Tim-ber!

The Future of Wood in Construction

In the midst of the post-war building boom in 1949, just when steel and concrete skyscrapers reached impossible heights, Egon Glesinger wrote The Coming Age of Wood, published by Simon & Schuster. In it he described the global importance of wood as a raw material and predicted an increased demand for it in the future. At the time, no one took notice. Now they are.

It seems that the First Nations people of North America and the early European settlers knew a thing or two about the value of wood in construction. While some First Nations tribes lived in tepees, many didn’t. The Five Nations of the Iroquois Confederacy, for example, and other eastern North American tribes, built wooden longhouses measuring 80’ by 18’ by 18’ while European settlers built log cabins. In the 19th century, wood was used to construct ornate Victorian residences, complete with intricate carvings and grand staircases, steepled churches, shops, and barns — in effect, every type of structure.

Wood was also used for covered bridges, and while most disappeared due to neglect, that doesn’t have to be the case, as the longest covered bridge in North America, located in Hartland, New Brunswick, proves. Built in 1901, the 1,282 foot (391 m) long wood structure rests on six concrete piers embedded in the St. John River bed, and cars still cross it daily.

In the 20th century, wood was relegated to framing for residential construction and vinyl siding largely replaced wooden clapboards and shingles. Large public buildings were constructed of stone and brick. By mid-20th century, steel and concrete dominated the skyline of cities across North America.

Admittedly, wood had its drawbacks. Stick built houses are flammable; witness the Great Fire of Chicago (1871), the Great Fire of Saint John, NB (1877), and more recently, California homes ravaged by wildfires. Meanwhile the price of lumber continued to rise, but aside from the cost factor, it was deemed not viable for the buildings of the future: multi-family residences, high-rise office towers, and heavy load bearing bridges. It was a relic of the past. Right?

Wrong! New technology has brought wood once again to the forefront of the industry. It presents exciting opportunities, not only for its use as a construction material, but as a means to helping the world meet climate change targets, or so it’s believed.

“In contrast to carbon-intensive concrete and steel structures, whose production accounts for nearly 10 percent of global greenhouse emissions, wood construction can reduce the total carbon footprint by a third,” says a December 2019 article by JLL. “And the warm, inviting aesthetics of wood align well with WELL Building Standards that help firms boost employee productivity and attract talent.”

Rethinking wooden construction
Engineered wood products, such as plywood, particle board, medium-density fibre board (MDF) and oriented strand board (OSB) have become industry staples. But the real game changers are various forms of mass timber, which include chemically densified wood, a process which increases the rigidity and strength of wood; cross-laminated timber (CLT); and glued laminated timber (glulam).

Developed in Austria and Germany in the 1990s, CLT is a multi-layered panel made of kiln-dried lumber, with between three and nine layers of board placed cross-wise to adjacent layers and held together with fire-resistant and moisture-resistant adhesive to create panels of 1.2 to 3 m (4 to 10 feet) in width and 5 to 19.5 m (16 to 64 feet) in length.

Glulam is another type of structural engineered product composed of layers of dimensional lumber bonded together to create posts. Unlike CLT, it can be joined using pieces of different sizes, so that posts or beams to support bridges can be created in lengths up to 40 m (130 feet), with length limited only by the feasibility of transportation clearance.

Chemically densified wood, CLT, and glulam all offer alternatives to structural steel and concrete. Even though engineered wood is more expensive to produce, construction time can be reduced, as wood lends itself to modular construction. An added benefit is that wood buildings have a lower carbon footprint than steel and concrete ones. Moreover, since the late 1990s, large engineered wood buildings have been shown to be commercially viable across northern European countries.

Coming soon to an urban landscape near you
In 2012, 43 years after Egon Glesinger wrote his seminal work about the coming age of wood, Vancouver-based architect Michael Green wrote The Case for Tall Wood Buildings, a case study on using these materials for buildings as high as 30 floors. And this time, the industry in North America did take notice. In fact, in 2021, MGA, the firm Green co-founded with Natalie Telewiak, was chosen as the Best Firm in North America by Architizer Magazine.

One of MGA’s outstanding designs is the T3 Minneapolis building, a timber, transit, and technology development and the first major, multi-story office building to be constructed of wood in the U.S. in the last 100 years. Completed in November 2016, the Certified LEED Gold building uses only structural material from renewable resources. The seven floors comprise 224,000 square feet of space, 11-foot high exposed timber beams, and 3,600 cubic meters of wood, intended to sequester about 3,200 tonnes of carbon for the life of the building.

Recognizing the potential for engineered wood products to revolutionize the construction industry while contributing to the reduction of greenhouse gas emissions, the Government of Canada, between 2013 and 2017, invested $5 million through the Tall Wood Building Demonstration Initiative (TWBDI) to demonstrate the commercial viability of tall wood building construction. With this assistance, two landmark buildings were completed in 2017.

The Origine building in Quebec, at 13 storeys and composed of Black Spruce engineered wood, was the tallest all-wood condominium building in North America at the time, while the Brock Commons Tallwood House student residence at the University of British Columbia, at 18 storeys, was the tallest hybrid (it uses some steel) wood building in the world when it was completed.

