Cross Laminated Timber
Cross laminated timber (CLT) is an engineered wood building system designed to complement light- and heavy-timber framing options. CLT panels are made by gluing together layer after layer of dimensional lumber, such as 2-by-4s, 2-by-6s or other dimensions, at 90 degree angles and pressing it into a thick panel. The panels can be up to 10 feet wide by 60 feet long and up to 18 inches thick.
Cross Laminated Timber Blocks
Because of its high strength and dimensional stability, CLT can be used as an alternative to concrete, masonry and steel in many building types. It can be used for an entire building, as both the lateral and vertical load-resisting systems, or for select elements such as the roof, floors, or walls. Furthermore, what makes CLT unique is that it is as strong as steel and up to 5x lighter than concrete, which is perfect for high-rises. However, there is a limit of how high you can build with a CLT high-rise.
As a cost-effective, green high-rise building block, CLT has a much smaller carbon footprint than concrete and steel. Concrete emits carbon that is detrimental to the environment. Wood has a lighter carbon footprint because wood products continue to store carbon absorbed by the trees while growing, and wood manufacturing requires less energy and results in less greenhouse gas emissions.
CLT panels are manufactured for specific applications. They are prefabricated, complete with pre-cut openings for doors, windows, stairs, service channels and ducts, and shipped directly from the manufacturer to the job site, where they can be quickly and efficiently lifted into place. This can shave months off the construction schedule.
Some benefits to using Cross Laminated Timber (CLT) are:
- Speed and efficiency of installation
- Design flexibility
- Cost competitiveness
- Seismic performance
- Thermal performance and energy efficiency
- Environmental performance
- Resource efficiency
CLT is manufactured using wood from sustainably managed forests. The massive building panels often times use lumber from thin trees that are susceptible to pest outbreaks and pose catastrophic fire threats. There is also very little resource waste as smaller dimensional material can be used to make CLT panels that might not otherwise be used in other structural applications. Additionally, CLT panels are manufactured specifically for each project and any fabrication scraps can be used for stairs or other architectural elements.
CLT & Fire Resistance
CLT’s thick cross-section provides valuable fire resistance because panels char slowly. Once formed, char protects the wood from further degradation. In addition, CLT offers increased compartmentalization if used for interior walls. Due to the inherent nature of thick timber members to slowly char at a predictable rate, CLT panels can maintain significant structural capacity for an extended duration of time when exposed to fire. "People don't realize that wood has an inherent fire resistance when it's actually large, and it doesn't lose its strength as it burns," says architect Thomas Robinson.
International Recognition & North America
CLT has been popular in Europe for more than 20 years, with extensive research and a documented track record supporting its widespread use. Internationally, it has propelled wood construction to new heights, the most recent example of which is the Forté, a 10-story CLT apartment building in Australia. It offers the structural simplicity needed for cost-effective projects, as well as benefits such as design versatility, rapid installation, reduced waste, lighter weight (compared to concrete), and energy efficiency.
In North America, CLT is relatively new but quickly gaining momentum. Last year, the American National Standards Association approved ANSI/APA PRG 320-2012 Standard for Performance-Rated Cross-Laminated Timber, a product standard that details manufacturing and performance requirements for qualification and quality assurance. Thanks to recently approved code changes, CLT is also scheduled to be included in the 2015 International Building Code (IBC). In the meantime, a handful of innovative designers have already built CLT structures in the U.S. and Canada, having had them approved under their local building code as an alternative building system.
CLT’s strength, structural performance and cost-competitiveness are expanding opportunities for the use of wood in a wider range of buildings. Available in North America and increasingly accepted under building codes, it provides a flexible, sustainable and efficient alternative to concrete and steel for many applications.