Cross laminated timber (CLT) has proven to be an amazing alternative to traditional building materials such as steel, concrete, and masonry.
The sustainable construction market continues to grow, and for the foreseeable future, is not showing signs of slowing down. Widespread adoption of greener building practices means sustainability is more mainstream and less of a cost concern.
This leaves room for many customers to seek out assurances that the products they choose for a more sustainable building are not green in name only. They also presume that sustainable designs of the future will require futuristic materials.
Meeting the growing demand for sustainable innovations may be found in a return to our construction roots.
A product known as cross laminated timber (CLT) has been used in Europe for a couple decades now, and has proven to be a startlingly green alternative to traditional “industrial age” building materials.
This engineered wood building system is made from several layers of dimensional lumber boards, stacked crosswise and bonded together, providing dimensional stability, strength and rigidity. The process, deceptively simple, is an elegant one that delivers both in form and function.
Typical structural building components like masonry, concrete, and steel have large carbon footprints.
Weighted with data from the U.S. Green Building Council that 40 percent of national CO2 emissions come from buildings, it is more than clear that meaningful progress can be made in developing sustainable building materials and processes. While many sustainable construction developments rely on intensive manufacturing, CLT helps forge a closer connection between the built world and the natural world.
Cross laminated timber’s features read a lot like the benefits touted by industrial-age products:
With proper design and maintenance, wood structures can provide long and useful service lives equivalent to other building materials. The key is careful planning and understanding of environmental loads and other external factors likely to impact a building over its lifetime.
Strength and Stability
Cross-lamination provides for superior dimensional stability and offers significant shear strength performance at a very unique weight to strength ratio compared to other common structural materials. CLT panels outperform anything currently available in the U.S.
CLT panels can create an effective lateral load resisting system. Researchers have conducted extensive seismic testing on cross laminated timber and found they perform exceptionally well with no residual deformation, particularly in multi-story applications.
Cross laminated timber panels are better insulators, requiring little or no insulation.
Since CLT panels can be manufactured using CNC—computer numerical control—equipment to precise tolerances, the tighter-fitting panel joints results in better energy efficiency for the structure. The solid panels also mean nearly zero air infiltration into the building envelope.
Interior temperatures of a finished CLT structure can be maintained with just one-third the normally required heating or cooling energy.
A thick cross-section provides valuable and superior fire resistance for a CLT panel. Their mass means they char slowly, slowing and eventually stopping combustion.
With fewer concealed spaces, fire cannot spread undetected. Compared to concrete and steel structures in a catastrophic fire event, cross laminated timber structures suffer less degradation.
Moisture Management & Vapor Diffusion
Wood is naturally hygroscopic, serving as a moisture management system within a building envelope. Ideally manufactured at 12 percent moisture content, wood’s ability to absorb and emit moisture can naturally stabilize an indoor environment.
CLT buildings ‘breathe’, minimizing the risk for mold growth and maximizing the comfort of its occupants.
Healthy Indoor Environment
The only constituents of a CLT building system are wood and a non-toxic/non-VOC adhesive.
CLT building materials do not introduce any toxins into the indoor environment providing clean indoor air quality. Cross laminated timber wall systems are naturally breathable. Integrated with appropriate mechanical systems, this creates a healthy indoor environment that maximizes occupant comfort and health.
CLT has unique structural properties that provide increased design flexibility, allowing for distinctive and innovative projects.
Due to wood’s inherent ductility and unique strength to weight ratio, wood offers many advantages over the other common structural materials such as masonry, concrete, and steel.
Cross laminated timber panels are manufactured for specific end-use applications, which results in little to no job site waste. Plus, manufacturers can reuse fabrication scraps for stairs and other architectural elements.
Wood is the only major building material that grows naturally and is renewable. The longevity of CLT components ensures that the future value of any structure remains high. CLT buildings are easily altered and remodeled and are also fully recyclable once they reach the end of their useful life.
My company, SmartLam, partnered with the Montana DNRC to design and build bridging solutions to create environmentally friendly temporary bridges to access Montana State Lands for timber harvesting.
Our CLT bridging solution replaced the conventional stream crossings that required excavation of the streambed, placement of a culvert, and covering. The construction was less invasive, but no less durable.
The same standard applies to components within a structure, such as the multilevel building in Whitefish, Montana that specified a CLT elevator shaft. If the construction team was using poured concrete for the shaft, they would have had to budget for a process involving eight to 12 people, several inspections, added equipment to form and cure the shafts—and then a month to allow for the shafts to cure in place.
The CLT shaft was preassembled in a warehouse and assembled on site with just three people and a crane operator. The savings compared to concrete are in the neighborhood of 70 to 75 percent.
There’s no denying the most sustainable solutions are found in nature. And as we’re proving with CLT, sustainable solutions are stronger, more durable, and more affordable than many presume. A brighter, greener, future is well within reach.
Casey Malmquist is President and General Manager of SmartLam, and has served in this position since SmartLam’s inception in January of 2012. With more than 30 years’ experience owning and operating a successful construction and development company, he has led the SmartLam team from the ground level to becoming a globally-recognized producer of Cross-Laminated Timber products.