Mass Timber and Wood Framing

New and traditional approaches reduce cost and meet code for mid-rise construction
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Balloon Framing as a Means to Reduce Shrinkage

Designers used balloon framing to prevent shrinkage on this Vancouver Island development.

Photo courtesy of Misra Architect Ltd.

Located on the southern tip of Vancouver Island, the six-story Skyline Condominiums enjoy an idyllic location and postcard views.

Designers used balloon framing to reduce the potential for shrinkage. “Normally, the wood member shrinks approximately 3/8 of an inch per floor for 12 percent moisture in the wood. To avoid that, we used plywood, joist hangers for the joists, and balloon framing,” says Pradip Misra, principal, Misra Architect Ltd. Because wood shrinks to a greater degree across the grain than parallel to grain, it's the horizontal members, such as the sills and joists than can be problematic, rather than the posts and studs. “The joists are hung from the side of the bearing walls. This eliminates the floor shrinkage in the total building shrinkage,” says Steve Hoel, P.Eng., Struct.Eng., principal, JSH Engineering Ltd.

Skyline's location is prone to humidity, seismic activity, and wind. This resulted in more than a few design challenges. Buildings in this area are required by code to withstand the most severe earthquake loads in Western Canada, and there is always a tendency to build with either steel or concrete. However, the design team and the owners went with wood. Wood-frame structures, which have numerous nailed joints, have more load paths and are inherently more ductile than those with a rigid connection—which make them more flexible and allows them to dissipate energy when subjected to the sudden loads of an earthquake. “The mass of the building also contributes,” says Sukh Johal, technical advisor for WoodWORKS!BC. “Wood buildings are lightweight, but perform well structurally.” Since forces in an earthquake are proportional to the weight of a structure, wood-frame buildings that are properly designed and constructed perform exceptionally well. Misra says that mechanical options were also a factor in seismic design, notably “hold-downs,” known as continuous tie rod systems or 1-inch diameter steel bars that extend from the concrete slab to the upper floors. “This is a self-adjusting system to keep all floors intact in the event of seismic forces.”

Wood also offered advantages in terms of cost. Developers, who opted for a six-story structure in response to the increased height allowed in B.C., compared the costs of concrete, steel, and wood in an extensive study. “A concrete-and-steel superstructure ran 20 to 25 percent more than wood, and a structured steel superstructure 12 to 15 percent more than wood,” says Biki Kang of Kang & Gill Construction Ltd. “Wood was found to be the most economical choice.”

 

Platform Wood Construction Brings Affordable Urban Appeal

Photo courtesy of Tien Sher Group of Companies

The Quattro 3 condominium opened in September 2012, the first multi-family six-story building in Metro Vancouver, built from wood. The project used platform framing to increase affordability and occupant comfort. Featuring 164 units from studios to two-bedrooms and one floor of commercial space, Quattro 3 is part of a larger planned community that will include up to 1,900 homes.

While experts say that mid-rise wood frame construction is too new to B.C. to make a definitive statement about the cost competitiveness of wood, what can be said is that based on projects under construction in 2011 the above-grade cost of wood mid-rise construction will reduce costs by ten percent vs. steel or concrete construction. “There's always a difference between concrete and wood in terms of affordability,” says Charan Sethi, president and CEO of the Tien Sher Group of Companies, developers of Quattro 3. “In the Surrey market, concrete units sell for $50 to $75 per square foot more than comparable wood units.” Sethi feels the mid-rise wood building benefits from lower per-unit land costs and construction costs that can then be passed along to the consumer. “We're always looking for ways of bringing affordability to the working class market,” Sethi says.

Sustainability, locally sourced materials, and ease of construction were other factors that drew Sethi to wood. Sethi says, “Construction was completed by our experienced framing crew and on-site staff. The process was efficient.”

Occupant comfort was a prime concern. Noise transmission is a performance challenge in any multi-family building and in wood construction there are several solutions to mitigate sound transmission, including greater mass, increased stiffness, sound-absorbing insulation, resilient metal channels, and structural discontinuity between noise and occupant. At Quattro, 1.5-inch lightweight concrete topping between floors was used for additional soundproofing and robust insulated double 2-inch-x-6-inch framed party wall construction was employed to minimize vibration and sound transfer between homes.

Fire experts maintain that six-story wood-frame buildings are as safe as any other form of buildings. “For a sprinklered occupied building, there is absolutely no safety issue,” Sethi says. According to Len Garis, Surrey's fire chief and president of the Fire Chiefs' Association of B.C., “the fire safety of people living in six-story wood-frame buildings should be equal to the safety in any other building.” Garis was quoted as saying, “These buildings are fully sprinklered and our research suggests to us that in a sprinklered building, a fire is likely to never leave the room of origin, has historically never left the floor of origin in a building. Where the sprinkler system needed to operate to put the fire out, it put the fire out.”9

Quattro 3 makes an ideal introduction to mid-rise wood buildings in Metro Vancouver not only in terms of affordability, but in occupant comfort and safety as well.

 

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Originally published in Architectural Record
Originally published in November 2012

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