Engineered Artistry: The Armstrong Western Hemlock Tree at Seattle-Tacoma International Airport C Concourse

The Vision: Rethinking, reinventing, reinvigorating the airport experience

The Port of Seattle was depending on the design of the expanded C Concourse at Seattle-Tacoma International Airport (SEA) to create an intuitive journey as well as welcome every guest into a biophilic, climate-conscious space and immerse them in a sense of calm. From the start, it was critical for the ceilings, walls, and "Tree at C" to come together to provide an authentic Pacific Northwest experience. Plus, with the project schedule demanding completion in time to welcome 2026 FIFA World Cup fans, the C Concourse design was charged with making a bold statement that would inspire return visits from travelers across the country and around the globe.

"This is the kind of project that demonstrates who we are as a region," said Ryan Calkins, Commission President, Port of Seattle. "Travelers will see just an amazing sight where you get a sense of the great outdoors here, but also some of the hospitality of the Pacific Northwest."

The Challenge: Transforming a structural necessity into an architectural centerpiece

The tiered, open amphitheater-type layout of the main gathering area of the C Concourse required a large-format ceiling of approximately 4,600 square feet. A structural column disrupting that space posed a huge challenge to a design needing to represent the natural landscapes of the Pacific Northwest, convey the ceaseless energy and vibrancy of Seattle, and draw visitors up the grand staircase to second-level amenities.

"That column needed to be there, and because it broke up the project's largest open gathering space, a standard cover wasn't an option," said Billy Schreiber, Project Leader, Woods Bagot. "The team's opportunity was to create an elegant solution that celebrated the column rather than concealed it, transforming a structural necessity into a memorable feature of the space."

The decision to reinvent the column as the "Tree at C" brought its own set of challenges. It had to be engineered, structurally sound, and breathtaking. Its base had to integrate seamlessly with the grand stair, while its curved upper "branches" needed to blend naturally into the flat ceiling plane. And all this fluency-for the "Tree at C," the massive open ceiling, and ceiling-to-wall transitions-needed to be achieved in accordance with design renderings depicting triangular, natural wood panels, and purposeful reveals.

"There was no question this was a completely custom project, a one-off with nothing like it coming before or after," said Dan Holdridge, Senior Manager for PROJECTWORKS, Armstrong. "We tested and retested and made tweaks. We had all-in collaboration and clear communications the whole way through. Everything went smoothly and the results are incredible."

The large open space with its consistent flow of traffic also presented steep acoustical challenges requiring a carefully coordinate approach to achieve the project's acoustic performance goals while maintaining passenger comfort and clear voice-paging communications. In addition, everything from pre-construction planning to installation had to be conscientious of the June 2026 opening and the fact that work would happen in and around a fully operational airport.

Lastly, with the C Concourse making the region's first impression on well over a hundred thousand national and international visitors daily, the Port of Seattle stayed deeply involved in project oversight and approvals. With strong local ties, the architect, contractor, subcontractor, and Armstrong were all dedicated to ensuring the C Concourse Expansion would support Seattle-Tacoma's travel and tourism, economy, and people.

The Solution: Innovation. Customization. Collaboration. Repeat.

The solutions to the C Concourse expansion challenges started with the central product from Armstrong-custom triangular WOODWORKS ACGI Microperf ceiling panels in Western Hemlock. These panels allowed the ceiling and "Tree at C" to be designed to the architectural drawings, honored the Pacific Northwest landscape, and provided strong acoustical performance.

The "Tree at C" took an all-hands-on-deck approach. Armstrong leveraged a relationship with Devco Engineering to support the design of interior framework that would remain sound under the weight of more than 200 WOODWORKS panels. Each team's unique set of design and construction experience, product knowledge, and resources, ultimately lead to an approach for mounting the panels up the tree in a way that achieved necessary transitions into the ceiling. The structure consisted of curved steel tubing around the column which mounted back to it with Unistrut, steel rings, and hundreds of descending rods supporting the weight of the rings.

"Once we had the general idea, we started to break down the problems of changing situations as you advanced up the tree," said James Chaney, Senior Project Manager, Acoustical Design Inc (ADI). "At a certain point we could no longer rely on mounting back to the column. Even with precision calculations of weight and space to determine the proper Unistrut system, we still had 'hot spots' to solve for. The only way to make it work was by doing what we did-bringing all the teams together to collaborate."

Given the complexity of the "Tree at C" and its ceiling transition, Armstrong and ADI took the lead in creating three mockups that were progressively more realistic to the final product. The first two happened at ACGI and Armstrong manufacturing facilities, with the final "fit-and-finish" mockup occurring at the ADI warehouse. About 20 people came to this "close-to-real" test-which included the tree and part of the ceiling. Representatives from the Port of Seattle and its maintenance crew, Miller Hull, Woods Bagot, ADI, Armstrong, engineers, and the installation teams attended.

"All key people gathered to see how this would play out in reality, and to put it to the test with their questions," said Chaney. "It was not just a show-and-tell, but a point of assuring the Port of Seattle and the architect they put their trust in the right hands. We were able to address questions and concerns, and the mockup was approved immediately."

The same team that built the mockups did the installation to help facilitate the process. Armstrong shipped most ACGI WOODWORKS panels to size, except for those at the base of the tree, which were field cut and installed once the floor was in place.

PROJECTWORKS Design & Pre-Construction service from Armstrong became involved early and stayed involved throughout. ProjectWorks ensured teams that the design vision could be achieved, helped determine the geometry for triangular panels creating a seamless transition from a round "treetop" to the ceiling perimeter, and solved for potential issues before materials reached the job site. "Hardly anyone wanted to tackle the 'Tree at C.' But we did" shared Travis Styer, Senior Project Manager, Northwest Region, 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." In addition, the architect's desire for a reveal at the ceiling-to-wall transition was solved by creating a perimeter from WOODWORKS ACGI Microperf Linear Closed Series 1 planks, achieving a continuous look.

"This project is a story of one of the biggest strengths of PROJECTWORKS-they worked with standard offerings to create something that suited our needs and met our design vision and performance goals without compromise," said Schreiber. "This level of involvement and problem-solving made all the difference. We received a very comprehensive package, and the shop drawings were fantastic in terms of detail, quality, and intent."

The Result: Marks as high as the Olympic Mountains themselves

After construction started in 2023, the expansion project proceeded smoothly, and the Port of Seattle ceremoniously cut the ribbon on the C Concourse at SEA just ahead of Seattle hosting its first 2026 World Cup match.

"The C Concourse Expansion represents more than a new building for the Port of Seattle-it demonstrates what is possible when innovation, environmental leadership, and partnership come together," said Calkins. "The Port is proud to deliver a transformative space that elevates comfort and connection while advancing its climate goals."

The project was also successful from a budget standpoint. Maintenance crews have convenient plenum access as well as the ability to attend to any impact foot traffic has on the base of the "Tree at C." Perhaps most importantly, every visitor entering the concourse is greeted with warmth and serenity. And, as they continue their journey-which includes unobstructed views of the Olympic Mountains-they are immersed in a sustainable, inspirational experience highlighting the natural beauty, charm, and relaxation of the Pacific Northwest.

"Through close collaboration from concept through construction, we were able to connect all the project's primary features-the ceiling, tree, and grand stair-to tell a meaningful story of the Pacific Northwest," said Schreiber.