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Washington building codes changed to allow taller mass timber buildings

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Washington became the first state in the nation to allow tall mass timber buildings when the State Building Code Council (SBCC) approved changes allowing builders to go as high as 18 stories using such material. Previously, such use was limited to six stories.

The code changes were approved November 30 and are scheduled to go into effect at the conclusion of this year’s Washington State Legislative Session, slated for April 28.

In a statement applauding the change, Forterra president and CEO Michelle Connor stated, “As mass timber becomes more widely utilized, it has great potential to support employment in rural areas, improve forest health on public lands in need of restoration, and enable new and affordable approaches to building for fast-growing urban populations. These code changes will allow for greater use of mass timber here in Washington, and position our state as a leader in the nation.”

Forterra, a nonprofit that secures land for a sustainable future, led a four-year effort by a statewide coalition of more than a dozen organizations to advance the code changes.

“The changes approved by the SBCC will provide an increased opportunity to use Washington-based wood products in building projects across the state,” says Jeffrey Hamlett, executive director of AIA Washington Council. “We applaud the SBCC for passing these amendments and look forward to enjoying the creative challenges and benefiting from the aesthetic and carbon-related advantages of designing taller buildings made with wood.”

Mass timber is a category of large-scale, prefabricated engineered wood products, the best-known of which is Cross Laminated Timber (CLT). CLT panels are comprised of multiple layers of lumber, each stacked perpendicularly and bonded with a structural adhesive. Advocates say the result is a beautiful, lightweight, and durable building material with favorable fire, seismic and thermal performance. European architecture has been utilizing CLT for more than two decades.

Washington’s code changes will update the IBC 2015 to incorporate all of the International Code Council’s Tall Wood Building Code proposals voted on in Richmond, Virginia last October. It will permit three new types of mass timber building construction – Type IV A, B, C – allowing for the structural use of mass timber at 18, 12, and 9 stories. The action comes after more than two years of comprehensive research and testing, including full-scale fire tests, completed by the International Code Council Ad Hoc Committee on Tall Wood Buildings. Currently, the building code limits mass timber’s structural use to a maximum of six stories.

Several mass-timber projects below six stories have been completed in Washington in recent years, including a set of pilot CLT classrooms funded by the State of Washington. Now, with approval of the IBC changes, taller wood projects like Brock Commons Tallwood House at the University of British Columbia can move forward. Forterra described CLT as great for rapid modular construction, noting it took less than 70 days for the 18-story wood hybrid Brock Commons (called “Plyscraper” by some) building to be completed after the prefabricated components arrived on site-four months faster than an average project of this size.

Architect Susan Jones of atelierjones said the code changes will allow Washington to embrace more innovative construction practices and lead the nation in long-term sustainable building. “I am so proud of my state of Washington. As a third-generation Washingtonian, who grew up amongst its forests, I am deeply optimistic about the impact these code changes will have on our forests’ health and long-term sustainability,” who lives in a home she designed using CLT.

Jason Callahan, director of governmental relations at the Washington Forest Protection Association, said, “We are excited about any action that leads to incentives for wood and wood products. Support for wood products helps Washington move closer to its climate goals, while also providing other ecosystem benefits.”

Technically, Oregon became the first state in the country to allow timber buildings to rise higher than six stories without special consideration when that state’s Building Codes Division announced a “statement of alternate method” (SAM) addendum to its code last August. Washington is the first state to allow tall mass timber buildings through its regular building code.

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