Mass Timber Conference 2018
On March 22-23, 2018 three representatives from Caron Architecture attended the Mass Timber conference in Portland, Oregon. There were over 1200 people in attendance from various backgrounds including architects, engineers, government officials, contractors, and timber industry representatives. One of the main subjects was Cross Laminated Timber (CLT). CLT is a built-up lumber product comprised of standard 2x lumber pieces glued together side by side flat-wise and subsequent layers or laminations of lumber laid and glued perpendicular to the first. The end result is a large wood panel of either 3 or 5 laminations that is akin to heavy timber construction, but has the properties of a rigid diaphragm, such as a reinforced concrete.
Portland mayor Ted Wheeler gave a great keynote speech about the history of Oregon and its role in the timber industry, and how that resonates today and into the future of wood-structured buildings. The conference included 4 different seminar tracks, each of which had an enormous amount of helpful information.
There were highlights we noted both on the policy side and the technical side regarding the use of CLT in construction today and in the future:
Policy highlights include:
- The upcoming 2021 IBC update will maintain the current Type IV construction section under “HT”, and then add 3 new sections (A, B and C) to Type IV to address timber-framed high-rises of various heights up to 18 stories.
- For energy code, timber tends to perform better than concrete or steel when evaluating flanking paths and thermal bridging.
- CLT has potential for carbon sequestration and reducing use of carbon-emitting concrete and steel construction.
- Given the current international trade climate, CLT may have the benefit of being produced locally and may compete with steel prices that are affected by tariffs.
Technical highlights include:
- State universities, particularly Oregon State and Washington State, are leading the way on testing for structural capacity of CLT as well as fire rating performance and sound rating performance. CLT has the capacity to perform very well in a seismic event with proper detailing.
- Connections are critical in making CLT work in a structural capacity. The connections also cost the most to analyze. The connections used in CLT are still being developed, and as CLT becomes more prevalent, more efficient effective details will emerge. Screws, fasteners and plates are all being analyzed by engineers and universities for the best use with CLT. Screws up to 59” long have been used in mass timber projects!
- Architects and engineers are coming up with very innovative composite construction systems to take advantage of CLT as a seismic resisting system, as well as an aesthetic choice, including CLT with concrete topping slabs, CLT-steel braced frames and more.
- Moisture and insects are a serious concern with wood structures and the glues used to adhere CLT. Studies of their impacts are ongoing, particularly with coatings and invasive termite species in warmer climates. Protection of wood during construction is critical! End grain can absorb moisture up to 20x faster.
- State and local laws should be reviewed for 3rd party inspection requirements during fabrication.