December 28, 2018
by Jim Taggart, FRAIC
Over the past two decades, new engineered mass timber products, systems, and construction techniques have changed the way design professionals think about wood as a building material. Historic perceptions about strength, durability, and fire performance have been overturned by scientific evidence and full-scale testing of prototype structures.
As a result, mass timber has begun to make its mark in the residential and commercial sectors, particularly on Canada’s West Coast. However, the industrial buildings market continues to be dominated by concrete tilt-up and steel frame construction, both of which have a significant environmental footprint. Tilt-up concrete, in particular, has inherent disadvantages as concrete cannot be poured in the freezing Canadian winters and requires a considerable amount of additional work to provide effective levels of insulation.
This article, based on a case study by the Canadian Wood Council (CWC), examines three recently completed industrial buildings in southern British Columbia. All three use engineered mass timber products and systems in distinct ways. Together, they offer insights into how industrial construction might evolve to offer greater environmental performance as well as speed and flexibility of construction at little additional cost over traditional methods. As familiarity with mass timber systems increases, these buildings will become cost competitive with other methods of construction—as is the case in other market sectors.
A 1400-m2 (15,000-sf) prefabrication factory is located in the Village of Pemberton, 32 km (20 mi) north of Whistler, B.C. Completed in 2014, this factory comprises a large high-bay workshop, a mezzanine office area, and a small showroom, all contained within a single rectangular volume. The office and showroom components conform to the international Passive House standard.
In 2009, the manufacturer’s co-owner, Mateo Durfeld, had been responsible for the construction of Canada’s first Passive House building, the Austria House. It served as the Austrian team headquarters during the 2010 Winter Olympic Games in Vancouver. Impressed with this super-insulated, prefabricated kit-of-parts method of construction, Durfeld continued to promote the Passive House approach as a way to decrease the environmental impact of buildings. As demand increased, he saw the potential for scaling up his operations with the construction of a larger manufacturing facility on a budget meant for tilt-up concrete buildings.
Durfeld recognized his building would provide a better working environment for employees and have enhanced marketing value if it embodied the principles of Passive House: low energy use, healthy materials, and sustainability on a life-cycle basis.
The integrated design team led by Hemsworth Architecture concluded these criteria favoured wood and wood byproducts as they are natural, nontoxic, renewable, and either recyclable or biodegradable at the end of their primary service life. Analysis also determined that the choice of wood could reduce the related carbon dioxide (CO2) emissions by about 971 tonnes (1070 tons) when compared to a similar concrete building, and 306 tonnes (337 tons) compared to a steel structure (CO2 production values were obtained from www.co2list.org.). The challenge was to design a wood building to deliver these benefits at a competitive price.
The main structure of the building consists of Douglas fir post-and-beam frames, running east to west across the building and set 6 m (20 ft) apart. A central line of columns divides the factory into two bays, reducing the span, depth, and cost of the roof beams. Each beam has continuous ledgers on both sides, providing support and simplifying the installation of roof panels.
The roof assembly consists of prefabricated panels framed with 50 x 254-mm (2 x 10-in.) solid sawn members sheathed with plywood. Dimensionally consistent and easy to secure, the roof panels kept the structure square and stable during erection, eliminating the need for additional bracing. The exterior walls are made from solid spruce/pine/fir (SPF) cross-laminated timber (CLT) panels laid horizontally. The 6-m column spacing optimizes the use of CLT, manufactured to a maximum length of 12 m (40 ft). Each row of panels is offset from the one below, avoiding the continuous vertical joints that can compromise the diaphragm action of the walls.
The CLT panels are exposed on the interior of the building, adding visual warmth to the workspace. Above the CLT, a continuous clerestorey wraps around the structure, providing abundant natural light and views of the mountain in all directions. The structural engineers at Equilibrium Consulting designed steel cross-bracing to connect the roof and wall diaphragms with minimal obstruction of sightlines.
The building exterior is finished in horizontal 50 x 102-mm (2 x 4-in.) fir and larch boards, chamfered on two edges and preassembled into panels. The boards were laid up in a jig to vary the spacing between them in a controlled manner. Vertical backing members were then attached to facilitate installation of the panels.
Varying the openness of the screens enabled the exterior appearance to remain consistent, while allowing each façade to respond to its own solar orientation. On the south and west façades, the slats over the clerestorey windows are closely spaced to provide shading, while those on the north and east façades are more open to maximize views. Additionally, the cladding is left unfinished to naturally weather over time.
