The market for CLT panels in the US is expected to reach over two million m3 in the next ten years. The current manufacturing capacity in the US is less than 200,000 m3, which represents an excellent opportunity for the hardwood industry.
Architects in North America and Western Europe are particularly interested in hardwood CLT panels because hardwood lumber is more aesthetically pleasing than softwood lumber. Plus, CLT panels made out of certain hardwood species could be lighter and occupy less volume than softwood CLT panels because of the superior mechanical performance of hardwood species.
Unfortunately, hardwood lumber cannot be used in structural CLT panels because the North American CLT standard APA/PRG 320 does not allow it. However, a CLT mill interested in manufacturing and selling hardwood CLT panels for structural use could pursue a custom certification by a third party to make hardwood CLT panels available to the construction market.
At Virginia Tech (VT), we continue to conduct research to overcome barriers preventing hardwood species from accessing this market opportunity. Our work has focused on the potential to use yellow poplar lumber as raw material for structural CLT panels. West Virginia University is also researching yellow poplar CLT panels to pursue the inclusion of yellow poplar CLT panels in the CLT standard.
In 2012, Dr. Daniel Hindman, a wood mechanics professor at Virginia Tech, was awarded the first-ever hardwood CLT research grant to determine the potential use of yellow poplar in structural CLT panels. Results of this grant indicated that strength and stiffness of yellow poplar CLT panels were superior to similar CLT configurations made with southern yellow pine. This project had West Virginia University and the University of Tennessee as partners.
In 2016, Dr. Henry Quesada and Dr. Brian Bond (also from Virginia Tech) were awarded a second grant to investigate the potential of hardwood sawmills to produce hardwood lumber for structural CLT panels. An economic model is being developed to determine the best product mix of manufacturing appearance lumber and structural lumber. Preliminary results indicate that for species such as yellow poplar, hardwood mills could produce appearance lumber from 1 common and higher grades and structural lumber from 2 common and lower grades without impacting revenue. This grant is also surveying the willingness of US hardwood sawmills to produce structural lumber from hardwood species. Two of the main adjustments that hardwood sawmills would have to address are: implementing structural grading and producing fixed widths.
Architects Kay Edge and Edward Becker, along with students from the School of Architecture at Virginia Tech designed and built a train viewing platform made of yellow poplar CLT panels in 2018. The structure is a proof-of-concept and is the first structural application of hardwood CLT panels in the US. The data generated by Hindman’s 2012 hardwood CLT project was used to obtain the construction permits. See Figure 1. The project is located in Radford, VA.
In this new project, Virginia Tech will work with Smartlam in Montana to produce CLT panels made of yellow poplar. APA will test the panels. Hardwood organizations such as the Appalachian Hardwood Manufacturers, the National Hardwood Lumber Association, and the Hardwood Manufacturers Association are partnering with Virginia Tech to promote the project among their members and find potential donors of yellow poplar lumber for the manufacturing and testing of the CLT panels.
Another barrier that this new project is trying to address is structural grading for hardwood lumber. Rules to structurally grade hardwood lumber have been developed, but hardwood sawmills do not use them, mostly because there is no market for structural hardwood lumber. This new grant will work with NELMA, a grading agency, to train interested hardwood sawmills on how to apply structural grades for hardwood lumber.
Other factors that might impact the use of hardwood lumber for structural CLT panels are:
- Prices: Prices of #1 and #2 softwood lumber are usually less than $450 per thousand board feet. However, species such as yellow poplar and soft maple might have a chance to compete in terms of prices.
- Volume: A medium-size CLT mill will produce around 50,000 m3 or 21.2 million board feet per year. An average hardwood sawmill produces less than 20 million board feet per year. Several hardwood sawmills would work together to supply lumber to such a CLT mill.
- Adhesion: Chemical companies have been able to produce glues that work very well with softwood species such as spruce, Douglas fir, and southern yellow pine. The same adhesives have been used with yellow poplar with mixed results. This could be an indication that a specific formulation for gluing yellow poplar needs to be developed.
If you have any questions about the hardwood CLT projects at Virginia Tech, please contact Dr. Henry Quesada at [email protected]
Acknowledgment: This work is funded by the US Forest Service through grants 19-DG-11083150-021 and 16-DG-11083150-053.