Mention panelized building and most dealers will imagine either structural insulated panels or wall sections pre-framed with conventional lumber and sheathing. But another option just appeared on the horizon: Cross-Laminated Timber (CLT). The product has earned U.S. code approval, and supporters believe that it holds great promise for certain types of commercial and residential structures.
John “Buddy” Showalter, vice president of technology transfer at the American Wood Council, describes CLT as “plywood on steroids.” It’s a solid wood structural panel made from dried dimensional lumber stacked together at right angles in three to seven layers, then bonded under pressure with a thermosetting adhesive. Thicknesses range from 4 to more than 12 inches. Lengths can exceed 40 feet. It’s used to create walls, floors, and roofs, with panels custom-cut for each project. The panels’ hefty weight (from 3,000 to 12,000 pounds each) means that they have to be set with a crane.
There’s a lot to like about CLT. It’s strong and dimensionally stable, weighs less than concrete, and is made from a renewable resource. It’s also naturally fire-resistant. In 2012, FPI Innovations, a forest products research center in Quebec, published the results of eight different tests conforming to the ASTM E119 and Canadian ULC standards for fire resistance. The tests confirmed that CLT chars at a standard rate for mass timbers of just 1.5 inches per hour.
These benefits have made it an attractive option for mid-rise commercial and mixed-use structures worldwide. Signature projects include a 10-story apartment tower in Melbourne, Australia, and a 14-story building scheduled for completion this year in Bergen, Norway.
The product has only recently made its way to the U.S. Kris Spickler, U.S. representative for Structurlam, a British Columbia-based CLT manufacturer, identifies the first U.S. structure project as a 78-foot tall bell tower built in 2010 in Gastonia, N.C., and counts about 15 U.S. projects completed since then. In contrast to the much-publicized multi-story buildings overseas and in Canada, U.S. projects have been less ambitious—at least so far. They include an elementary school in West Virginia, a small retail building in Montana, and private homes in Washington, Oregon, New York, and West Virginia.
Codes Are Catching Up
One reason for the slow pace of adoption has been a lack of code recognition. Structural engineer Darryl Byle served as project manager for the Montana project, a two-story infill structure in downtown Whitefish. He spent three months working with the local code official to get approval as an alternative construction method.
But permitting should get easier. The International Code Council has since approved CLT for inclusion in the 2015 International Building Code’s heavy timber construction classification. And in February the American Wood Council added a CLT design chapter to its National Design Specification. It includes design data for members and connections.
CLT supporters see code inclusion as an important step to a wider market. Byle is so optimistic about the material’s future as a building system that he’s formed a company, Cross Lam Timber Solutions, in Kalispell, Mont., to help architects and contractors nationwide design and build with it. “In the past year I have worked on well over $20 million worth of projects, up from $5 million the year before,” he says. These include custom-designed homes on Long Island and New Jersey, the latter of which is a Passivhaus project.
Byle says that CLT is perfect for energy-efficient buildings. The solid panels simplify the process of making an airtight building envelope, and the fact that they’re insulated on the outside eliminates thermal breaks. Solid wood walls also provide what he calls hygro-thermal mass: the ability to absorb and re-emit moisture as well as heat, thus moderating fluctuations in both.
Builders who have used CLT comment on how quickly structures go together. Sloan Ritchie, owner of Cascade Built in Seattle, recently framed a complex architect-designed CLT home on an in-town lot and says that the panels knocked a month or two off of construction time compared to standard framing.
Getting those time savings requires good management systems. Charles Judd was the owner of Blue Heron Timber Works in 2014, when the company built a 40,000-square-foot school in Franklin, W. Va. He says that implementing the material requires careful organization between the builder and the supplier. “The panels have to be delivered so they can be stacked in the order and orientation they will be used,” he says. “They also have to be stored on a very flat surface so they don’t warp.”
While the material offers cost savings over steel and concrete, the cost of CLT is about twice that of standard wood framing. Some, including Spickler, believe that this will severely limit CLT’s potential to compete with conventional light framing.
Byle points out that the high cost is thanks in part to the need to ship massive panels over long distances from plants in Canada or Europe. “Shipping can account for 20% to 30% of the cost,” he says. Even if costs come down, he doesn’t see production home builders using CLT, although he believes that plants strategically located around the U.S. could lower costs enough to capture a 5% share of the combined commercial and custom residential market.
What would this mean for pro dealers? Spickler frequently gets calls from lumberyards with that question. The short answer is that he believes it will remain a special-order item for the foreseeable future. It’s conceivable that a dealer could stock large panels and custom-cut them as needed for local customers, but it would take a major investment in equipment. “I’ve seen a little of that in Europe,” he says, “but their market has had 20 years to develop.”