Integrating mass timber in low-rise construction

Fast + Epp's head office in Vancouver is built on a mass timber structure.
Fast + Epp’s head office in Vancouver is built on a mass timber structure.Photos ©Michael Elkan Photography/courtesy Fast + Epp.

By Jim Taggart

With operating energy reductions now incentivized by Passive House Canada and zero-carbon building programs, alongside incremental improvements mandated in legislation such as the BC Energy Step Code, increased attention is being given to the embodied carbon in buildings. In this regard, mass timber products and systems offer reduced carbon impacts, shorter construction times, and enhanced building performance. In British Columbia, design and construction professionals have embraced technologically advanced mass timber as a new paradigm for low-rise commercial construction.

Mountain Equipment Co-op (MEC) flagship store

In Vancouver, MEC’s new store uses cross-laminated timber (CLT) and glulam as part of a holistic approach to sustainable design. MEC had retained Proscenium Architecture + Interiors of Vancouver and Aedifica Architecture + Design of Montreal for a rebranding exercise to integrate its corporate values with the architectural expression of its stores.

Marking the southeast entrance to Vancouver’s Olympic Village neighbourhood, both MEC and the City of Vancouver wanted this project to be special. Counter to the prevailing trend, it was agreed to down-zone the site, so the store itself would be highly visible, rather than forming the podium of a high-rise structure.

The result is a striking wood and glass structure with 5,730 m2 (61,700 sf) of retail and office space, expanding more than three stories, with three levels of parking below grade. Below-ground loading was also required, as the lane at the north side of the building is considered a secondary street and has townhouses facing it. While physically terminating the mid-block lane, the building responds with a glass wall, providing views to the interior atrium, a linear, double-height space around which the store is organized.

The store entrance is on the south side, beneath a projecting CLT canopy that extends the length of the building. The canopy is supported on glulam columns lifted off the sidewalk on concrete plinths as protection against weather. At ground level, the elevations facing the street are predominantly storefront glazing, making this a bright and engaging “gateway” building.

On the upper retail level, the south elevation is split by the glazed atrium, while the west elevation includes a perforated metal mural. Next to the mural, a wide Corten steel scupper guides water from the green roof into a bioswale planter at street level, before discharging it into nearby False Creek.

The interior of the store is bright and airy, extending out to either side of the central daylit atrium. The glulam post-and-beam structure and CLT floors are exposed. An open steel staircase connects the floors, while steel bracing elements contribute to the lateral system. With its carefully routed mechanical and electrical systems, the esthetic is industrial, softened by the warm tones of the CLT display systems and the colourful products showcased.

The third-floor office has a smaller footprint than the retail floors, with setback from the building perimeter creating the opportunity for areas of green and blue roofs. On this level, the wood structure remains exposed, but the building services are run within a raised floor system, finished with concrete tiles to meet the required 45-minute fire resistance rating.

The rectangular site is approximately 62 m (203 ft) in width and 36 m (118 ft) in depth, it is flanked by 2nd Avenue on the south side and Quebec Street on the west. The underground parking garage is of concrete construction, with its 275-m (10.8-in.) thick roof slab becoming the ground floor of the mass timber building above.

The atrium creates an interconnected floor space requiring sprinklers and a smoke curtain. Rather than using glass curtains, the glulam beams at either end of the atrium were increased in depth to match the longitudinal beams, creating the continuous barrier required by the BC Building Code (BCBC) as a smoke curtain or draft stop. The large size of the atrium necessitated an alternative solution, as did the proprietary firestop system used to seal penetrations through the CLT structure.

The structure

Structural engineers Fast + Epp designed the gravity system as a glulam post-and-beam frame, with CLT floor panels spanning between beams. While the structural grid for the retail floors is rectangular and most often measures 7.5 m (24.6 ft) east to west, the spans vary considerably in the north-south direction. The longest is 8.4 m (27.5 ft), requiring beams that are almost 1 m (3.3 ft) in depth. The glulam columns vary in size, the largest being around the atrium. With the requirement for a 45-minute fire resistance rating, all the glulam elements are oversized to include a charring layer of approximately 30 mm (0.7 in.) on each exposed surface, protecting the integrity of the structural section within.

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