Oregon has become the first state in the U.S. to allow timber buildings to rise higher than six stories without special consideration. The recent addendum to the state's building code is the result of Oregon’s statewide alternate method (SAM), a program that allows for alternate building techniques to be used after an advisory council has approved the “technical and scientific facts of the proposed alternate method.” The decision stands as a precedent for future construction across the United States.
In April this year, an Ad Hoc Committee of the International Code Council presented their findings on timber high rise construction to the Oregon Codes Division. The committee was created in 2015 to explore the benefits and challenges of using timber in tall buildings. All 14 of the committee’s suggestions were adopted, including standards and best practices for the load-bearing potential of CLT and heavy timber, fireproofing, seismic rating, and more.
Three new building classifications were introduced: Type IV A, timber buildings permitted up to 18 stories and 270 feet tall, Type IV B, timber buildings with a maximum height of 12 stories and 180 feet, and Type IV C, which is permitted to rise nine stories and 85 feet tall at maximum. The tallest, type A, must enclose all exposed surfaces and include a three-hour fire-resistance rating for the structural elements. The shortest of the timber typologies is allowed to use exposed structural timber as an interior finish.
As interest in timber construction rises, Oregon's decision to allow tall timber buildings has the potential to impact building codes and standards across the country, especially those states where special considerations on timber high rises do not exist.