Oregon first state to codify timber high-rises
- The Oregon Building Codes Division this month issued a statement of alternate method (SAM) introducing three new types of construction for tall wood buildings. The ruling makes Oregon the first U.S. state to allow construction of wood buildings taller than six stories without special consideration, according to the American Wood Council. The issuance of a statewide alternate method is reserved for "any material, design or method of construction" not already included in Oregon building codes — in this case, the "2014 Oregon Structural Specialty Code."
- The three new types of construction are included under the existing category of Type IV heavy timber construction. Contractors building Type IV A structures, which can go as high as 18 stories and 270 feet, must encapsulate exposed timber surfaces and, just like the other two types, must meet required fire resistance and fire safety requirements. Maximum height is determined by occupancy and use. Type IV B structures can be built as high as 12 stories and 180 feet and a percentage can have exposed timber surfaces. There are no restrictions on the percentage of exposed timber surfaces a Type IV C structure can have, and those buildings are allowed to be constructed to nine stories and 85 feet in height.
- As part of the SAM, the division said it wanted to drive home the point 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." The SAM is based on two years of development work by the International Code Council's (ICC) Ad Hoc Committee on Tall Wood Buildings and is written to be consistent with the use of cross-laminated timber and structural composite lumber.
Prior to tall wood construction being incorporated into Oregon state building codes, Portland, Oregon, was the first U.S. city to approve a construction permit for an all-wood building, the 12-story Framework. As part of the permitting process, since there was no building code yet for this type of construction, building officials verified through testing that the structure's proposed design and materials met the required fire, acoustic and structural performance standards.
The Framework project, however, which was to include 60 affordable housing units, is on indefinite hold due to general and construction cost inflation and uncertainty around tax credits.
Although counterintuitive to some, heavy timber construction does not present as much of a fire hazard as standard wood construction. In fact, advocates of wood construction maintain that heavy timber will char during a fire, creating a protective, flame-resistant outer layer around wood that helps members retain up to 90% of their original strength.
Now that Oregon has made the leap to authorize tall wood building construction, other states may follow suit.
- Oregon Building Codes Division Statewide Alternate Method No. 18-01 Tall Wood Buildings – Background
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