April 13, 2014
By Werner Hofstätter
In Prince George, B.C., the corner of George Street and Fifth Avenue has been a hive of activity since October 17, 2013—the day the first massive pieces of engineered timber for the Wood Innovation and Design Centre (WIDC) started arriving, launching what is expected to be the tallest contemporary wood building in North America, and one of the highest anywhere in the world.1
Set for completion this fall, the six-storey (plus mechanical penthouse), 29.25-m (96-ft) high structure will showcase British Columbia’s growing expertise in the design and construction of large-scale wood buildings. This project incorporates a unique structural system that uses a wide range of locally manufactured engineered wood products, and is targeting Gold under the Canada Green Building Council’s (CaGBC’s) Leadership in Energy and Environmental Design (LEED) program. The 4600-m2 (49,500-sf) building will be almost as tall as B.C. forests, and will be made up of 1846 m3 (65,190 cf) of various wood and engineered wood materials.
The program for the building will include research facilities, demonstration space, and classroom facilities for the University of Northern British Columbia’s (UNBC’s) much-needed new master’s programs in wood engineering, as well as office space for commercial tenants. The occupancy will consist of:
Why build with wood?
The provincial government has invested $25.1 million in the WIDC, creating an estimated 250 jobs during the life of the project. Nurturing new markets for the products made by the 19,000 British Columbians in the forest industry and 30,000 in wood products manufacturing is considered a priority.
The choice of products used to build, renovate, and operate structures also has significant environmental effects. When specifying any materials, it is important to consider their impacts over the lifecycle. Wood products have less embodied energy, are responsible for lower air and water pollution, and have a lighter carbon footprint than other commonly used building materials. With growing pressure to reduce the carbon footprint of the built environment, building designers are increasingly being called on to balance functionality and cost objectives with reduced environmental impact. Wood can help to achieve that balance.
There is also growing evidence exposed wood has positive impacts on the health and performance of occupants. A recent study at the University of British Columbia (UBC) and FPInnovations has established a link between wood and human health.2 In the study, the presence of visual wood surfaces in a room lowered sympathetic nervous system (SNS) activation, which is responsible for physiological stress responses in humans. This result opens the door to myriad stress-related health benefits that the presence of wood may afford in the built environment.
The ‘dry’ system
The Wood Innovation and Design Centre design team, led by Michael Green Architecture and the structural engineers at Equilibrium Consulting, opted for a ‘dry’ system. In other words, the only concrete in the building is in the raft slab and under the floor below the heavy mechanical equipment in the penthouse.
Watching the assembly one might conclude the construction process mirrors the installation of concrete forms, except the forms are actually the final structure. This means the steps of concrete reinforcing, pouring, and curing—and removing the forms—are eliminated. Not only does this dramatically reduce the structure’s weight, but it also speeds up construction, reduces traffic congestion, and makes the building entirely de-constructible.
The structure sits on a reinforced concrete raft slab and consists of engineered wood columns and beams, supporting mass timber panels. These components are held together by a combination of embedded metal connectors, external metal plates, and self-tapping screws.
At the foundation, steel connector plates are deeply mitered into the bottom end of the glued-laminated timber (glulam) columns with state-of-the-art, high-strength, self-tapping screws. After careful alignment, the protruding tab is arc-welded to plates pre-mounted onto studs embedded in the concrete raft slab. This connection provides tremendous resistance to lateral loads and uplift.
All the columns and most beams were glulam members provided by the same source, except for the parallel strand lumber (PSL) transfer beams on the first storey, which support the major loads over the open atrium and mezzanine. For ease of installation, the columns and beams arrived on-site with factory-installed, proprietary, aluminum, dove-tail connectors. Erecting the system simply involves sliding the devices into each other until they mate and self-tighten.
The columns stack, end-grain to end-grain, minimizing the potential for shrinkage as most of this occurs perpendicularly, across the grain of the fibres. The top of the column of the lower storey below penetrates the floor slabs, and is connected directly to the column above using embedded steel connectors. Concealing the majority of the device within the wood allows the material’s natural insulating properties to protect the metal in the event of fire.
