In the limited footprint that is Seattle-Tacoma International Airport (SEA), the Port of Seattle needed to go vertical to expand the C Concourse from 114,000 square feet to more than 229,500 square feet.
Led by Turner Construction as the construction general contractor, the project created an additional four floors above an existing lobby building in the back office footprint. Work began in the summer of 2022 and major construction began in 2024, culminating in the June 11 opening of the $399 million project financed by a combination of the Airport Development Fund and future revenue bonds. No taxpayer money was used.
“SEA is one of the most space-constrained airports in the country, while serving the 11th largest number of passengers,” says Wendy Reiter, CEO of SEA. “Our teams had to be creative. We couldn’t go out, so we had to go up. With the same footprint and without losing a door, we’ve created more comfort and utility for our travelers.”
The connection between concourses C and D, traditionally very congested, is now bright with daylight and 10 new retail and dining spaces. The all-electric project created grand staircases to connect the new lobby level with a mezzanine with a dining room. The return stairs, inspired by a hiking trail, link to level three, which includes an outdoor gazebo at C with an outdoor wooden and basalt stone deck with views of the airfield and the Olympic mountains. Levels four and five include flexible spaces for lounges and offices. During construction, the port was able to maximize daylight and view corridors.
The main lobby floor, created from regionally quarried terrazzo stone, forms the base of a stepped atrium, an amphitheater-like open space with a live music area, framed by restaurants and retail called Marketplace at C. Located near the C2 gates that welcome flights of busy travelers, the atrium is inspired by local outdoor markets, particularly Pike Place. There is a new 20,000 square foot Alaska Airlines Lounge, office space and the potential for further expansion.
“This project was really in the middle of a very, very busy airfield,” says Janet Sheerer, the port’s project manager.
The Tree at C provides the most visually striking component of the project, an artistic way to elevate the western hemlock roof of the new building and highlight the triangular timber roof. Inspired by the folded exterior facade, the wooden “tree trunk” solved the challenge of integrating structural columns into the design while ensuring a canopy-like aesthetic to the meeting space. The trunk reaches from the floor to the 30-foot ceiling halfway up the grand staircase.
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“The Tree at C” works both aesthetically and structurally within the extended room.
Photo courtesy of the Port of Seattle
“The idea came through iteration and the more we sketched it out, we saw that it was in a sweet spot: the way the circulation passed around it and the way the grand staircases sunk into this mezzanine level,” says Billy Schreiber, project leader at Woods Bagot, who worked with The Miller Hull Partnership on the design.
Kevin Stilwell, vice president and construction executive at Turner, says airports serve as gateways to communities and the C Concourse expansion “gives passengers more opportunities” to welcome the Pacific Northwest.
A folded exterior facade, patterned in the forests of the Pacific Northwest, wraps the southwest exposure with alternating south- and west-facing panes of dynamically tinted glass. The 5-foot-wide glass panels come in pairs, minimizing columns. The roof slopes at a Federal Aviation Administration-prescribed angle to the runways to maximize interior volume while maintaining a photovoltaic array designed to produce up to 14% of the facility’s power, all part of the port’s sustainable effort to aim for LEED Platinum, the highest certification of any SEA facility.