What is significant about these buildings, other than their size and the proof that wood is indeed viable for structures of this magnitude, is that they were instrumental in making changes to building codes, allowing construction of tall wood structures to move forward. For example, the Origine building which was constructed in only five months (December 2016-April 2017) took over two years in the planning stages to prove it could meet the Quebec construction code, which until then restricted wooden buildings to heights no higher than four floors.

This opened the door for other wood structures such as the Abora project in Montreal designed by Provencher Roy Architects and completed in 2019 (see Building Sustainability into Every Detail, Construction in Focus, June 2021). While it’s not the tallest wooden structure at five floors, the three-building residential complex measuring 597,560 square feet was the largest in the world in 2019 and still is the largest in Quebec.

That same year, 2019, the International Code Council approved tall wood structures up to 18 floors as part of the 2021 International Building Code (IBC) which had previously been approved for six. While some provinces and states opted to wait until 2021 to begin construction of tall wood buildings, others including British Columbia, New Jersey, and Oregon (where Michael Green has designed more buildings) didn’t wait and amended their codes to permit 12-storey wooden structures, with the National Building Code of Canada following suit in 2020.

Following the success of the TWBDI, the Government of Canada pledged $39.8 million over four years (2017-2021) through the Green Construction through Wood (GCWood) program to encourage the use of wood in non-traditional construction projects for tall wood buildings, low-rise non-residential buildings, and bridges, with the aim to position Canada as a world leader in tall wood construction and the low-carbon economy.

The first project to be completed, with an $887,000 investment from GCWood and $17 million from the province of Ontario, was the mass timber Duchesnay Creek Bridge which connects the City of North Bay and the Nipissing First Nation in northern Ontario. The 93 meter long (305 foot) 3-span bridge, composed of glulam girders and arches and reinforced concrete and steel, opened in August 2021, replacing the former wooden truss bridge built in 1930.

The second GCWood assisted project involves a $4.1 million investment in an estimated $134 million project to construct a landmark, futuristic building on the lakefront campus of George Brown College in Toronto. Expected to open in 2024, the academic building will use 3,000 cubic metres of wood resulting in net-zero carbon emissions.

Meanwhile, researchers are continuing to find other applications for wood, as David N. Bengston noted in The Revolutionary Role of Wood in Our Future.

For example, power generating wood flooring was being tested at the University of Wisconsin-Madison. Made from chemically treated recycled pulp, it can produce an electrostatic charge as people walk across it, capable of powering lights and smart building sensor networks. Another example cited involves a chemical process that removes lignin from natural wood fibres to produce a transparent wood substitute for glass windows.

Additionally, as more manufacturers get involved with mass timber, the price will likely lower and because it lends itself to modular construction, it can be used to construct safe, fire-resistant, and affordable housing on a large scale.

Balancing the environment and the economy

Michael Green has likened the current age “to the beginning of the steel revolution 120 years ago.” While that may be true, and while all the wonderful things we’ve heard about tall wood buildings being tested for fire and seismic safety may also be true — as well as the hope they will help achieve net zero carbon emissions goals — cautionary thoughts remain.

Because of price volatility, inflation, forest fires, woodland pests, supply chain issues, and the dispute over the softwood lumber trade which has been going on between Canada and the U.S. since 1982, mass timber may not be as economical as proponents of its use are hoping. The same issues regarding lumber will also affect mass timber and will need to be solved.

Questions linger about emissions coming from the chemical components of the structural adhesives used in the lamination process. Among them are emulsion polymer isocyanate (EPI), polyurethane (PUR) and Phenolic types which use formaldehyde (PRF), but which is used less often. The Canadian Wood Council offers assurance that all adhesives must comply with health safety codes and have been evaluated for heat performance during exposure to fire. Not so long ago, however, people believed the use of asbestos in wallboard and lead in paint and water pipes was harmless. Should more testing regarding its effects on human health be carried out with regards to off-gassing?

And finally, we need to think about where all this wood that can beautify and reduce GHG emissions in the urban landscape is originating. From forests, obviously, but is there a guarantee it will come from sustainably managed forests which practice selective cutting and other good management practices and not from forestry companies that engage in clear cutting? Are the companies investing in re-forestation programs to replace what is logged? Or, having removed a major source of carbon sequestration, are they then causing further destruction by leaving the land denuded and susceptible to flooding and soil erosion?

Are old growth forests, including those within national parks in both Canada and the U.S., off limits to logging? If they’re not, we’re sacrificing forests which provide habitat for diverse species, protect our water supply, prevent soil erosion, and sequester carbon in order to save our cities.

Said Jonathan Wilkinson, Canada’s Minister of Natural Resources speaking with regards to the Duchesnay Creek Bridge, “There is no solution to climate change that does not involve our forest. Creating new markets for Canadian timber supports our forestry workers, creates jobs, and gets us to net zero. By supporting the use of wood in construction, we are taking action to protect our planet and support our communities.”

Worthy sentiments to be sure. But we wish, in the midst of all the excitement and optimism speaking to the benefits of increasing wood construction through mass timber there was more frequent mention of sourcing wood only from sustainably managed forests which have received certification from such bodies as the Forest Stewardship Council. Certification from this organization “confirms that a forest is being managed in such a way that preserves biological diversity and benefits the lives of local people and workers while ensuring it sustains economic viability.”

For the industry to continue to be viable, it must protect the forests, our national treasure and renewable resource, which make all of these exciting advances in wood construction possible.

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