kingdom, flows from one tip of the building to the other in compound curves connected to an undulating perimeter gutter system. The roof structure is centered over the light well, linking the two covered entry wings to create daylit entry pavilions.

The inverted roof assembly and curvilinear geometry are major design elements for the station. “As the buildings surrounding the station allow views to the station roof, we needed a roof that would be a key design feature of the station, but could also withstand the rigors of the Toronto climate,” McGrath says.

Photo courtesy of Toronto Transit Commission

Form and Function

Radius Track Corp., Minneapolis, supplied the light-gauge metal framing sub-system, which provides the tight tolerances required to deliver the geometry of the design and the durability of the performance specification.

Radius Track provided 3-D model verification and coordination with Kalzip. Each supplier custom-shaped its components with data extracted from the 3-D models to provide an 1/8-inch tolerance, precise-fit sub-system to the finished metal skin. They also sequenced delivery for continuous installation by the roofing contractor, Bothwell Accurate Co. Inc., Mississauga, Ontario, Canada.

“The complex geometry of the roof design and the support structure required us to produce 3-D digital models to produce the drawings,” explains McGrath. “We also 3-D printed many models of the roof design to test the geometry and the intersections of various components. We found that the standing seam metal roof was the best solution for our complex roof geometry.”

To achieve a lifetime roof assembly, the inverted roof system was constructed with Radius Track’s Curved-Right sub-system that supported Kalzip’s standing seam panels, which protect the two-ply modified bitumen base layers. The Curved-Right sub-system also adds space between the two-ply membrane and the metal roof for exterior insulation, which eliminates thermal bridging while providing lifetime support and shape for the metal roof panels.

For the project, Radius Track supplied 4,323 feet of its Curved-Right framing system, including its 16-gauge, 1 5/8-inch curved hat channel, 16-gauge 2 1/2-inch curved C-stud and 16-gauge stand-off clips, all in G120 galvanized steel. Kalzip supplied 12,271 square feet of its 65/333 standing seam metal roof, and Colorado Springs, Colo.-based S-5! supplied 1,000 feet of its ColorGard snow retention system.

Designed to meet Toronto Green Standards, the York University Station’s roof features a cool roof coating, giving it high solar reflectance and which absorbs little heat. The perimeter gutter system captures and reduces stormwater runoff into the municipal drainage system by using soft, landscaped areas adjacent to the building runoff areas.

Photo courtesy of Toronto Transit Commission

Natural Light

According to McGrath, the York University Station’s design utilizes natural light to orient station users, similar to the Canary Wharf station in London, and the Bilbao Metro station in Spain. “This allowed us to simplify the movement of people and make the experience of using the station more intuitive and easy to navigate,” he explains.

A double-height curtainwall from Josef Gartner USA, a division of Permasteelisa North America Corp., Burr Ridge, Ill., is glazed on every side creating a light well, filling the concourse with natural light. The station’s exposed diagrid coffered roof structure is supported by V-shaped columns, which maximize the open area.

“The mullioned curtainwall structure spans from a concrete upstand at the base and extends to the roof eaves soffit panels,” McGrath explains. “Structurally, the mullions run through the soffit panels to connect the steel circular section roof ring beam, that sits on four concrete walls.”