The office and showroom spaces are designed to the Passive House standard. Using an airtight, double-walled system and high-performance wood windows, the envelope was optimized to reduce the energy required for heating and cooling. A high-efficiency heat recovery ventilator (HRV) provides a constant supply of fresh air to the office, thereby creating a healthier work environment.
A biomass, wood-fed boiler uses waste from the manufacturing process to provide the heat distributed to the plant through an in-floor radiant heat system. This creates a solution for plant waste while supplying the building with a carbon-lean heat source. As a single-storey building with conforming mezzanine, the structure is permitted to be of heavy timber construction and does not require additional fire-safety measures.
UBC Campus Energy Centre
The University of British Columbia (UBC) Campus Energy Centre (CEC) supplies the new hot water district energy system serving more than 130 buildings on the school’s Vancouver campus. Completed in 2015, CEC replaces a steam-based district heating system dating back to the 1920s. Since it operates more efficiently, CEC has reduced the overall energy consumption on the campus by 22 per cent.
A low-carbon solution
With its large owner-operated real estate portfolio, UBC is concerned not only with the initial cost of its buildings, but also their overall life-cycle performance. Life-cycle assessment (LCA) considers both the embodied and operating energies of buildings, together with a wide variety of other potential environmental impacts from the structure.
With several innovative mass timber structures having been completed—the latest being Brock Commons Tallwood House—UBC’s team is well aware of the advantages of building in wood, including carbon storage, low embodied energy, durability, and recyclability. All of these factors contribute to superior life-cycle performance.
The 1860-m2 (20,000-sf) facility includes an 18-m (60-ft) high boiler room with a mezzanine as well as a two-storey office and administration area with standard ceiling heights. Juxtaposing these program elements creates a stepped cross-section. When combined with the multiple penetrations of the building envelope for intake ducts and exhaust flues, this cross-section could have resulted in a disparate appearance, at odds with the surrounding buildings.
To unify the design, the architects at Dialog devised an exterior screen of zinc panels, supported 0.9 m (3 ft) off the building on a light-gauge steel frame. The screen was manipulated to provide transparency and weather protection as well as announce entry points. The solid panels are perforated at certain areas for air intake louvres and other service penetrations. On the west elevation, the screen rises above a large area of glazing to reveal the inner workings of the boiler room.
A hybrid structure
Also revealed through these windows is the primary structure of the boiler process area: a Douglas fir glued-laminated (glulam) timber post-and-beam frame with infill walls of seven-ply, 225-mm (9 ½-in.) thick CLT panels. The sloping roof is also constructed using CLT panels spanning the full width of the space.
The 18-m (60-ft) high SPF, CLT walls create a continuous enclosure around the mechanical equipment, giving the vast space a sense of warmth unusual in an industrial building. All materials were sourced in British Columbia and fabricated in Penticton.
The apparent simplicity of the structure is the result of innovative details devised by structural engineers Fast + Epp. While the CLT walls of the boiler room appear continuous, the height of the space exceeded the 12-m (40-ft) maximum length of panels currently available. This necessitated the stacking of two panels, one on top of the other, above and below a horizontal glulam beam. To maintain visual continuity of the exposed surface, the panels are machined with a half-lap profile, thereby concealing the beam and creating a neatly mated joint. Where loads are greatest, the glulam beams and columns are replaced with steel members.
The CLT wall panels are notched to accept the glulam beams and designed to resist both the dead load of the roof and the lateral loads imposed by wind and seismic forces. On the west side of the building, where the CLT wall panels are omitted to permit views into the boiler room, roof panels are supported on a glulam beam. The connections between the panels are made using pairs of long stainless-steel screws, set at opposing 45-degree angles. This enables both walls and roof to act as diaphragms. The sloping roof of the boiler room is divided into three sections. The steep mid-section is supported by an inclined hybrid wood/steel truss, concealed from below by the CLT ceiling. CLT was also used for the walls of the administration offices, although the electrical room below—requiring a two-hour fire-resistance rating—is constructed in concrete masonry.
The structure of CEC is pragmatic, employing different structural materials as dictated by function. In comparison to an all-steel equivalent (the construction type most commonly employed for this kind of building), the hybrid wood system reduces the overall construction carbon use by 88.3 tonnes (97.3 tons).
