Metal Architecture Home

Transportation & Aviation

York University Station, Toronto, Canada

From above, York University Station’s roof resembles a boomerang with upturned tips. At ground level, the building undulates with bubbles of glazing in the middle and at its ends. On its concave side, the structure is sunk into the landscape in an amphitheater-shaped bowl where a double-height curtainwall opens the interior to western daylight.

The subway station’s curvaceous massing, free-form roof and undulating exterior are the vision of Foster + Partners, design architect for the project. It is one of six new stations built on a 5.3-mile elongation of Line 1 on Toronto Transit Commission’s subway system, the Toronto-York Spadina Subway Extension.

To make the vision a reality, Bothwell Accurate Co. Inc., roofing contractor for the project, installed five of the six primary layers of materials in the roof assembly. The bottom layer was segmented steel decking, which was covered by gypsum board then a two-ply bitumen system. On top of those three layers, the Bothwell Accurate crews attached a metal sub-framing system of pre-curved hat channels, tracks and studs, which were connected with angle clips at various heights. Radius Track Corp. supplied the metal framing and clips. Under and around the metal framing, a layer of 3-inch-thick, semi-rigid, mineral wool insulation was installed. On top of the metal studs, crews installed thermally broken clips, supplied by Kalzip Ltd. and Kalzip’s Kz65/333 aluminum standing seam roof system.

The metal decking was out of tolerance for the completed roof assembly at some locations. At the same time, the standing seam panels were fixed sizes and shapes. Trevor McGrath, estimating manager for cladding at Bothwell Accurate, says all height differences between the decking and standing seam panels needed to be worked out by adjusting the framing.

“We scanned the as-built roof structure, and we overlaid that with the skin model, which is what the architect did as a 3-D model,” McGrath says. “Radius Track [framing manufacturer] took the 3-D scan and did a color-coded model showing how much the roof was out of tolerance at different locations, how much adjustability we had to do. And then we took that drawing and fabricated the roof structure to make up any differences.”

Radius Track used the 3-D model to design, engineer and fabricate a metal sub-framing system. In all, Bothwell Accurate installed 4,323 feet of 16-gauge G120 galvanized steel 1 5/8-inch-wide, curved hat-channel, 2 1/2-inch-wide, curved track, and 1/2-inch-wide, curved C-stud and stand-off clips.

Bothwell Accurate started installing the roof at the midway point with a double-female panel, and then worked outwards in both directions, McGrath says. The company installed 12,271 square feet in 374 panels of Kalzip’s curved and tapering standing seam roof system. Due to the tapering roof design, the panels varied in width from 16 inches to 8 inches, and in lengths to 35 feet. The metal panels protect the two-ply bitumen system from UV degradation and resist solar heat gain.

To drain stormwater, the roof has a perimeter gutter that runs into the building and exits via the sewer system. At ground level, the perimeter gutter is hidden from view by fascia. McGrath says, “The gutter started off as a steel angle frame, which we then put tapered insulation in, so the insulation thickness changes to cause sloping to the drains, which are evenly spaced apart.”

York University Station’s structure was built with poured-in-place concrete and structural steel. Supporting the free-form roof, a ring beam extends around the entire perimeter.

On the building’s concave side, there is an egg-shaped curtainwall. Bu Josef Gartner USA supplied the curtainwall, and Riverside Group supplied the metal wall panels. Riverside also supplied metal ceiling panels, installed at the two entrances at opposite ends of the station. The project was completed in December 2017.