Designs have been approved for Carbon12, an 8 story building planned for N Williams Avenue. The designers of the project, PATH Architecture, expect that the 85′ tall structure will be the first tall building in the USA built using Cross-laminated Timber (CLT) as its structural system. The building will include 14 residential condominium units, as well as two ground floor retail units. With floorplates much skinnier than is typical in multifamily buildings Carbon12 will include only two residential units per floor. 22 parking spaces will be provided in a below grade mechanized parking system.
Carbon12 will be located at the corner of N Williams Ave and NE Fremont St, on a site that is currently vacant. In 2013 the site was rezoned at the request of the property owner from Multi-Dwelling Residential 1,000 (R1) to Central Residential (RX). The rezoning was initiated so that a project could be developed with ground floor commercial uses, which are prohibited in the R1 zone. As a condition of approval the City Council set a maximum height of 85′ for the corner of the site, stepping down to 65′ for most of the site and to 45′ adjacent to the R2 zoned properties. This is less than the 100′ height normally allowed in an RX zone, but more than the 65′ height allowed in the EX zone applied along most of N Williams Ave.
Building codes typically limit structures built using light wood framing to five or six stories, however Cross-laminated Timber construction allows for much taller buildings. The CLT panels are made by gluing together many smaller pieces into a larger assembly that has sometimes been described as “plywood on steroids”. As well as having much greater strength than wood members, heavy timber is also considered more fire resistant. Though still considered experimental in the USA the process has been used in Europe since in 1990s. A 10 story CLT structure was recently completed in London and an 18 story structure is under construction at the University of British Columbia in Vancouver. Late last year D.R. Johnson, an Oregon lumber mill, became the first mill in the USA certified as able produce CLT.
The primary exterior materials for the building will be a curtain wall glazing system and metal paneling. Stucco will be used around the inset balconies. Vertical wood fins will accentuate the lower floors where they face the street.
The project’s Design Review was approved through a Type II review, where the decision is made by Bureau of Development Services staff. In the Notice of Decision [PDF] it was noted that the structural system chosen allows for an architectural expression uncommon in wood framed buildings:
Architecturally, the building is modern in style expressing clean lines and simplicity. The materials were chosen to be distinctive and reflect some qualities of the nearby buildings…. The proposal’s wide timber structural bays allow for windows much broader than is typical in midrise commercial wood buildings. This allows for greater transparency and views of the interior wood beams, posts and ceiling from the exterior.
Building permits for Carbon12 are currently under review. Due to the pioneering nature of the project the structural and life safety reviews are being conducted by the State of Oregon Building Codes Division, rather than by the City of Portland who would usually perform the review. Construction is expected to begin later this year.