Enthusiasm builds in Canada for multi-storey structural wood buildings
Despite historical fire and structural safety concerns, the modest, tall wood buildings movement of the last few decades is picking up steam in Canada.
To provide a framework for architects and builders, the Government of Ontario published a (free) guide in October 2017, Tall Wood Building Reference: A Technical Resource for Developing Alternative Solutions under Ontario’s Building Code.
The technical resource has two main sections: Fire Safety and Structural Design. These two major topics are normally of most concern during design and review of tall wood buildings and are at times interrelated, states the reference. “Thus, it is expected that design teams and building departments will work together at the early stages of design since structural decisions can affect fire performance and vice versa. The sections go into detail on aspects of compliance, methods of analysis, methods of design and the expected performance requirements for fire and structure. Other topics such as thermal performance, acoustic performance and constructability are covered in other references as noted throughout this technical resource.”
FPInnovations of Pointe-Claire, Que., a Canadian primary and secondary wood manufacturing research organization, has had its 2014 Technical Guide for the Design and Construction of Tall Wood Buildings in Canada for sale since 2014.
What is a tall wood building? In Ontario, according to the provincial reference guide, “a tall wood building is defined as a building over six storeys that uses wood for its structural system and is built using mass timber construction. Mass timber refers to large-dimension solid lumber, glued-laminated lumber, cross-laminated lumber or other large-dimension wood products as opposed to conventional stick-frame construction typically used in low-rise and mid-rise buildings.”
British Columbia and Quebec have also approved designs and issued building permits for buildings that exceed the six-storey limits using other mechanisms in their building codes.
Building tall in wood is not a new phenomenon, according to FPInnovations. In fact, it says, Canada has a history of constructing tall wood buildings out of heavy timber and brick elements, reaching up to nine storeys.
“In the early 20th century,” states FPInnovations, “with the increase in reinforced concrete and structural steel research and construction, and with growing concerns over fire and durability, the structural use of wood fell out of common use in tall buildings.
“This trend is beginning to reverse, however. In the last few decades, the world has seen a resurgence of mass timber products and systems that are paving the way for tall wood buildings.”
The technical guide from FPInnovations was prepared by a group of experts to assist architects, engineers, code consultants, developers, building owners, and Authorities Having Jurisdiction (AHJ) in understanding the unique issues to be addressed when developing and constructing tall wood buildings that are beyond the height and area limits currently found in the National Building Code of Canada (NBCC).
The Canada guide also provides design and construction teams with the concepts and background to respond to questions that arise when designing beyond the height and area limits prescribed by the NBCC. Mass timber offers the advantages of improved dimensional stability and better fire performance during construction and occupancy, notes the Ontario guide. “Tall wood buildings are not new to Ontario — many such buildings are still in use in Ontario after nearly 100 years in service, however over time, changes to building codes and the introduction of steel and concrete for high-rise construction resulted in a decline in construction of tall wood buildings over the decades.
“But with new wood products and modern means of fire engineering, modern tall wood buildings are now being built in Canada. The new products and the way in which they are pre-fabricated and constructed offer tremendous opportunities to improve quality and speed of construction for buildings in Ontario.”
One tall wood building construction project that stands above the rest in recent years is the Brock Commons Tallwood House completed in 2017, an 18 storey, LEED Gold target, 404-bed student residence building located at the University of British Columbia (UBC) in Vancouver.
And coming soon at just seven storeys — one storey above the provincial code tall wood definition — 77 Wade Avenue, located in Toronto, Ont.’s Bloordale Village, will be a prototype for a mid-rise (between six and 10 storeys) office building, using a hybrid structure including mass timber.
Designed by Toronto-based Bogdan Newman Caranci (BNC), the inherent warmth of exposed wood structure will be showcased through the use of composite mass timber, concrete and steel structural assemblies to create highly desirable environments for today’s office occupants, according to BNC. “Unlike the construction of 20th century post and beam buildings,” states BNC, “construction of 77 Wade optimizes the use of a mass-timber hybrid structural system by way of pre-fabricated components and just-in-time delivery and construction practices to achieve spans akin to traditional concrete and steel superstructure projects.”
The approach to the building is unified with an origami geometry soffit and organic front entry, retail and flexible collaboration spaces, states BNC. Perched above the form is a wood canopy that creates shading for the outdoor amenity/social space, it adds.
Tall wood buildings lend themselves to creative design choices in millwork and furnishings, such as in the forthcoming 77 Wade construction. The description of Tallwood House at UBC by Acton Ostry Architects of Vancouver, B.C., certainly provides a glimpse of this potential:
“A prefabricated facade, arranged in a pattern of vertical striations, features pre-installed windows and cladding consisting of 70 per cent wood fibres. A metal cornice crowns the building. A CLT canopy runs the length of a curtain wall base, which reveals the warm wood finishes of amenity spaces within.
“Elevator lobbies are clad with the same material as the exterior. Hallway finishes include natural wood doors and a palette of rich umber and ochre accent finishes.”