In five years, Seattle-Tacoma International Airport became the fastest-growing large-hub airport in the U.S., with annual passenger traffic rising to 46.9 million in 2017 from 33.2 million in 2012. The Port of Seattle’s 32,400-sq-ft Concourse D annex was designed to meet that surge in passenger traffic.

The project created new space to reduce congestion at crowded gates, allowing waiting aircraft to load and unload passengers more quickly and cut passenger wait times. As a result, fuel usage and greenhouse gas emissions from idling aircraft were reduced.

The annex includes room for six hold-room gates and “hardstand operations,” where passengers deplane onto the ground and board a shuttle bus that takes them to an annex drop-off area connected directly to the terminal.

The annex also houses multiple concession stands, electric-charging stations and a children’s play area. Built using integrated design-build, it is expected to be North America’s first airport terminal to achieve LEED v4 Silver certification. Sustainable highlights include locally sourced materials, highly reflective roofing materials and extensive daylighting.

Unforeseen conditions included an electrical duct bank, discovered during early potholing, that required designers to revise the building foundation to bridge the duct bank while maintaining the construction schedule. Building information modeling helped to define the annex’s form and space and verify its cost and energy performance.

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