This is a modern twist on the traditional post and beam designs seen in industrial and commercial buildings built around the turn of the 20th century. Some as high as nine storeys tall, many of these are still in use in Vancouver, Victoria, Toronto, and other major cities in North America.
Mass timber panel technology
The floor and roof diaphragms of those early 1900s buildings were traditionally constructed of gang-nailed dimension lumber, such as 2×8 planks on-edge. These extremely sturdy assemblies were the first examples of what is now frequently termed mass timber panel (MTP) technology.
MTP refers to any wood-based diaphragm that can be used as an alternative to reinforced concrete, for floors, roofs, walls, and cores. Many of these are pre-manufactured to exacting specifications using computer-numerical-controlled (CNC) equipment, with openings, penetrations, and connection details precisely tailored for each individual piece.
Modern mass timber panels come in sizes of up to 3 m (10 ft) wide, 19.5 m (64 ft) long, and 305 mm (12 in.) thick, and in various compositions from a wide range of suppliers. In addition to simple nail-laminated slabs, several glulam manufacturers now offer glued versions of up to 3 m wide. In addition to being used in floors and roofs, nail-lam or glulam mass timber panels are now often used for the timber elevator and stair shafts in British Columbia’s five- and six-storey, light-wood frame residential, mid-rise apartment buildings.
Laminated strand lumber (LSL) panels are made by shredding wood from fast-growing, low-value hardwood logs, such as aspen, birch, and poplar into thin strands. These are oriented for maximum strength and glued together into 2.4 m (8 ft) wide by 19.5 m (64 ft) long ‘billets’ via a steam-injection process. When used in their original wide-sized format, they provide an excellent option for diaphragm applications. Full-sized LSL panels provide structural support and a unique architectural statement in projects such as the North Vancouver Civic Centre, UBC’s Earth Science Building, and the Wildlife Interpretive Centre in Kamloops.3
Cross-laminated timber (CLT) is a large, multi-layered, wooden panel made from dimension lumber.3 CLT is engineered for strength and stability through laminations of different layers placed cross-wise to the adjacent layers. Each panel is then sized and shaped, usually with a CNC machine into a fully articulated construction-ready component. By the nature of its design, CLT has inherent load-bearing strength and can serve as material for both vertical and horizontal assembly applications.
Laminated veneer lumber (LVL) panels are made from ‘peeler logs’ in the same production lines as LVL beams. Engineered to precise design values and with a high strength-to-weight ratio, LVL panels are also suitable for structural wall, floor, and roof applications. With the renewed interest in engineered wood products for diaphragm applications, manufacturers are beginning to position LVL in full sheet format, but the most interesting configurations involve laminating LVL beams side-to-side to make thin, solid, vertically laminated LVL panels, as at the Shoreline by MGA project for Weir Jones Engineering Vancouver.
While WIDC includes only CLT and LVL mass timber panels, many of the installation techniques described below would apply similarly for the other systems.
The solid wood core
The construction team of PCL Westcoast Constructors, supported by John Boys and Company, quickly saw the advantages provided by the solid CLT core panels that form the elevator shaft, stairwells, and vertical mechanical corridor. Panels 2.4 m (8 ft) wide, 12 m (40 ft) long, and up to seven plies thick were used in the core, and registered up to 3538 kg (7800 lb) on the crane as they were quickly lifted into place.
Deeply embedded steel anchor plates on the edge of the panels using the ductile HSK system were arc-welded to plates attached to the concrete foundation. The core will provide complete resistance to lateral loads and uplift.
Edge-to-edge, the CLT panels are connected using lap joints and self-tapping screws. Firestopping was applied between all edges to ensure a seamless connection. The inside corners were reinforced with metal angle plates, once again quickly installed with self-tapping screws.
The entire core will require three tiers of these massive CLT panels to achieve the total 29.25-m building height. The end-to-end connections, where the panels are stacked, are achieved using a combination of lap joints, self-tapping screws, and custom-designed steel hold-down straps.
Fire protection for WIDC is provided through a fully engineered approach, based on charring rather than the more common encapsulation method. This means, rather than protecting the wood structure from exposure to fire by covering it with non-combustible material, the wood is left exposed, but the sizes of all the columns, beams, and mass timber panels are increased. The structural sections are over-sized to provide a protective ‘sacrificial’ layer of wood that will char slowly enough to provide the required fire protection.
