Over the last few years, one topic has captured more attention with engineers, architects and wood enthusiasts worldwide than any other: Cross Laminated Timber (CLT). CLT is often described as plywood on steroids because it is made by gluing alternating layers of lumber together to make a thick panel, much like the layers of veneer in plywood. CLT is part of a bigger initiative known as Mass Timber Construction (MTC), which is exactly what it sounds like – really big chunks of wood-based products. What makes MTC interesting is that these massive wood sections are suitable for competing with concrete, masonry, and steel construction in midrise (7-15 story) and taller (up to 40 story) buildings where wood typically is not considered feasible. If you have the time, Architect Michael Green’s TED talk on why we should build wooden skyscrapers is a great introduction to the possibilities for expanding wood construction into tall buildings. It’s hard to hear his message without becoming excited about the future of wood.
Distinct advantages for MTC range from the feel good story of carbon storage, reduced greenhouse gas emissions and lower embodied energy in manufacturing, to the financial benefits of reduced foundation sizes and shortened construction cycles. Sounds good, so why aren’t tall wooden buildings showing up all over North America? Good question. There are a handful of tall MTC buildings in Europe and Australia, but very few in North America at present. Many point to concerns with fire performance as the key hurdle, but testing conducted by researchers indicates that the panels develop a protective char layer and maintain their structural integrity if properly designed. Other technical challenges include building code limitations on heights and areas for combustible construction materials, lack of detailed seismic design information, and a need for general system and connection design guidance. The wood industry is working to overcome these and other technical challenges, as an example CLT is now included in the upcoming ANSI/AWC NDS-2015 edition, but one significant gap remains – a lack of developers interested in MTC buildings. The USDA, in cooperation with the Softwood Lumber Board and Binational Softwood Lumber Council, is trying to fix that with the recently announced U.S. Tall Wood Building Prize Competition. If all goes as intended, this initiative will lead to the first modern tall wood building (80 feet or greater) in the U.S. and will serve as a demonstration project fueling future development.
I’ve followed this topic for a few years now and have been asked many times where Engineered Wood Products (EWP) fit in the MTC revolution given that so much emphasis is placed on CLT. One of the first modern tall MTC buildings in North America, the Earth Systems Science Building on the University of British Columbia campus shown in the photo above, utilized our TimberStrand® LSL technology in large panel sections as part of a hybrid timber-concrete floor system. Additionally, academic research is ongoing to study other hybrid composite systems and CLT utilizing EWP laminates to improve strength. Other technologies like our Parallam® PSL beams and columns are a natural fit as well given their availability in large sections and long lengths. So what’s the answer? I believe that while CLT gets most of the current attention, the future lies in the innovative combinations of materials into efficient and cost-effective systems and CLT, hybrid CLT composites and EWP will each play a role.
We are a long way from a mass timber revolution, but it appears that momentum is slowly building toward a future where our skylines include a few iconic MTC structures alongside their steel and concrete peers. If you are interested in more information about MTC, I suggest one of the many online or hosted events from WoodWorks, and if you would like to learn more about using Trus Joist EWP products in MTC, our technical support team is ready to help.