With its exterior cloak of zinc and glass, the building fits comfortably into its campus context, while the exposed wood interiors create a warm and inviting environment for employees.
A Canadian mass timber design-build firm constructed a new fabrication plant in Abbotsford, B.C. The 4600-m2 (50,000-sf) plant includes two visually connected but structurally separate buildings—a 36.5 x 109.5-m (120 x 360-ft) warehouse and workshop space and an L-shaped administration facility.
A kit of parts
Constructed in just five days, the warehouse consists of prefabricated ‘tall wall’ panels, each measuring 3.6 m (12 ft) wide and 9 m (30 ft) high. The roof panels are 13.6 m (2 ft) wide and 19 m (63 ft) long, spanning between the perimeter walls and a central longitudinal glulam beam, and are constructed with glulam edge beams, bridged laterally by solid-sawn joists. The wall panels have laminated strand lumber (LSL) studs.
All the panels were factory finished with plywood sheathing inside and out, fibreglass insulation, and (in the case of the wall panels) an exterior moisture barrier. They were delivered by truck and lifted directly into place. The wall panels carrying the roof loads at the perimeter of the building were kept vertical with temporary shores until the roof panel was installed, stabilizing the structure.
The roof panels were connected in the field with a second layer of plywood, laid in a staggered pattern overlapping the joints between panels. Glued in place, the two layers of plywood create a continuous diaphragm, transferring lateral forces to the vertical structure and hence to the ground. The central glulam beam, on which the end of the panels bear, is supported on glulam columns at 7.2-m (24-ft) centres. This divides the interior into two rectangular spaces. One is dedicated to custom fabrication projects and the other is used to manufacture dowel-laminated timber (DLT) panels. The large column spacing permits the passage of lifting equipment and prefabricated assemblies.
Engineering innovations for elegance and economy
This apparently simple building contains numerous innovative engineering solutions, designed to make the structure more efficient and economical. For example, the end wall contains two large openings, a feature normally requiring the addition of cross-bracing elsewhere in the building. Instead, the project engineers designed the shallow sections of wall above the doors as box beams. Since these beams contribute to the overall lateral resistance, additional bracing was not required.
The glulam edge beams supporting the roof panels have a curved profile for performing multiple functions. It follows the shape of the bending movement diagram and is thicker mid-span (where the forces are greatest and thinner at the supports where these forces are lowest). This saves material and cost. It also creates a slope in the roof to promote drainage.
These efficiencies, combined with a comprehensive application of prefabrication techniques and the speed of construction, resulted in a structure delivered at a cost comparable to that of a tilt-up concrete or steel frame equivalent.
Like nail-laminated timber (NLT), DLT consists of solid-sawn lumber fastened together face-to-face to make a solid panel. However, the fabrication of DLT is a mechanized process in which the boards are first milled, then compressed together by a machine. Holes are drilled through the multiple laminations, and kiln-dried dowels are inserted. As these dowels expand to reach their equilibrium moisture content, a strong mechanical bond is achieved.
Despite this bond, the dowels simply enable the multiple laminations to be handled as a single panel. They do not contribute to its strength. DLT panels of up to 18 m (60 ft) are possible using finger-jointed material. Since DLT panels contain no nails or screws and only miniscule amounts of glue, they can be easily worked or modified with hand or machine tools.
Although different in their design and execution, these three buildings share a common theme. Each embodies the values of the organization commissioning them and, in the case of the Whistler and the Abbotsford manufacturing facilities, built them as well. In a sector of the construction industry where economy and utility have long been the sole drivers of design, these projects add other criteria. They are all healthy and attractive workplaces supporting employee well-being and demonstrating good design has a valuable role to play in every aspect of life.
Jim Taggart, FRAIC, teaches wood design at the British Columbia Institute of Technology (BCIT) in Vancouver. He is also the editor of Sustainable Architecture and Building Magazine (SABMag) and the author or editor of more than a dozen books, including the award-winning Toward a Culture of Wood Architecture (2011). Taggart has also lectured extensively on the role of wood in contemporary architecture throughout North America, Scandinavia, and Australasia. He is a Fellow of the Royal Architectural Institute of Canada (RAIC) and the recipient of the 2012 Premier of British Columbia’s Wood Champion Award. He can be reached at email@example.com.
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