Corrugated solid panel floors
One benefit of mass timber floors is they can provide both a structural floor and an exposed ceiling, which can significantly reduce the cost of finishes. However, as the constructors of the 16 other contemporary tall wood buildings around the world discovered, the solid wood nature of the panels can make routing services problematic.
As a result, the Wood Innovation and Design Centre’s floors were designed using a unique ‘corrugated’ system of staggered CLT panels. Three-ply CLT is used as the top layer, supported on five- and seven-ply CLT plates spanning between the glulam beams. With the staggered floor slab design, the distribution of mechanical and electrical systems throughout the building is solved in a new and repeatable way.
Horizontal chases are created between the staggered timber slabs to run services both below the floor and above the ceiling. An acoustic-insulated subfloor system will be loose-laid over the chases with cut-out panels to provide access to these floor trenches. Lighting and fire suppression systems will be run in the ceiling recesses, concealed with a simple, removable wood-slat finish.
The service chases inherent in the structural system offer extensive flexibility for reconfiguring the space for future occupants. Therefore, the need for secondary ceiling finishes to conceal service runs is significantly reduced, saving materials and cost. The wood structure is exposed at the ceiling, providing a beautiful finish that speaks to the purpose and mission of the facility.
The building envelope
Wood also plays an important role in the building envelope. The building’s form is simple and restrained, allowing the beauty of wood to shine through. The building envelope design is a metaphor for bark peeling away from the trunk—‘bark’ on the north side, thick and protective from the cold and elements, thins toward the south sunlight.
The exterior is more opaque to the north and becomes increasingly transparent as one circles the building to the south. This optimizes sun exposure and insulation, tuning the building’s energy performance to the orientation and northern climate. The non-glazed walls are wrapped with high-efficiency structural insulated panels; a sandwich of oriented strandboard enveloping a foam core.
Most of the cladding will be made up of charred cedar siding. Charring wood is a traditional construction practice, employed for centuries in Finland, Japan, and Switzerland. In addition to enhanced pest control and durability, it provides an alternate contemporary palette for wood cladding. The WIDC will be the first significant demonstration of this system for a commercial building in North America.
Even the triple-glazed curtain wall will be a showcase for wood. High-strength LVL elements will be used for all window mullions instead of conventional aluminum mullions—a unique and innovative use of wood unprecedented at this scale.
The finishing touches
As an iconic six-storey wood structure, the WIDC will build on British Columbia’s expertise and global reputation as an innovative leader in wood construction, engineered wood products, and design. It will be a meeting place for researchers, design professionals, product manufacturers, contractors, and others to generate ideas for innovative uses of wood.
Approaching the main entrance visitors will encounter the impressive canopy, supported by yellow cedar posts, that wraps completely around the George Street and Fifth Avenue façades. The canopy and the feature staircase in the double-height foyer were both fabricated from LVL mass timber panels manufactured in Brisco, B.C. Even the interior blinds that control summer heat gain, and the exterior solar-shades on the main level will be wood, as will the mouldings, trim, and cabinetry. In essence, the Wood Innovation and Design Centre will be as close to an all-wood building as possible, the majority of which will be left exposed for the occupants to enjoy.
1 To view live webcams at the WIDC site visit www.unbc.ca/engineering. (back to top)
2 See the January 2012 report, “Wood and Human health,” by David Fell, commissioned by FPInnovations. Visit www.solutionsforwood.com/_docs/reports/Wood_Human_Health_final-single.pdf. (back to top)
3 For more on the Earth Science Building, read the article “Building the Earth Sciences Building at the University of British Columbia,” by Eric Karsh, M.Eng., P.Eng., Struct.Eng, MIStructE, Ing., in the issue of Construction Canada. (back to top)
Werner Hofstätter is the new products and markets advisor for the Canadian Wood Council’s (CWC)Wood WORKS! B.C. program, and a frequent author on the topic of contemporary tall wood buildings. He can be reached at firstname.lastname@example.org.
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