Architecture studios The Miller Hull Partnership and Woods Bagot have completed an extension to Concourse C at Seattle-Tacoma International Airport, integrating a large timber-clad "tree" that arches over a gathering space.

In collaboration with the Port of Seattle, the C Concourse Expansion (CCE) is one of several major projects planned for upgrading Seattle-Tacoma International Airport (SEA) under the Upgrade SEA initiative launched in 2023.

The expansion spans Concourse C, as well as parts of Concourse D and more than doubles the size of the existing buildings by adding four new floors.

The final building is wedge-shaped, with a slightly sloping roof covered in photovoltaic panels and a crinkled glass facade.

The alternating south- and west-facing glass panels were made with electrochromic glass to minimise glare and optimise daylight, according to the team.

"As the day progresses, the concourse responds to the changing light and weather of the Pacific Northwest," said The Miller Hull Partnership principal Rich Whealan.

"On overcast, cloud-rich days, visibility is maximised to highlight the views of the airfield and Olympic Range, while soft, even daylight fills the interior, enhancing comfort and connecting travellers to the surrounding landscape."

Inside, the building is organised around a large "marketplace" area, which contains stadium seating and a large column covered in timber panelling that expands onto the ceiling.

Dubbed the Tree at C, the structure references the forests of the Pacific Northwest, according to the team, and is made of natural materials sourced from the region.

Food and shopping kiosks surround the area, while the central staircase and Tree were designed as a "point of orientation and a place to linger".

The expansion also includes an open-air lookout terrace, which is located in one corner of the building on the upper levels and faces the airstrip,

It is enclosed in glass along its walls and covered by the photovoltaic panels overhead.

The project integrates "several firsts for SEA", including the airport's first photovoltaic panels, first all-electric systems, and will be the first to target LEED Platinum certification.

Other updates completed at the airport include widened roadways and a more efficient baggage system, while an update to the building's international terminal is still in the design phase.

Woods Bagot has completed two other recent airport projects at LAX and the Western Sydney International Airport, both of which feature timber panelling.

Miller Hull Partnership more recently renovated a Brutalist university library in California.

The photography is by Ema Peter Photography

Project credits:
Architects: The Miller Hull Partnership, LLP and Woods Bagot
General contractor and construction manager: Turner Construction Company
Structural and civil engineering: Magnusson Klemencic Associates
Mechanical and plumbing engineering and sustainability: PAE Engineers
Electrical engineering, smoke control, airfield civil and logistics, facades, facades access and maintenance, terminal-wide voice paging systems, acoustics: Arup
Airport dining and retail consultant: AirProjects
IT, Communications & Security: TLC Engineering Solutions
Wayfinding & signage: Mayer/Reed, Inc
Lighting design: Dark Light Design
Acoustics & vertical transportation: The Greenbusch Group, Inc.
Geotechnical engineering: Haley & Aldrich, Inc.
Cost advice: Cumming Group
Code Compliance & fire protection: Jensen Hughes
Site investigations & surveying: Holt Services