By Dr. Richard Vlosky and Mason T. LeBlanc
Mass timber has been produced and used in many forms over the past decade. Examples are glulam beams, laminated veneer lumber and parallel strand lumber. More recently, new entrants have been developed and are being adopted into the North American engineered wood product building materials family of products. Newer structural panel products, such as nail-laminated timber, dowel-laminated timber, mass plywood panels and cross-laminated timber, have experienced years of product testing and manufacturing learning curves with increasing production.
Cross-laminated timber is a large-scale, prefabricated, solid engineered wood panel. Lightweight yet very strong and with superior acoustic, fire, seismic and thermal performance, cross-laminated timber is also fast and easy to install. It also generates almost no waste onsite. Cross-laminated timber offers design flexibility and few environmental impacts. For these reasons, cross-laminated timber is proving to be a highly advantageous alternative to conventional materials, like concrete, masonry or steel, especially in multifamily and commercial construction.
A cross-laminated timber panel consists of several layers of kiln-dried dimension lumber stacked in alternating directions, bonded with structural adhesives, and pressed to form a solid, straight, rectangular panel. Cross-laminated timber panels consist of an odd number of layers (usually three to seven layers) and may be sanded or prefinished before shipping. While at the mill, cross-laminated timber panels are cut to size, including door and window openings, with state-of-the art computer numerical controlled routers capable of making complex cuts with high precision. Finished cross-laminated timber panels are exceptionally stiff, strong and stable, handling load transfer on all sides.
Cross-laminated timber manufacturing and use in multistory buildings and other structures is a well-established and fast-growing industry in Europe, but adoption of this building technology has just begun to emerge in the U.S. and Canada. In 2017 and early 2018, 13 new mills were proposed, including new mills in the U.S. and New Zealand. Of those, seven are under construction and will be online by 2020. In 2016, the global output of cross-laminated timber was estimated to be 1 million cubic meters and is forecast to reach 3 million cubic meters by 2025.
Because of its 20-year history in Europe, there are abundant examples of the potential for building with cross-laminated timber. In Europe there are currently more than 600 cross-laminated timber structures and dozens of manufacturing facilities. In Europe there have been 18 all-timber buildings of seven to 14 stories built, with nine buildings using timber and conventional materials from seven to 20 stories. There have also been nine proposed buildings from eight to 35 stories. Most of these buildings are in the United Kingdom and France. The North American market alone is said to have the potential of 2 to 6 million cubic meters.
The U.S. cross-laminated timber industry started in Oregon and Washington using Douglas-fir dimension lumber as raw material. Both states recently approved statewide building codes that include tall timber buildings. Cross-laminated timber manufactured in North America must meet stringent product standards and be certified to the standard for performance-rated cross-laminated timber set by APA – The Engineered Wood Association, the ANSI/APA PRG 320-2012 sandard. Cross-laminated timber manufactured outside of North America may not meet these performance standards for wood construction.
The potential markets for cross-laminated timber in the U.S. are enormous if architects, builders, contractors, engineers and building owners accept the product as a substitute for steel and concrete construction. Recent studies about properties of southern yellow pine cross-laminated timber have proven to surpass standards, but knowledge of the material in the South is still low. The southern U.S. has ample southern yellow pine resources to meet the potential market for cross-laminated timber, as there are many sawmills in the region that have significantly increased production. Overall, research, development and successful examples will continue to convince stakeholders and influencers as well as the public of the soundness and the possibilities of using cross-laminated timber in the U.S. and, particularly, in the South.
— Richard Vlosky, Ph.D., is the director of the Louisiana Forest Products Development Center and the Crosby Land and Resources Endowed Professor of Forest Sector Business Development in the School of Renewable Natural Resources at the LSU AgCenter. Mason T. LeBlanc, M.S., is a procurement analyst for Drax Biomass in Monroe, Louisiana.
Photo info: Cross-laminated timber construction.