35 AirportImprovement.com September 2026 TERMINALS SEA Expansion. While many airports add space by expanding outward, SEA had to get creative. “We couldn’t build out, so we built up,” Reiter says. The joint design team of The Miller Hull Partnership and Woods Bagot stacked new public spaces vertically above the existing structure, creating an open, light- filled space that now serves as the heart of the C and D concourses. For Reiter, the project reflects a broader vision of the airport’s future. “This is truly what we wanted to see for SEA—a place where you feel at home and you get a feeling of space.” A Place to Linger Anchoring the center of the new space are the Grand Stairs and the Tree at C, a sculpted architectural element sheathed in locally sourced Western Hemlock that rises from the midpoint of the extra-wide staircase and connects physically and blends visually with the wood-veneer acoustic ceiling. (See photo above). The staircase is peppered with 15 illuminated boxes that feature various works by three Pacific Northwest artists. Together, the features encourage passengers to look up and explore the restaurants, gathering spaces and public lookout on the third floor. The 20-foot-tall Tree at C was a collaboration of architects Woods Bagot and The Miller Hull Partnership for design, Armstrong World Industries for building materials, and Acoustical Design Inc. for construction. “Hardly anyone wanted to tackle the ‘Tree at C,’ but we did,” says Travis Styer, senior project manager, Northwest Region, for Armstrong. “We had great partners in Seattle, and we all respected the importance of this project to the city and beyond. The extraordinary results are a testament to early planning, engineering and collaboration.” TRAVIS STYER FACTS&FIGURES Project: Concourse Expansion Location: Seattle-Tacoma Int’l Airport, in WA Concourse: C Scope: 148,500 sq. ft. of new space over 4 floors Noteworthy Features: Central gathering space known as the “Tree at C” with area for live entertainment; “Lookout at C” observation deck with views of airfield & Olympic Mountains Amenities: Sensory room, interfaith prayer & meditation room, nursing room, pet relief area Sustainability Features: Electrochromic glazing; solar panels; all-electric systems Budget: $399 million Funding: Airport Development Fund; future revenue bonds Timeline: Design authorization in 2020; construction began mid 2023; facility opened June 11, 2026 Program Manager: Port of Seattle Architects: The Miller Hull Partnership; Woods Bagot General Contractor/Construction Manager: Turner Construction Civil & Structural Engineering: Magnusson Klemencic Associates | MKA-Seattle Mechanical, Electrical & Plumbing Engineering: PAE Engineers; ARUP Ceiling/Tree Design: The Miller Hull Partnership; Woods Bagot Ceiling/Tree Materials: Armstrong World Industries Ceiling/Tree Construction: Acoustical Design Inc. Electrochromic Glazing: SageGlass Photovoltaic Panel Manufacturer: SolarEdge Lighting Design: Dark Light Design
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