As an addition to one of North America’s top ten busiest airports, the C Concourse Expansion at Seattle-Tacoma International Airport (SEA) nearly triples the size of the concourse, creating a new destination through placemaking, sustainability, and signature architecture.
As passenger demand continues to grow, airports are facing increasing challenges to expand within constrained sites. At Seattle-Tacoma International Airport (SEA), limited land availability prompted a different design approach. Designed by Woods Bagot and The Miller Hull Partnership in collaboration with the Port of Seattle, the airport’s C Concourse Expansion demonstrates how vertical growth can increase capacity while enhancing the passenger experience.
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The project has seen the addition of four levels above one of SEA’s busiest concourses, creating new space for dining, retail, gathering and circulation without expanding the airport’s footprint. By building upwards, the design has transformed the airport’s existing infrastructure into a multi-level destination that supports both operational efficiency and traveler wellbeing.
Drawing on the character of the Pacific Northwest, the design strengthens the connection between travelers and place. Expansive glazing frames views of the surrounding landscape, while natural materials, abundant daylight and integrated public art create an environment that reflects the regional identity. At the heart of the expansion is the Tree at C, which anchors a two-story marketplace and social hub, creating an intuitive focal point for meeting, dining and relaxation.
The project places inclusivity and wellbeing at the center of the passenger journey, incorporating a sensory room, prayer and meditation space, a nursing room, pet relief area and additional spaces for quiet reflection.
“The C Concourse Expansion is shaped by the belief that travel environments should reflect both the spirit of place and the diversity of the people who move through them,” says Katy Mercer, Principal and Interior Design Leader, North America at Woods Bagot. “Our design creates a sequence of spaces that are intuitive, welcoming and grounded in the Pacific Northwest, offering moments of connection, pause and discovery throughout the journey.”
“SEA is one of the most space-constrained airports in the country while welcoming the eleventh largest number of passengers, so our teams had to get creative,” comments Airport Managing Director Wendy Reiter. “The C Concourse Expansion is the perfect illustration of creativity. We couldn’t go out, so we had to go up. Despite using the same footprint and not losing any gates, we’ve created more comfort and utility for our travelers.”
Sustainability was a focal point of the project. All-electric building systems, rooftop solar generation, electrochromic glazing and the adaptive reuse of significant portions of the existing concourse structure all help reduce both operational and embodied carbon. As SEA’s first project targeting LEED Platinum certification and implementing the Port of Seattle’s Sustainable Evaluation Framework, the expansion establishes a sustainable benchmark for the future of airport development.
“The C Concourse Expansion represents more than a new building for the Port of Seattle,” adds Port of Seattle Commission President Ryan Calkins. “It demonstrates what is possible when innovation, environmental leadership and partnership come together.”
The C Concourse Expansion demonstrates how airports can respond to growth through design innovation rather than physical sprawl, creating a more connected, sustainable and place-responsive experience for travelers.
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