Architectural zinc roofing considerations

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A steeply sloped, zinc-clad roof is the architectural focal point of a new, open-air pavilion at the Trillium Park and William G. Davis Trail at Ontario Place in Toronto. The opening of the park and waterfront trail marked the first milestone of the province’s plan to revitalize and transform the iconic landmark into a vibrant, year-round attraction.

Approximately 600 m² (6458 sf) of proprietary blue-grey zinc, double-lock standing seam panels clad the four sections of the steep roof. The 0.8 mm (31 mils) zinc panels included a factory-applied backside coating, which reduces corrosion arising from design, construction, and workmanship defects. This coating frequently is used for standing seam and interlocking tile roofing applications.

The panels were installed by Semple Gooder Roofing Corporation in Toronto.

“The steep pitch of the roof, as well as some complicated intersections of panels, was definitely a challenge,” said Peter Sjourwerman, manager of Semple Gooder’s architectural cladding division. “But we have been working with zinc for more than 20 years and can pretty much fabricate anything. For example, we custom-fabricated a radius ridge cap with concealed fasteners for the pavilion in our shop and made all of the custom flashings onsite.”

Sjourwerman is a believer in zinc as a long-lasting material.

“It may last more than 100 years, but it definitely needs to be installed properly,” he said.

Design for Trillium Park was led by landscape architects LANDinc of Toronto in consortium with a diverse multidisciplinary team, including West 8 of New York and Blackwell Structural Engineers of Toronto.

“The pavilion sits at the end of a performance lawn as an object in space that is meant to create some curiosity and wonder and be a potential meeting place for small events and gatherings,” said Patrick Morello, principal of LANDinc.

Bruce Gilchrist, project manager and designer with LANDinc, continued, “No material other than zinc was considered for the roof of the pavilion. We sought out zinc for its naturally weathering patina, which will develop over time.”

The park pavilion’s design also included the use of heavy timber to reflect the industrial connections to natural materials at the turn of the 19^th century. An ongoing challenge was to sustain an open gathering space within the pavilion amid the wind forces imposed on the roof faces from Lake Ontario.

“LANDinc architect-of-record Christopher Wallace explored numerous structural options to achieve a limited number of columns that connect to footings embedded in bedrock,” Gilchrist said. “Due to the intersecting roof forms created by Adriaan Geuze of West 8, the greatest challenge was co-ordinating the work of each trade at the connection points. A virtual and physical 3D printed model was constructed by LANDinc and further evaluated to assist in the fabrication of each material section on the structure.”

Construction of the pavilion was completed by A-Con Construction of Bolton, Ont., working under Toronto-based general contractor (GC) Urbacon. The project team’s design and construction to revitalize Trillium Park and William G. Davis Trail at Ontario Place has received numerous accolades, including a 2018 National Award of Excellence from the Canadian Society of Landscape Architects (CSLA).

The opening of the park was the result of a three-year design consultation process, which included public workshops and consultations. The high-profile project was managed by Infrastructure Ontario and the ministry sponsored by the tourism, culture, and sport ministry.

At the opening celebration, the then minister of tourism, culture, and sport, Eleanor McMahon remarked, “This new public park and trail brings the beauty of Ontario’s natural landscapes to the heart of downtown Toronto. In a city this size, it is important to have resources like this one for people to enjoy.”

William G. Davis, former Premier of Ontario (1971–1985), added, “I am pleased to see a new era begin for Ontario Place and I am honoured by the beautiful trail that now bears my name. When Ontario Place opened in 1971, it was designed to be a place that everyone in the province could enjoy—a place that would show Ontario’s potential. Forty-six years later, that potential is our reality—a province that is inclusive, innovative, and a place that people from around the world are proud to call home. Once again, Ontario Place will be a gathering spot for the people of this province to come together.”

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Completion of a reroofing project at Vancouver’s historic Christ Church Cathedral[7] marked the culmination of a massive four-phase, 22-year renovation plan. The cathedral—built originally in 1894—was the city’s first church, and began with a cedar shake roof. Through the years, various additions and modifications were undertaken, but none contributed significantly to the historic structure’s long-term sustainability.

