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In a move that is becoming less rare, developers across North America are looking to wood-frame construction as a cost-effective and swift way of building mid-rise structures. Long-standing misconceptions and regulatory burdens have historically limited the use of wood in multi-level Canadian buildings, but to the delight of the development industry, recent legislative amendments are finally making wood-frame construction a viable alternative to traditional concrete and steel structures. British Columbia and Ontario have both amended their building codes to permit six-storey wood-frame buildings, while Quebec is doubling down, upping their limit to 12 storeys.
We talked with Toon Dreessen — President of both Dreessen Cardinal Architects Inc. and the Ontario Association of Architects — who shed some light on the benefits and drawbacks of wood-frame construction.
"One of the decisions in planning a project, and this speaks to the skill of an architect, is figuring out early on in a design what possible structural systems or building form will be contemplated," said Dreessen. "You can build a two-storey apartment building out of concrete if you wanted to, but it wouldn't be cost-effective. Thinking about what the options are and what makes the most sense is part of the job of the architect. What are you permitted to do and what's best for the building?"
While concrete and steel have traditionally been the go-to building materials, site constraints can make constructing these types of buildings problematic. "For a mid-rise building in the six- to ten-storey range, often what it comes down to is a question of steel versus concrete," said Dreessen. "It's a question of understanding the availability of local trades, the capacity for the site to carry the building load, and how the building will be built. Concrete needs places for the formwork to come out, access for concrete trucks to pull up and do the delivery, and locations for cranes. Thinking about the logistics will set the stage for what materials to use."
Dreessen explained how site attributes inform an architect's decision to choose the appropriate framing structure by citing one of his firm's projects in Ottawa, 360 Lofts. "We chose to go with wood because the site was very small and extremely tight. We had nowhere to lay down materials and formwork, no place for a tower crane, and every minute we occupied the street and sidewalk with construction equipment was expensive. We went with wood so that they could deliver to the site only the lumber they needed for that particular day." Though the building's structural supports are hidden from the public, a glulam timber column at the corner signals to passersby that it was indeed built using wood. A projecting volume at the third floor is clad in a different colour and material, helping the building stand out from its neighbours.
Dreessen noted that wood-frame buildings are generally less expensive, but maintain similar durability and soundproofing qualities as concrete. Dreessen also challenged the perception that completed wood-frame buildings are less safe than concrete structures. The presence of sprinklers and fire alarms — not the type of building material — has proven to be the key safety indicator. However, it's when wood-frame buildings are under construction that safety issues may arise. "Part of the problem with wood-frame construction is that the fire separation is driven by the drywall applied to it, but you can't apply that drywall if it's pouring rain or it's really cold because it's subject to moisture, mold and damage. In a concrete building, you can strip the formwork and keep going. The construction site is non-combustible while construction is going on."
As wood-frame construction is often at the mercy of uncontrollable weather conditions, delays can and do happen. "In a wood-frame building, you maybe have to wait until the roof is on and it's ready to be tarped off before you can start making a decent fire separation, because in the meantime, it's all exposed wood," said Dreessen. "It poses a sequencing problem for the contractor. The framer has to do his job, the drywaller has to install the drywall, and then the plumbing trades can start. Then the drywaller has to come back and put bulkheads around everything. It's a sequencing struggle that has to be resolved with the help of a good general contractor, construction manager, and owner."
Despite the challenges posed by wood-frame construction, high-quality products do exist to make the process more workable and less messy. "I think once you've hit four storeys and higher, you really want to think of engineered lumber and engineered timber construction. Cross laminated timber is something that is a real game-changer in the wood multi-unit residential market because it's much more prefabricated," explained Dreessen. "You're preassembling panels of wall and sections of flooring, and then they're arriving to the job site ready. It's a much quicker assembly process and it's more non-combustible."
With recent building code changes coming into effect across North American jurisdictions, Dreessen believes mid-rises will be a much more feasible building option for both developers and the wider community. "I can think of neighbourhoods in Ottawa where I'd love to see that four- to eight-storey range of construction. It's the sort of thing that communities I think would be supportive of. You've added a mechanism to the market that is in the right range. There's so many issues associated with insurance, constructability, sequencing, and weather, so you get to a point where the developer doesn't want to build as they're not interested in that scale and it's not worth it." The savings resulting from a cheaper form of construction would also likely be passed onto consumers, lowering the cost of housing.
Builders have differing opinions on the environmental qualities and benefits of wood-frame construction. "There's arguments both ways," said Dreessen. "From the perspective of wood, especially engineered wood, that is a real resource. You cut down a tree and you plant another one. The tree is all carbon. You cut it down, sequester that carbon inside the building, plant another tree, extract carbon from the atmosphere and you've got more trees. The engineered product has very little waste because the sawdust can be chewed up into something else."
On the opposing end, one of Cardinal Dreessen's current residential projects, Joyce House, uses concrete. "Something like Joyce House could be built in wood because it's six storeys and that's permitted under the building code in Ontario, but when we look at the building form in terms of its shape, there's changes in floor plates that are a bit harder to do in wood," said Dreessen. "Something like concrete, which is liquid in its original state, can flow into and be used to shape things differently."
Situated in Ottawa's Centretown neighbourhood, Joyce House contains a number of interesting features, not the least of which is a pair of dedicated car elevators that will transport vehicles between the street and the underground parking garage. Condominium residents in the building — which is targeting LEED Silver certification — can enjoy a common room and second floor terrace equipped with a fountain and patio space. "It adds visual interest to the street and provides a place for people to get together in a social setting and engage with the things that happen on Bank Street," said Dreessen. "You can watch as the Santa Claus Parade goes by."
The limestone and dichromatic brick exterior acts as a seamless extension of the historical streetwall. It also provides the insulating properties that modern all-glass buildings cannot achieve. "Glass is a great material and we've made huge strides in its technical qualities but a really good window is still a quarter or a fifth of the insulating value of a wall," said Dreessen. "The energy use that goes into an all-glass condominium is just enormous because you're constantly fighting the cold. By having punched windows, it becomes more possible to have greater insulation value and reduced energy load. That helps make the building more cost-effective over the long run."
Whether wood, concrete or steel-framed, Dreessen believes that longevity is a crucial component of architecture. "We look at the context of what the building will be and design something that is durable and maintainable. I want to be proud of it and say 'I did that,' so the building has to last. Choosing materials that are durable, high-quality, and express different functions is worth it." Joyce House is targeting a spring 2017 delivery, so we'll have to wait until then to see Dreessen Cardinal's latest architectural vision come to life.
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