Atlantic Forestry July 2020

Mass timber renaissance

I recall having a bit of a eureka moment years ago when I visited the Advanced Engineered Wood Composites Center at the University of Maine campus in Orono. (For anyone who catalogues their old magazines, see “Taking a strand” in the Sept. 2007 issue of AFR. Since then, the facility has been renamed the Advanced Structures and Composites Center, to reflect an expanded mandate.) 

Not knowing much about engineered wood products, and having an aesthetic preference for solid wood, I had always thought of composites as “pressed junk” – just a bunch of sawdust and resin glommed together, offering no positive attributes other than economy. Talking to Dr. Habib Dagher, the lab’s founding director, and Russell Edgar, the composites manager, I got a fuller picture of this sector, and I came to understand a fundamental concept behind cutting wood into a bunch of little pieces and then gluing them together: it’s all about achieving greater and more predictable strength characteristics through the randomization of defects. Such an elegant principle! (It occurred to me this could apply not only to structural materials, but also to economic and political structures in our society – but let’s put that aside for now.)

More recently, I learned about the increasing popularity of nail-laminated timber (NLT), an engineered wood product that has been around for a long time. The new East Hants Aquatic Centre in Elmsdale, N.S., incorporated a bunch of NLT panels manufactured in a temporary shop that was set up in a warehouse at nearby Elmsdale Lumber, utilizing about 85,000 board feet of 12-foot two-by-fours supplied by the mill. (See “Spiked together,” in AFR Jan. 2019.) This product is so low-tech, maybe I could put the kids to work making panels. I keep looking up at the kitchen ceiling, thinking that if I were building a new house, perhaps there’s no need for those big floor joists (and those big cavities that currently serve as mouse habitat), if a stack of two-by-fours would do the trick.

I have learned a lot more from reading the 2020 North American Mass Timber State of the Industry report, which was released in June. The report was developed in conjunction with the International Mass Timber Conference that has been held annually in Portland, Oregon, since 2016. The 2020 edition was cancelled due to COVID-19, but registration is already open for the 2021 conference, running March 30 to April 1. 

The sector has gained a lot of momentum. A key premise of this new report is a projection known as the Marshall Effect (named after Steve Marshall, who recently retired from a 42-year career with the U.S. Forest Service, where he worked to establish the Wood Innovations Program): “Between 2020 and 2034, the number of mass timber buildings constructed globally will double every two years. The result is that the North American building construction sector will reach carbon neutrality.”

A number of engineered wood products are well established in the construction industry – such as plywood, OSB (oriented strand board), laminated veneer lumber, and wooden I-joists. But mass timber panels, which constitute a separate category, hold tremendous potential for replacing steel and concrete in multi-storey buildings – and this is how the major carbon advantages can be achieved. 

NLT is the most rudimentary type, and it is fine for some applications. One variation is dowel-laminated timber (DLT), which involves making panels by drilling holes in the lumber and inserting low-moisture hardwood dowels. The dowels absorb moisture from the surrounding softwood, and expand to create a tight “friction fit” – with no adhesives, and no nails to impinge on the use of CNC tools to cut door and window openings and channels for plumbing, electrical, and HVAC.

However, the leading product appears to be cross-laminated timber (CLT), which comprises alternating layers of lumber oriented perpendicularly, laminated with an adhesive.

Used in floors, interior and exterior walls, and roofs, CLT panels are typically between eight and 12 feet wide, and 3.5 to nine inches thick. “Panel length is limited only by press size and highway trucking regulations,” says the report.

On average, 0.9 cubic feet of mass timber is required per square foot of new construction. The report highlights the fact that a cubic foot of CLT typically requires 20-25 nominal board feet of dimensional lumber – due to surfacing and defect trimming of lumber feedstock. That lost volume is not “waste” – since there are commercial uses for the resulting chips and shavings and sawdust – but it reduces revenue.

