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Mass timber continues to be a growing trend for buildings in Oregon as teams seek faster, more sustainable projects with less environmental impact.

Wood requires the least amount of energy to produce in comparison to other building materials such as steel and concrete; it鈥檚 also renewable and sequesters carbon. The carbon dioxide in the air is extracted and carbon is transformed and stored in the wood fiber, taking a greenhouse gas out of the atmosphere, Western Wood Structures mass timber sales specialist Wilson Antoniuk said.

Engineered wood products include cross-laminated timber (CLT), laminated veneer lumber, glue-laminated lumber (glulam), dowel-laminated timber (DLT) and nail-laminated timber (NLT).

Laminated veneer lumber

Freres Engineered Wood鈥檚 mass ply products include patented, veneer-based, CLT-certified Mass Ply Panels (MPP) and Mass Ply Lam (MPL) beams and columns. The company began producing veneer in the 1950s, adding plywood in the 鈥�90s and then developing MPP in 2017. Mass ply is a mass-timber panel assembled by combining thin layers of stress-rated Douglas fir veneer, in the long and cross direction, creating a large-format wood platform that is then prefabricated to exact dimensions with a computer numerical control (CNC) machine.

Freres Engineered Wood鈥檚 products are under the same code as cross-laminated timber but are veneer-based rather than lumber-based, said Tyler Freres, vice president of sales for the company. The veneer is a Douglas fir panel that is cross laminated but on a thinner cross-section of material.

Mass-timber products manufactured by Freres Engineered Wood often end up in commercial or multifamily buildings; many are multiple stories, including the NHERI TallWood structure. Freres also provided nearly 9 acres of mass timber for the new main terminal roof at Portland International Airport.

Cross-laminated timber and glulam

Glulam was first used in Europe in the 1890s. One of the first glulam structures in the U.S. was a research laboratory at the USDA Forest Products Laboratory in Wisconsin in 1934. Glulam is used for arches, columns and beams.

In North America, CLT is relatively new; it was introduced in Canada in 2011 and the U.S. in 2012, Antoniuk said. But the building material originated in Austria and Germany in the early 1990s, he said.

CLT is made with layers of two-by material and oriented 90 degrees from each layer. It can be used for floors, roofs, and walls.

鈥淲hen they cross laminate the timber, it basically adds dimensional stability, so the panel doesn鈥檛 shrink significantly in any one direction and create noticeable gaps between members,鈥� Antoniuk said.

For glulam timbers, all the laminations are in the same direction, so there will be some shrinkage. There is a necessary gap in between the panels to account for the shrinkage, whereas there is no gap with CLT.

Currently, building codes in Oregon and Washington allow CLT buildings up to 18 stories, with stakeholders expecting that number to increase. CLT has become a popular alternative to traditional materials such as steel and concrete, though Antoniuk said there is usually still concrete or steel in a building鈥檚 core, such as stairs.

Notable CLT projects include the Shiley-Marcos Center for Design & Innovation at the University of Portland; Marshall Elementary School and McLoughlin Middle School, both in Vancouver, Washington; and the pedestrian bridge at Lewis & Clark College.

Glulam projects include the Historic Carousel & Museum in Albany, the Beacon Hill branch of Seattle Public Library, and Concourse D at Seattle-Tacoma International Airport.

Dowel-laminated timber

StructureCraft鈥檚 dowel-laminated timber is an all-wood product that can be used for floors, walls, and roofs. It was invented in Switzerland in the 1990s. DLT 鈥� or DowelLam 鈥� is less expensive to produce than other glue products like CLT, according to StructureCraft. It is common in Europe and becoming popular in the U.S.

To form DLT members, softwood lumber panels are stacked like NLT and friction-fit together with hardwood dowels.

The first project to use DLT in North America was the Museum of Fine Arts, Houston. The mass-timber structure includes DLT roof panels on a glulam post and beam substructure. The project was completed in 2017.

Previous projects that have used DLT include Lakeridge Middle School in Lake Oswego (completed in 2021), the Idaho Central Credit Union Arena in Moscow, Idaho (completed in 2021), and StructureCraft鈥檚 headquarters in Abbotsford, British Columbia (completed in 2022).

Building connections

With any mass-timber project, there is more planning at the front end of development. A building is designed and premanufactured off-site. The structure rises quicker with the prefabricated materials than it would with traditional construction on-site. Not much cutting or drilling takes place on-site, Freres said, but construction is primarily connection of panels and installation of beams and columns. Construction on-site happens very quickly.

鈥淭rade partnering鈥� is an important component of mass-timber projects, since a lot of planning is necessary up front, Antoniuk said. Builders need to involve an experienced mass-timber subcontractor team聽early in the process, typically at the schematic design or design development phase.

Mass timber has its place, Antoniuk said, such as for projects that traditionally featured concrete and steel. These may include office buildings, multifamily buildings, schools, or university buildings. Mass timber does not make sense, however, in standard homes because the price point is not attainable for most people, he said.

鈥淭he mass-timber products all provide fire resistance due to the thickness of the members; one hour of fire resistance rating can be achieved per 1.8 inches of wood thickness,鈥� Antoniuk said. 鈥淭here鈥檚 just different ways to connect it.鈥�

Options include glue, nails, and wood dowels.