Cross Laminated Timber. Photo by the Oregon Department of Forestry, CC BY 2.0
Across the United States, any mass timber building designed to be taller than six stories high has to receive special approval from the building codes department. After a recent addendum was added to the Oregon’s building code, the state has become the first in the country to allow high rise mass timber buildings without receiving any special considerations.
It’s important to acknowledge the distinction between mass timber and more traditional wood buildings. Mass timber buildings, like this 12 story building in Quebec, Canada, have heavy duty and engineered wood structural elements, like cross laminated timber (CLT, pictured above). Environmentalists like the idea of mass timber projects, because it’s more a more sustainable product than concrete. Mass timber buildings can also be around 45% lighter than non-wood buildings, reducing load on foundations.
The new Oregon building code breaks mass timber into 3 classifications:
- Type IV A: up to 18 stories high and 270 feet tall
- Type IV B: up to 12 stories high and 180 feet tall
- Type IV C: up to 9 stories high and 85 feet tall
For type A buildings with fire sprinklers, all primary structural frame elements and bearing walls must be enclosed and provide 3 hours of fire resistance and floors must be 2-hour rated. Type C buildings are permitted to have exposed structural timber as a design element. The standards were developed and adopted from recommendations of the International Code Council’s (ICC) Ad Hoc Committee on Tall Wood Buildings, which was formed in 2015.
“This statewide alternate method intentionally reinforces the notion that the state building code is not a barrier to innovation or any method, technique or material of construction that is supported by scientific findings, while further preserving Oregon’s ability to serve as a single place to obtain statewide approval, providing a predictable regulatory system of business,” the addendum states.
Since Oregon is one of the country's leading timber producers, it's fitting that they would be the first state to approve the alternate construction type. America's "largest" mass timber building, in terms of square footage, was under construction in Oregon last December, but it only stands 5 stories high. It will be interesting to see if and how quickly other states follow in Oregon's footsteps.
Full Addendum: Statewide Alternate Method No. 18-01 Tall Wood Buildings | Oregon.gov
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