Mass timber is taking root in commercial construction

By Patrick McBride, Head of Construction Property

As the desire for more sustainable, cost-effective, environmentally friendly building materials becomes an even greater priority in the minds of architects, owners, project managers and general contractors, attention is turning to a bold, innovative material that promises to revolutionize commercial construction.

It’s called wood.

Okay, so humans have been building with wood for thousands of years, from tribal villages to raised ranches on that suburban cul-de-sac. But as society comes to terms with the ultimately unsustainable carbon impacts of large-scale steel and concrete fabrication, a new generation of wood construction materials is changing the game in the execution of commercial projects. Mass timber, a relatively new approach to the fabrication and production of strong, durable and sustainable wood structural members, walls, floors and other components is rapidly becoming the building material of choice for a growing number of bold and ambitious commercial projects in the U.S. and around the world.

As one of the world’s leading construction insurers, Zurich is committed to being a part of the future of the design and construction industry, which is actively exploring and opting for environmentally responsible alternatives to conventional building materials. We stand ready to support this exciting trend with insurance programs offering up to $50 million in capacity to qualified customers who are embracing the potential of mass timber as one of the solutions to the sustainability and environmental challenges facing our world today.

Not your grandfather’s plywood!

Mass timber is a class of engineered building materials fabricated from layers of wood laminated together usually with a strong adhesive under great pressure. At first blush, this may sound a little like plywood, that humble, workhorse material found in sheds and workbenches. But while the principle is similar, comparing mass timber with conventional plywood would be like considering the performance of a 1920’s biplane with a modern jet fighter. Mass timber is a very strong, durable, versatile, and aesthetically pleasing building material that can do just about anything conventional building materials can do, from strength and stability to fire safety.

Mass timber components are manufactured using several processes. Cross-laminated timber (CLT) bonds smaller wood components or dimensional lumber together in layers using a powerful adhesive, with the layers oriented at 90-degree angles for maximum strength. Glue-laminated timber (GLT) framing members are similarly compressed with individual layers aligned in the same direction, again bonded together under high-pressure for strength. Mass timber components may also be manufactured using nails (NLT), and even wooden dowels (DLT) to hold the individual wood layers together to create wall and floor panels used in some applications.

CLT was developed in the early 1990s in Austria and Germany, spreading across Europe in the early 2000s.¹ With the rise of the “green building” movement in Europe, especially for residential construction, the strength, durability, sustainability and aesthetics of mass timber won the material wider and wider acceptance, with it ultimately being incorporated into larger and more ambitious projects.

Such projects are going up and growing taller around the globe. Soaring above a picturesque Norwegian lake 100 kilometers north of Oslo, the 18-story, 280-foot Mjøstårnet Tower became the world's tallest timber building when it opened in 2019.² Nicknamed the “Wood Hotel,” the mass timber building houses apartments and office space. Vancouver, British Columbia, now boasts a 174-foot student residence hall built using mass timber.³ And in Milwaukee, WI, work is progressing on a 238-foot mass timber apartment block scheduled to open in 2022. ⁴ These are just three, current examples, with many more completed, in development and under construction.

While projects like these are examples of the bold thinking driving some applications, commercial projects of medium range and height represent what some view as the “sweet spot” for this evolving construction option, as designers and project owners become more accustomed to the use of mass timber.

Putting it together

Manufactured under controlled conditions, mass timber columns, support beams, wall panels, floors and other components can be protected against the environmental stresses, including water when properly protected, that can affect conventional light-frame construction materials stacked at a jobsite. Upon delivery, mass timber components can be rapidly fitted together and secured, expediting the construction process. Upon completion, designs incorporating mass timber deliver not only great strength and durability, but also an aesthetically pleasing atmosphere and perception of environmental sensibility that a firm’s employees, customers and visitors appreciate.  In essence, mass timber buildings can increase the occupant’s connectivity to the natural environment and improve feelings of well-being. And many owners will appreciate completing a project in less time than might otherwise be required for conventionally framed construction, allowing earlier occupancies.

Because the overall weight of a completed structure built largely or entirely of mass timber will be less than the same project had it been built using steel and concrete, the foundation requirements may be reduced, thereby further reducing the use of concrete and steel in the project. This characteristic also delivers a reduced environmental impact, shortens project schedules and may in turn lower initial costs. A significant, ancillary benefit of mass timber construction is that buildings may be more resilient and perform better against seismic stresses in regions that are seismically active.