For CLT manufacturers, lumber represents at least 50 percent of production cost, and lumber price volatility is a major economic risk. An obvious remedy would be to form partnerships with the sawmill sector. The most common feedstock for CLT is #2 grade two-by-eight-inch softwood lumber, and it must be dried to about 12 percent moisture, instead of the 19 percent deemed acceptable for stick construction. The report notes that the lumber has to be surfaced within 48 hours prior to layup, to ensure good glue bonding, so instead of purchasing dressed lumber and resurfacing it (resulting in reduced volume), CLT manufacturers may prefer to buy rough lumber that has been dried. Another potential efficiency could be achieved by supplying lumber in true random lengths instead of the standard two-foot increments, which would improve yield at the sawmill end. Because the pieces are going to be trimmed and finger-jointed in the CLT plant, length is of no consequence.

ATTRIBUTES

It is well established that people like the appearance of wood buildings, and it has even been shown that wood interiors provide psychological advantages for the occupants. The report summarizes how mass timber has also passed muster in terms of fire resistance, moisture mitigation, acoustics, thermal properties, seismic performance, and resilience to “ballistic situations” (which is a bit chilling). The authors also outline how mass timber fits into the green building movement, providing explanations of lifecycle assessments, environmental product declarations (EPDs), and the complex arithmetic of carbon accounting.

One challenge is a shortage of trained builders. On the other hand, compared to conventional steel and concrete construction, mass timber requires considerably fewer workers at the building site. The labour requirement is partly shifted to the manufacturing plant, which offers advantages in terms of training, safety, comfort and ergonomics, commuting, and opportunities for employees who have less physical strength or mobility. The assembly of components at the building site is considerably faster than steel and concrete construction, but it hinges on intricately choreographed logistics, with materials arriving just in time, in the proper sequence.

Another challenge for the industry stems from public concern about sustainable wood supply. North American demand for mass timber in 2019 is estimated at 20-25 million cubic feet, which equates to 450-500 million board feet of softwood lumber. That sounds like a lot, but it is less than one percent of North American lumber production. The report notes that even if there were a six-fold increase in this sector, consuming three billion board feet of lumber per year, this would be just five percent of current lumber production. Based on North American timber growth rates, that increase in demand is deemed to be well within the bounds of sustainability. Sawmill capacity is also expected to increase accordingly, notably in the U.S. South.

The report includes an overview of current mass timber manufacturers in North America, acknowledging the fact that Canada was out in front – with Nordic Structures launching in Montreal in 2007, followed by Structurlam in Penticton, B.C., in 2010. “Both companies are leaders in architectural and industrial-grade CLT for building purposes,” says the report. More recent Canadian entries include Element5, with facilities in Ripton, Quebec, and St. Thomas, Ontario; Kalesnikoff, in South Slocan, B.C.; and Leaf Engineered Wood Products, in Devlin, Ontario (about halfway between Thunder Bay and Winnipeg).

One of the key messages is that mass timber is not a commodity product like lumber. “Manufacturers tend to work closely with architects and engineers during building design and specification regarding MTP product specifications (size, thickness, strength),” reads the report. “As many in the industry have noted, early collaboration between developers, specifiers, and panel manufacturers is essential for efficient and cost-effective design and construction.”

The report goes into some detail about the types of planning processes and services required. The point is, we’re not just talking about new technology here – we’re talking about new business models. In Europe, the industry has matured to the point that there has been some standardization of panel sizes and engineering characteristics, which has simplified project planning somewhat, but the report predicts that it will be a decade before this occurs in the North American market. As for adopting appropriate technology, North American industry players have learned lessons from the European experience, so they are not starting from scratch – but they are finding that some manufacturers of CLT equipment (the report cites Minda, Ledinek, USNR, and Kallesoe) are currently backordered by 12 months.

When I read about housing starts, which are such an important driver for lumber demand, I sometimes feel discouraged about the type of housing commonly being built. Too often, we are still fostering suburban sprawl – old-fashioned, single-family homes with wasteful driveways and lawns, gobbling up forests or farmland. When I have visited cities where people appear to have a good quality of life, a common feature is mid-rise, high-density housing – with commercial units at ground level, abundant space for pedestrians, and street trees for shade. If mass timber could play a lead role in making this the dominant model for new housing, it would burnish the industry’s green credentials. DL