Oregon becomes first state in the U.S.to legalise mass timber high rises

Oregon became the first state in the U.S. to allow timber buildings to rise higher than six storeys without special consideration, due to a recent addendum to Oregon’s building code, reported the Architects Newspaper. 

Timber innovation has been trending of late in Portland, where several high-rise timber buildings have been erected such as the Carbon12, PATH Architecture’s eight-storey glulam and cross-laminated timber (CLT) tower with a steel core which recently became the country’s tallest timber building and also LEVER Architecture’s 12-storey framework, which was recently put on hold.

The timber allowance came to fruition thanks to Oregon’s state-wide alternate method (SAM), a state-specific programme that gives experimental space for alternate building techniques to be used after an advisory council has approved the “technical and scientific facts of the proposed alternate method.” It was also made possible after the International Code Council (ICC)–the non-profit group that Oregon models its building codes after–established the ICC Ad Hoc Committee on Tall Wood Buildings in 2015 to explore the benefits and challenges of using timber in tall buildings.

A Committee Action Hearing was held in April this year, where the Ad Hoc Committee, made up of code experts, stakeholders, and industry members presented their findings and 14 recommendations, all of which were adopted. The suggestions included introducing standards and best practices for fireproofing, the load-bearing potential of CLT and heavy timber, water resistance, sealing, seismic ratings.

Three new building classifications were also introduced: Type IV A, timber buildings permitted up to 18 storeys and 270 feet tall; Type IV B, timber buildings with a maximum height of 12 storeys and 180 feet; and Type IV C, which is permitted to rise nine storeys and 85 feet tall at maximum. The shortest of the timber typologies is allowed to use exposed structural timber as an interior finish, whereas the tallest, type A, must conceal all exposed surfaces and include a three-hour fire-resistance rating for the structural elements.

“We congratulate the State of Oregon on becoming the first state to provide building code recognition for construction of tall, mass timber buildings,” said American Wood Council President & CEO Robert Glowinski.

“Mass timber is a new category of wood products that will revolutionise how America builds and we’ve seen interest in it continue to grow over the last several years. This action by the Codes Division Administrator helps code officials in Oregon by making provisions consistent throughout the state. In adopting this new method, Oregon has also recognised the significant environmental benefits that accrue from greater wood product use.”