If Yugon Kim realizes his dream, the new office building or housing complex going up in your city may be made out of large hardwood panels called cross laminated timber (CLT). The technology behind CLT has been used for decades in Europe, and it is just beginning to take root in the United States with softwood CLT leading the way. Kim’s Boston-based, architectural design firm IKD just won a $250,000 grant from the Forest Service for designing, developing and constructing the first hardwood CLT demonstration project in the United States.
The aim is to take low-value hardwoods and turn them into a high-value CLT construction project as a proof of concept. Kim explained, “Over 50% of every hardwood log in the region goes to low-value materials like pallets and cants. Our idea is to utilize this material and to upcycle it.”
Kim along with his design partner Tomomi Itakura have created an outdoor CLT construction project that is titled the Conversation Plinth and will be integrated as circular discs that provide a platform for viewing a sculpture at the Cleo Rogers Memorial Library.
Kim suggested, “The ultimate goal is to construct buildings in the United States using hardwood CLT. Our research hopes to lead toward hardwood mass timbers being used for U.S construction projects.”
The Conversation Plinth was designed for Exhibit Columbus, the annual celebration of architecture, art, design and community in Columbus, Indiana. IKD’s design was selected to win am inaugural J. Irwin and Xenia S. Miller Prize as part of a national competition.
The simple reason is that Kim wanted to use local materials, and hardwood is in abundance in Indiana. Also, he saw opportunities due to the availability and density of low-grade hardwoods. Most of the CLT projects in the United States have utilized softwood and have taken place in the West. Only two companies currently are certified to make CLT in the country, DR Johnson and SMARTLAM. And hardwoods are a novelty that shows promise.
Kim commented, “Some of the benefit of hardwood CLT over softwood is that hardwoods have superior structural capacity and mechanical properties.”
Hardwood is denser than most softwood. And it might be able to have less volume and still have same structural capacity of softwood or can achieve larger spans or clear vertical spans with same dimensional thickness. Also, from an aesthetic standpoint, hardwoods can look better than softwoods. Just think about how hardwood floors have become the rage due to their beauty and durability.
The project is using mixed species of hardwoods including beach, ash, oak, hickory and maple as well as hybrid panels that utilize both hardwood and softwood. These species have similar structural capabilities and work well together. Kim added, “Our idea is to use a mixed species to try to utilize as much of the grade three common pallet lumber as possible to diversify the low-grade hardwood market.”
Since this is the first commercial project using hardwood CLT in the United States, there have been some learning curves. Kim explained, “The biggest issue we are running into is glue adhesion. But we are working through that and have found solutions.”
Kim and his team is working with SMARTLAM and mass timber engineer Chris Carbone from Bensonwood to formulate the CLT panels used to produce the Conversation Plinth. SMARTLAM is doing structural tests as the products are developed.
CLT is not traditionally used outside, but this is a temporary structure. And they are putting a finished sealer on top to prevent water penetration within the panel assembly.
The Conversation Plinth will be up for three months in Columbus, and the unveiling is scheduled for August 26th.
Potential Industry Impact?
The hardwood CLT project is intended to demonstrate the efficacy of the material and lead the way to more construction projects using low-grade hardwoods for CLT.
Kim explained, “There are a lot of unknowns when working with hardwood CLT. There are glue adhesion issues, sourcing, etc.” Kim’s project helped to flush out those issues and look for solutions as well as develop models that can be used for future commercialization.
Not only is this the first ever domestic use of hardwood CLT with low-grade lumber, it is also the first commercial pressing of hardwood CLT and hybrid hardwood/softwood CLT.
Because grade three common is random width material and not kiln dried, it had to go through a number of processes before being used to produce CLT. For starters, the wood needs standardized moisture content in the range of 8-12%, which is much lower than even what is achieved through standard kiln drying. All four sides had to be planed to achieve the right dimensions.
Kim said, “Additional processing makes a lower-value material more expensive, but in the long run the margins of hardwood CLT may make it still come out on top.”
Kim even suggested that hardwoods in the future might achieve a premium price compared to softwoods due to the strength and appearance qualities of the material.
CLT is far from becoming a common thing. But it shows significant promise and is attracting more attention each day. Eventually CLT might become a major competitor for raw materials to the wood packaging sector. Due to the large pieces needed to create CLT panels it is doubtful that waste wood or scraps could ever be used in the process.
CLT is made from long pieces of lumber glued together and then layered perpendicularly to form thick panels which can be as large as 10’ wide and 40’ long. It is likely that many mills would be required to feed even one CLT production facility.
Kim’s is working closely with Koetter Woodworking in Borden, Indiana, developing process that involves sourcing from multiple sawmills, cutting the material, and further prepping it with the final panel assembly and construction taking place at SMARTLAM’s facility in Montana.
Transportation costs were a major factor for this project because of the limited number of certified CLT plants. Kim added, “There is a race to develop CLT operations across the United States because transport is a large part of the cost for this project. If we can have a plant in the region, that would be the ultimate next step to improve the marketability of the product.”
When the project is completed, it will be on display and will then be evaluated for performance. Kim said that his firm is going to continue to work with SMARTLAM, Koetter Woodworking, Bensonwood, Clemson University, the Indiana Hardwood Lumber Association and the National Hardwood Lumber Association to develop a panel that can be certified by the American Plywood Association. They will tweak panel assembly process to get all certifications in place. Also, facilities need to spring up in the hardwood area to make CLT panels.
There are still some major hurdles standing in the way from major market acceptance. Some people still think that wood has major issues including structural stability, durability and combustibility. But Kim said if people understand what CLT is, they will come to realize that CLT exceeds their concerns.
Kim added, “Another major hurdle is that CLT is a new building material so a lot of contractors are unfamiliar with how to use it… CLT is a new tool in the construction tool box.”
Having worked with wood for years in sculpting and furniture design, Kim knows the value and benefits of wood. That is one of the reasons he believes so much in the future potential for CLT.
Kim pointed to construction projects in the United Kingdom that have proven hardwood CLT can lead to construction projects that can be done cheaper and faster than traditional methods, such as steel and concrete. CLT can provide a higher use of low-grade lumber. Made in America, CLT can provide rural jobs using a local, renewable resource. “Hardwood CLT checks all the boxes. There are a lot of reasons why the sky is the limit for this approach to construction.”
Kim forecasted, “We are on the cusp of a new way of doing buildings in this country. It is an exciting time to be involved in wood construction. America used to be built with timber and then it stopped for a number of reasons. Once again, I can see a future where timber buildings are part of our urban landscape.”
For more information, visit www.i-k-design.com or https://exhibitcolumbus.org/exhibition/conversation-plinth.