Mass timber construction also delivers a significantly reduced environmental footprint than the more carbon-intensive processes involved in the manufacture of steel, concrete and other materials. By one estimate, substituting mass timber for concrete and steel produced with traditional manufacturing processes can reduce carbon emissions from construction by 25-40%.⁵  While concrete and steel production emits large amounts of carbon, trees absorb it throughout their lifetimes, essentially sequestering it. That carbon remains locked in the structure of the building for its entire working lifespan. And with the number of mass timber buildings expected to double every two years through 2034, the building industry has a pathway to storing more carbon than it emits.⁶

What about fire safety?

Standards for the manufacture and use of mass timber in the U.S. are established in the International Building Code (IBC) as developed by the International Code Council (ICC) organization. In the U.S., the relevant ICC codes are now accepted by most states, in some cases with local variations. A 2021 addition to the IBC model building code recognizes three distinct classes for mass timber construction based on building height and floor area. Type IV-C buildings max out at a height of nine stories, Type IV-B structures can rise up to 12 stories, and Type IV-A projects can climb to 18 stories in height.

Each of the three IBC classifications have differing “encapsulation” requirements, meaning the degree to which exposed mass timber supports, panels and flooring must be further protected with the use of drywall, gypsum or other fire-resistant materials. The taller the structure, the more encapsulation required by code, with the shortest Type IV-C structures requiring the least. But while encapsulation provides additional fire protection, mass timber components – especially heavy structural members – are so densely compressed and lacking in interior voids and air pockets that they have been shown in fire demonstration tests to have inherent fire-resistant properties. In controlled tests, external charring acts to further insulate and protect the strength of the mass timber supports, differentiating them from the poorer fire-resistance qualities of traditional light wood frame elements.

Obviously, when visualizing multi-storied structures built largely or completely from wood, some observers unfamiliar with the characteristics of mass timber may immediately raise questions about fire resistance and safety. Those questions are increasingly being answered by ongoing testing by respected fire safety organizations. Among these, tests of both gypsum-encapsulated  and non-encapsulated CLT demonstrated its ability to meet and exceed two- and three-hour fire resistance standards under ASTM International requirements.⁷

Responding to an expanding, global market

Presently, most mass timber components and materials are manufactured in Austria and Canada customized to designers’ and contractors’ specifications in the U.S. and other markets. But with the exploding interest in mass timber construction, new manufacturing facilities are going up around the globe. According to one market research organization studying the mass timber industry, the global market for CLT reached a value of $1.07 billion in 2020, with expected growth of up to 13.2% during the span of time from 2021 to 2026.⁸

In recognition of the rapidly growing U.S. market for mass timber construction, Zurich North America is launching a new Mass Timber Builders Risk proposition, available both as a standalone solution or incorporated as part of a master Builders Risk program. As noted earlier, the new proposition will allow us to deploy up to $50 million in capacity for highly qualified risks.

While we continue our own studies into mass timber, Zurich acknowledges that the product represents an innovative, sophisticated construction technique that has been shown to be structurally sound, sustainable and environmentally conscious. As such, the mass timber market aligns with our own commitment to work with customers and distributors in ways that will help businesses achieve a reduced carbon footprint and a more sustainable future for our communities and our planet.

References

1. “History of CLT.” CLT Panels USA. NC State University 2021.
2. Holland, Oscar. “Has the wooden skyscraper revolution finally arrived?” CNN Style. 19 February 2020.
3. Ibid.
4. Ori, Ryan. “Mass timber construction is becoming more widely used throughout the U.S. When will it arrive at the home of the Great Chicago Fire?” Chicago Tribune. 28 September 2021.
5. “Mass timber: Wood is prominent in construction’s future, value for carbon removal to be determined.” The Economist Intelligence Unit.
6. Caulfield, John. “A new report predicts significant demand growth for mass timber components.” Building Design + Construction. 5 July 2020.
7. “Mass Timber: Performing to the Highest Standards.” American Wood Council.
8. “Cross-Laminated Timber Market: Global Industry Trends, Share, Size, Growth, Opportunity and Forecast 2021-2026.” IMARC.

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