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Tim-ber! Builders Herald the Coming Wave of Mass-Timber Construction

mass timber construction composite

In the Wild West that is the construction industry, there’s a new sheriff in town: mass timber. “Within five years, or a little less, the question ‘should this be a mass-timber project?’ will be confronting most commercial projects,” says Andrew Tsay Jacobs, director of the Building Technology Lab at Perkins+Will in Los Angeles.

Mass timber” refers to composite-wood systems that combine multiple pieces of wood into larger structural elements whose strength often rivals that of concrete and steel structures. The wood elements are also a renewable resource that sequester carbon. Largely popularized in Europe for its enhanced building performance and sustainable attributes, mass timber is steadily creeping into more and more high-profile North American projects.

mass timber construction
Mass timber often rivals steel and concrete in strength. 

New Codes, New Opportunities: Are Builders Ready?

At the end of 2018, the International Code Council (ICC) approved new guidelines that will allow builders to create mass-timber structures as tall as 18 stories once the changes are ratified in 2021. The building code is changing “in a way that it hasn’t in 100 years,” Tsay Jacobs says. “It’s probably the largest, most impactful code change in our lifetimes.”

For risk-averse builders, however, adapting to mass timber means embracing big changes. Firms aren’t yet equipped with resources like relevant cost-estimation tools and can feel constrained when it comes to finding the headroom to innovate. Additionally, working with prefabrication subcontractors adds legal and contractual burdens and can potentially undercut a contractor’s own labor force. But, says Tsay Jacobs, “One experience with mass timber is usually all it takes for a contractor to begin to sing its praises. The ease of construction in preplanned projects is a huge benefit to general contractors, and the speed of construction is a huge benefit to developers.”

mass timber construction
New codes will allow mass-timber buildings as high as 18 stories. 

Perkins+Will is exploring ways to reconcile these new approaches in design and fabrication at the Autodesk Technology Center in Boston. There, the firm conducted research investigating how the industrialization and automation of mass timber will change the industry. Its experiment included using an automated robot arm to build a wood pavilion out of nail-laminated timber (NLT). In partnership with developers and contractors, Perkins+Will’s goal is to develop mass-timber solutions that integrate the design-to-fabricate-to-build process and make it as parametric and seamless as possible.

This structural medium will create new typologies for builders, giving them guidance for evolving their practices in a world where mass timber is omnipresent. That means builders need to take ownership of this transition. “If you don’t address how that code change will affect your business, other developers, contractors, and fabricators will, and they’ll solve the questions that mass timber asks,” Tsay Jacobs says. “They’ll take hold of the opportunities that mass timber gives over steel and concrete, and you’ll be left scrambling.”

Shifting Processes to Planning Phases

In large part, building with mass timber requires adopting modular and prefab construction methods, shifting resources and labor from the jobsite to the factory floor and the preconstruction and planning phase. “It’s a clean jobsite,” Tsay Jacobs says. “It’s a jobsite that comes together like LEGOs. The pieces have to fit and have to be planned correctly.” Mass-timber structures can be built 10–30% faster than standard construction, and because the process requires little skilled labor, builders have new flexibility in crew sizes.

The builder and developer LendLease, for example, has constructed a series of military hotels with veteran labor. “On-site, it’s as straightforward as you would imagine,” says LendLease’s resident mass-timber expert, Lisa Podesto. “A lot of people think there’s a catch. Connections are simple and it goes up really fast. What’s the catch? The catch is that it takes a lot of collaborative work before you get to the site.”

Given the recent emergence of mass timber in North America, building successfully with it requires more up-front study, communication, and time investment all around. “Traditional design-bid-build processes won’t work with mass timber,” Tsay Jacobs says, “because they don’t allow for comprehensive planning between designers and builders using a medium where well-established standards don’t exist yet.”

Mass-timber systems are not just acting as structures; they often contribute to fire, aesthetics, acoustics, and building envelope, and because the elements are prefabricated, the design has to account for these aspects as well as penetrations with a high degree of accuracy.

If designed in isolation without fabricators and trade partners, a mass-timber project will likely run into dimension discrepancies and material-sourcing issues. Mass timber is much better suited to design-build arrangements where contractors work closely with designers from the project’s inception. “Mass timber gives everyone the opportunity to come to the table earlier and develop seamless design-to-construct workflows,” Tsay Jacobs says.

The current focus is on tall mass-timber structures, but the material can adapt to most places and project types. One entry-level way for builders to get started with mass timber is to use it as a roof deck. (Perkins+Will has used mass-timber roofs on train station projects in Vancouver and Montreal.)

mass timber construction brentwood skytrain burnaby
Perkins+Will used mass timber to create the roof of the Brentwood SkyTrain station in Burnaby, British Columbia. Courtesy Perkins+Will.

Buildings with large footprints work well with cross-laminated timber (CLT) panel systems, which involve gluing segments of wood at perpendicular angles for added strength. The panels “take 5 to 20 minutes to install, and then you’ve suddenly got upward of 200 square feet of floor/roof deck completed, as far as structure goes,” Tsay Jacobs says.

Podesto says the most practical mass-timber building types from a cost perspective are commercial office spaces. “This is where you see developers and design teams most successful in applying mass timber in a cost-competitive way,” she says. “Most commercial office spaces are fairly standard post-and-beam steel systems; shifting these simple, repetitive structures to mass timber offers both a more distinctive product for the same price or less.”

If You Build It, They Will Come

Like the design teams who are trying to figure out how to most efficiently use these new systems, the US supply chain is also working on refining efficiencies, creating new secondary processing industries and building in-house modeling and fabrication expertise while also working on plant and process efficiencies.

As more mass-timber fabricators come online and manufacturers refine their processes, services, and material offerings (the first plant east of the Rockies just opened up in Alabama), prices are likely to come down and product diversity will go up. Within five years of the code change, Tsay Jacobs says, you can expect to see an explosion of mid-rise mass-timber construction. “This is not a matter of ‘if,’” adds Podesto. “It’s a matter of ‘when.’”