Cross Laminated Timber – An Emerging Structural Material for Taller Wood BuildingsOct 22 2015 · 0 comments · NISHKIAN DEAN, Wood Frame ·0
Cross-laminated timber (CLT) continues to receive more attention nationally and locally as an innovative and economical solution for utilizing wood construction in taller buildings. While multi-story CLT buildings have been constructed in Europe, Canada, and Australia over the past 20 years, its use as a primary building material in the United States is still in the early stages of development.
CLT may also be classified as mass timber construction, which is building construction that uses large prefabricated wood panel members such as CLT and engineered wood for wall, floor, and roof construction. Glulam material may also be used in beam and column applications.
CLT was originally developed in Switzerland in the early 1990s and panels consist of multiple layers of wood with each layer oriented crosswise to the next. Finished CLT panels are typically 2 to 10 feet wide, with lengths up to 60 feet and thickness up to 20 inches. This allows it to be used for long spans in floors, walls, or roofing. CLT is also fast and easy to install, generating almost no waste on the job site. Panel to panel connections are made with wood screws and light gage or steel connectors. CLT is lightweight yet very strong, with superior acoustic, fire, and thermal performance. It also offers design flexibility and low environmental impacts. For these reasons, cross-laminated timber is proving to be an advantageous alternative to conventional materials like concrete, masonry, or steel; particularly in multi-family and commercial construction.
State of Oregon adopts upcoming Building Code for CLT
As of January, 2015, the State for Oregon Building Codes Division has approved a statewide alternate method (No. 15-01) that will allow the use of CLT for Type IV, Heavy Timber buildings, a construction type that utilizes larger, exposed wood structural members that have minimum sizes for code required fire-resistive requirements. Currently, Oregon is the only US state to have formally adopted the use of CLT as a Heavy Timber component. The alternate method can be found here: http://bcd.oregon.gov/programs/structural/alt_methods/15-01_Cross_Laminated_Timber_SAM.pdf
This alternate method adopts provisions of the 2015 International Building Code (IBC) for designing CLT buildings, which is expected to be fully adopted by 2017 in Oregon. The current building code in Oregon is the 2014 Oregon Structural Specialty Code (OSSC), which is based on the 2012 IBC, and does not recognize CLT to be used under Heavy Timber construction. The 2015 IBC allows CLT panels to be used as shearwalls to resist lateral forces (seismic and wind). The seismic parameters included in the 2015 IBC are considered to somewhat conservative values until final testing and analysis required are completed in the near future. The updated values will soon be published as part of the Federal Emergency Management Agency (FEMA) document P-695, Quantification of Seismic Performance Factors, a document prepared by a task force developed by the Applied Technology Council (ATC).
The American Plywood Association (APA) has a published document, ANSI/APA PRG 320-2012, Standard for Performance Rated Cross-Laminated Timber, which serves as the US standard for CLT. This document provides structural grading classifications, design values, and requirements and test methods for qualification and quality assurance.
CLT Being Put to Use in Oregon
Oregon BEST, an agency focused on clean technology innovation, recently announced a CLT design contest that would award up to $200,000 in funds for an innovative and viable building project that best demonstrates the aesthetics and structural use of CLT.
At the recent annual Oregon BEST annual conference, Governor Kate Brown declared, “CLT presents a new and exciting opportunity for Oregon. Expanding new industries and innovative technologies like advanced wood manufacturing will help reinvigorate our rural, timber-focused economies.”
D.R. Johnson Wood Innovations located in Riddle, OR recently became the first manufacturer in the United States to receive certification from the American Plywood Association (APA) to produce cross-laminated timber. Currently, the maximum panel size that can be produced at their facility is 10’x24’x 3, 5, or 7 layers. More information is available on their website.
The City of Portland also made headlines when Lever Architecture was announced as the west coast winner of the U.S. Tall Wood Building Competition. Lever will design a twelve-story, mixed-use building, which will be located in the popular Pearl District, utilizing CLT as the primary structural material.
The first permitted CLT project in Oregon was a small visitor building at the Oregon Zoo in Portland completed in 2014. Upcoming CLT projects in Oregon include a building at Western Oregon University and the Lever building in the Pearl District. Nishkian Dean has recently designed a 2-story CLT residential structure utilizing exposed wall and roof panels, which has been submitted for permit approval in the City of Portland. To learn more about this and our other projects, please see our website or contact us at firstname.lastname@example.org.