Purported to have the largest wood roof in North America, Calgary's Rocky Ridge Recreation Facility in the city's northwest quadrant is scheduled for completion by the end of 2017 with the facility opening to the public in early 2018.
"The shape of the building with its undulating roof is intriguing. It reflects the rolling hills of the surrounding landscape," explains Trevor O'Brien of PCL Construction, the Rocky Ridge Recreation Facility contractor.
"The building is clad in brass. It will develop a patina and go from bright gold to a more natural brown colour because it's intended to mesh with the surrounding grasslands."
O'Brien is the senior project manager for the Rocky Ridge project, which has an estimated cost of $191 million. He says the building's design team, including GEC Architecture, RJC Consulting Engineers and ISL Engineering, with the City of Calgary as developer, want to represent the natural features of the site, while creating an open-concept building.
Hence, the team decided on a roof made of glue-laminated timbers, or glulam, fabricated by Penticton, B.C.-based Structurlam.
Glulam is "a stress-rated, engineered-wood product comprised of wood laminations, or 'lams,' that are bonded together with strong, waterproof adhesive," Structurlam describes.
"Wood is highly customizable to conform to the curved shape of the roof at a comparably low cost," O'Brien explains, adding that a CNC machine cuts the necessary curves.
Each roof beam is more than 30 centimetres thick. The glulam timbers range in height from 1.5 to 1.8 metres, with the longest dimension being approximately 90 metres.
While the roof of the Rocky Ridge Recreation Facility is wood, the building's vertical components are primarily steel with concrete forming the remainder of the 284,000–square-foot edifice.
"Designers like the esthetic appeal of the wood roof. If it had been built of steel, there would have been more effort into concealing it with drywall and paint. Because we don't have to conceal the wood, however, it adds to the volume of space inside," O'Brien explains.
The recreation facility and its roof have attracted coverage from the media, as well as visits from designers and educational institutions.
"What draws your attention is the roof. How the vertical steel structures tie into the glulam is quite elegant," says O'Brien, adding that atop the glulam is steel decking, which is visible from the building's interior.
He says there are many benefits to working with mass timber, including its strength-to-weight ratio.
"Wood is both the structure and the finish, so there's a lot less work to do after putting it up," he adds.
Furthermore, as the glulam is fabricated off site and delivered ready to install, "there's a smaller fabrication footprint, which saves space on site and allows for more flexibility," as the team doesn't have to wait for the construction site to be available before commencing work.
"Using mass timber can reduce installation time in the field," O'Brien says, "a construction project is won or lost in the field," adding using glulam is akin to "plug 'n' play" when it comes to initial assembly if it is fabricated correctly and ready to receive the hardware.
"None of the bolt holes were drilled on site. Everything came ready."
O'Brien says one challenge the team encountered is that mass timber, which is susceptible to humidity, adds another material element to the mix, "one with a different set of rules and tolerances" than steel and concrete, and they all have to be considered together.
"Further, each beam is at a different angle, a different elevation and of differing lengths which form the roof's varying curvature," he says. "Each piece has its own connection requirements to think about, its own tolerances.
"You also have varying seasonal weather conditions and you have to account for that."
O'Brien adds the site is at the highest point in Calgary and is exposed to high winds.
The installation and temporary bracing plans needed to be well planned out.
O'Brien says "planning is everything" when doing a project of the complexity of the Rocky Ridge Recreation Facility. Moreover, he says, it's necessary to have people on the team who understand mass timber fabrication and construction.