Miller Hull and Woods Bagot Unveil Major Concourse Expansion at Seattle-Tacoma International Airport

Seattle-Tacoma International Airport (SEA) has officially opened its $400 million C-Concourse Expansion, a significant project led by The Miller Hull Partnership and Woods Bagot. The expansion dramatically increases the concourse’s footprint and introduces a range of sustainable and passenger-centric features, aiming for LEED Platinum certification.

New Height and Area

The C-Concourse Expansion adds four new floors between the airport’s existing C and D concourses. This vertical expansion increased the concourse area from 81,000 square feet to approximately 230,000 square feet. Airport officials noted that SEA is one of the most space-constrained airports nationally, making upward expansion the most viable strategy. The area for the expansion was previously restricted to airport personnel.

Sustainable Innovations

A core focus of the expansion is its commitment to sustainability. The project is SEA Airport’s first all-electric building and features the airport’s inaugural airside public outdoor space. The distinctive, slanted roof is topped with solar panels, marking the first installation of photovoltaics at the airport. These panels contribute to the building’s energy efficiency and its goal of achieving LEED Platinum certification.

Design Inspired by the Region

The architectural design, characterized by an accordion-shaped plan for its glass windows and roofline, filters polychromatic light into a new central atrium. This atrium is anchored by a grand staircase and a prominent wooden sculptural component dubbed “The Tree at C.” The design draws inspiration from the biophilic principles prevalent in Pacific Northwest architecture, aiming to connect travelers with the region’s natural beauty. Miller Hull highlighted that the 2-story atrium’s design echoes the marketplaces of Seattle, referencing the firm’s previous expansion of Pike Place Market.

Passenger Experience Enhancements

Beyond its structural and sustainable advancements, the expansion introduces new amenities designed to improve the passenger experience. These include a sensory room, an interfaith prayer and meditation room, and a nursing room. The mezzanine level offers views of the airfield, while the atrium’s design aims to create an authentic sense of place and belonging for all travelers.

Reflecting Place and Collaboration

Principals from both design firms emphasized the project’s role in reflecting the community and the collaborative process. Katy Mercer, a principal at Woods Bagot, stated that the C Concourse Expansion serves as “more than just a transit hub,” but rather “a reflection of the world it serves and the collaborative processes behind it.” Rich Whealan, a principal at Miller Hull, added that the design seeks to immerse passengers in the Pacific Northwest’s natural environment, with the concourse’s interior lighting responding to the dynamic regional light conditions.

Key facts

This development is significant for architecture enthusiasts and professionals as it showcases a major public infrastructure project integrating advanced sustainable technologies and regionally inspired design principles. The expansion at SEA Airport serves as a model for how large-scale transportation hubs can enhance passenger experience while prioritizing environmental responsibility.

Source: The Architect’s Newspaper, https://www.archpaper.com/2026/07/miller-hull-woods-bagot-seattle-tacoma-international-airport/