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Sea-Tac Airport’s New Concourse D Annex Will Improve the Passenger Experience

Sea-Tac Airport Rendering Exterior

The HOK-designed building evokes the Pacific Northwest and the joy of flight, and is expected to become the first airport terminal building in the United States to achieve Silver certification through the USGBC’s LEED v4 for Building Design and Construction.

The new two-story Annex to Concourse D has opened at the north end of Seattle-Tacoma International Airport’s main terminal. An integrated design-build team including the Port of Seattle; HOK as lead architect, landscape architect, interior designer and sustainability coordinator; and The Walsh Group as design-builder developed the Annex to relieve congestion and improve the experience of passengers during peak periods.

The 32,400-sq.-ft. building adds six new passenger holdroom gates, multiple concession stands, free Wi-Fi, electric charging stations and a children’s play area. From the Annex, passengers board buses that take them to their planes on the tarmac, reducing the time spent waiting for aircraft to arrive at a gate.

“Though it serves hardstand operations, it looks and functions like a traditional terminal,” said Lance Lyttle, managing director at Sea-Tac Airport. “In fact, it rivals or exceeds the offerings in some of the airport’s other holdroom areas.”

As one of the first airport buildings seen as travelers approach the airfield, the Annex needed to be welcoming and aesthetically pleasing while enhancing the passenger experience.

“The elegant, beautiful form of this simple building evokes the joy of flight,” said Alan Bright, FAIA, LEED AP BD+C, a senior design principal with HOK. “One of our inspirations for the design was the majestic great blue heron—one of the most recognizable birds in the state of Washington. The design creates a beautiful, daylit open pavilion with an expressed structure. Integrating natural materials from the local landscape provides a calming, enjoyable experience for travelers and the people who work here.”

The building’s all-glass curtain wall brings in natural light and connects passengers to the outdoor environment. Using a light color palette for the interiors contributes to the open, comfortable feeling. The distinctive glue-laminated (glulam) timber truss system constructed from locally sourced Douglas fir trees adds to the Pacific Northwest aesthetic and significantly reduces the building’s embodied carbon. A glass art installation with blown-glass pieces representing spring, summer, winter and fall soon will be suspended from the pavilion’s ceiling in four prominent locations.

“The natural splendor of the Pacific Northwest inspired our design of a contemporary facility that helps passengers get what they need, relax and experience the beauty of the region,” added Todd Buchanan, AIA, LEED AP BD+C, project manager and practice leader for HOK’s Seattle studio. “The Port of Seattle is a great client that created an environment of trust and collaboration among all team members. This teamwork enabled us to design and build the Annex within the tight budget and in just 18 months.”

As they cross a skybridge from the main level of Concourse D and descend into the ground-level Annex space where they will board the buses, passengers traverse a gently sloped walkway that appears to float over the space and offers clear views of all six gates. This meandering walkway, which runs north and south parallel to Sea-Tac’s main departures road, defines the slope of the open pavilion’s long-span roof.

Positioning the 12 COBUS shuttle vehicles on the perimeter of the concourse allows for more intuitive wayfinding and for an equal distribution of lounges. A new airfield drop-off area gives arriving passengers direct access into the main terminal.

The Port of Seattle wanted the new facility to provide passengers and employees with a healthy, sustainable environment. The Annex is expected to become the first airport terminal building in the United States to achieve Silver certification through the USGBC’s LEED v4 for Building Design and Construction green building rating system. In addition to the extensive daylighting, sustainable design strategies include use of locally sourced materials; highly reflective roofing materials that decrease the heat island effect; a rainwater management system that recycles water runoff from the sloped roof to irrigate the native landscaping; and air curtains and a radiant floor heating system that reduce energy use and help maintain a comfortable indoor temperature. The team recycled 95 percent of the construction waste. By relieving congestion at the airport, the new Concourse D Annex reduces fuel use by airlines and saves greenhouse gas emissions.

HOK’s design team used virtual reality tools to explore design concepts for the Annex with the Port of Seattle. “Our use of VR allowed them to experience the space before it was built and helped us meet the accelerated schedule,” said Buchanan.

In addition to HOK and The Walsh Group, the project’s design-build team included Lund Opsahl LLC, Osborn Consulting, Inc., Hart Crowser, Casne Engineering and Notkin Mechanical Engineers.

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