In 1995, a formal plan was implemented to make the cathedral structurally sound and meet seismic stabilization requirements. Esthetic and acoustical upgrades, along with basic functional improvements, were also included in the multi-phase plan.

Replacement of the roof—the final stage of the extensive renovation project—became something of a modern marvel in Vancouver. The entire building was completely enclosed in a massive scaffold and covered with a giant tarpaulin to protect it from the weather as the existing roof was removed. The scaffolding reached 30 m (100 ft) high to allow use of a travelling gantry crane for moving materials to all areas of the roof.

Approximately 1115 m² (12,000 sf) of proprietary blue-grey zinc panelling was installed using a traditional batten-seam profile. Installation of the panels was done by TEK Roofing of Vancouver, B.C.

“I am an old-school guy, and everything we do is traditional,” said Terry Kellogg, TEK’s president. “The panels are literally all hand-formed. No machines were involved other than our breaks.”

TEK Roofing specializes in the fabrication and installation of natural metals. Its crew on this project ranged from 10 to 20 individuals, depending on the work being done. Kellogg worked alongside his crew for nearly two months of the job, which took nine-and-a-half months in total. TEK spent five months levelling the entire substrate and four-and-a-half months installing the underlayment and zinc panels, focusing on the dormers and other intense detailing for the last two.

A major issue that had to be resolved before the new zinc roof could be installed was achieving a level and true substrate. During the many years since it was originally built, the structure had settled and shifted considerably. Further, the construction methods employed more than a century ago were not nearly as exact as those used today.

“We were surprised at how bad the structure was when we opened the building up,” said Ian Birtwell, a parishioner and volunteer project manager who functioned as liaison with the church. “The connections to walls were very poor, basically gravity connections. That is the way they built in those days. And the roof ridgeline dipped 150 mm (6 in.). We used a laser system to create a computerized 3D model that revealed the high and low spots so that we could get a totally flat roof.”

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Kellogg was quick to give credit to another company involved in levelling the structure, Pacific Building Envelope Maintenance (PBEM).

“PBEM, based out of Vancouver, did a lot of the framing, working under the supervision of our superintendent,” said Kellogg. “PBEM was very instrumental in getting us a level roof. It was a tough, tough job. They added a huge amount of structural steel. We could not have done it without them.”

The general contractor (GC) on the project was Scott Construction Group of Burnaby, B.C. Architectural design was provided by Vancouver’s Proscenium Architecture & Interiors. Renovation of the historic building was deemed a heritage project, and had to meet certain guidelines for approval.

“Good heritage practice requires that the renovation be respectful of original materials,” said Hugh Cochlin, Proscenium’s principal. “We gravitated to zinc pretty early in the process. We wanted a durable material that would last forever.”

Cochlin said the team expects the product to last 100 years or more, adding that “the Heritage Commission quickly approved our use of it.”

Kellogg concurred regarding the lifespan of the zinc, saying “With the pitch of the roof, it is easily a 100-year roof.”

Another interesting attribute of zinc that influenced its selection for the project is its ability to repel moss.

“The cathedral is in somewhat of a concrete canyon with high-rises all around, and thus gets very little sun,” Birtwell said. “The previous roof was moss-covered. We sometimes joked that the moss was the only thing holding the old building together.”

The detailing on the job was complex, with multiple interfacing.

“We had complicated transitions,” Kellogg said. “There was no caulking, no screws—all traditional methods. There were lots of pitch changes and elevation changes that made the installation time-intensive. It was definitely a labour of love.”

According to Cochlin, all of the details were drawn by hand.

“That is definitely old-school,” he said, “but particularly appropriate for a heritage project. We worked closely with TEK Roofing and had many onsite meetings. There was definitely more collaboration with the installer than is the norm today.”

Another major aspect of the final-phase renovation was the addition of a highly anticipated bell spire set atop the existing elevator core. The open glass and steel structure housing four custom-cast bronze bells was the last significant architectural addition to the project. The bells were cast in France, and the bell spire glass features a design by Canadian artist Sarah Hall.

“Completion of the project protects the heritage of this historic and much-loved church,” said Peter Elliott, dean and rector of Christ Church Cathedral.