The Port of Seattle Commission authorized $1.1 billion on August 11, 2026 to advance the S Concourse Evolution, a renovation of Seattle-Tacoma International Airport’s 1973-built international concourse now estimated at $2.5 billion, up from roughly $900 million when the project was first budgeted in 2023. Hensel Phelps, selected as general contractor in 2023, is already soliciting subcontractor bid packages. Major construction starts in 2027, with substantial completion targeted for 2034.

What the Vote Actually Unlocks

Tuesday’s authorization does not start construction on its own. It funds the S Concourse Evolution program through 2029, with the remaining balance of the $2.5 billion estimate scheduled to come back to commissioners for approval later. The Port has been explicit that the money comes from the Airport Development Fund and future revenue bonds, not tax dollars, which matters for a program this large because it means airline landing fees, concession revenue, and future bond issuance carry the exposure if costs move again.

The scope itself is a restructuring job as much as an expansion. The existing S Concourse, originally opened in 1973 as the South Satellite and last substantially altered in 1984, is a seven-level, 350,000-square-foot building. The Evolution adds roughly 150,000 square feet on top of that, including a new upper concourse level and dual-level boarding at select gates, without adding to the concourse’s 12-gate count. Port officials have said the priority is seismic and structural work meant to keep the building in service for another 50 years, with the passenger-facing upgrades — expanded dining, retail, and lounge space — layered on top. The commission is targeting LEED Silver certification, with a projected 58% cut in annual greenhouse gas emissions and a 16% reduction in energy use against the Port’s own standard, achieved partly through high-performance glazing and all-electric building systems.

Gate closures will come in waves rather than all at once: three of the concourse’s 12 gates are expected to be down at a time, with a temporary ground-boarding annex built nearby to keep departures moving through construction.

A Team That Predates the Funding Vote — and a Budget That Has Moved

None of the coverage of Tuesday’s vote named who is actually building the project, which is unusual for a program this size. The Port selected Hensel Phelps Construction Co. as general contractor and construction manager back in August 2023, issuing a notice of intent to award after Hensel Phelps beat out Hoffman Skanska Joint Venture, PCL Construction Services, and Turner Walsh Partners in a shortlisting process run under Washington’s GC/CM statute, RCW 39.10. AECOM was brought on the same year to lead program management, executing a $35 million contract in July to steer design, working alongside HOK as design partner. As of this month, that team is still active: a subcontractor solicitation for SCE bid package 02 was open with an August 28, 2026 response deadline, confirming work is proceeding on the ground well ahead of the funding vote making headlines.

What has changed since 2023 is the number attached to the job. When Hensel Phelps was first selected, the project carried a preconstruction contract of roughly $8 million against a maximum allowable construction cost of $900 million, with the total program then estimated around $1.5 billion. The $2.5 billion figure the Port cited on August 11 is nearly triple that original construction-cost figure and roughly two-thirds higher than the total program estimate reported when the contractor was picked. The Port has not published a line-item explanation for the increase, and it is a gap worth flagging rather than glossing over: escalation of this scale over three years, on a project that has not yet reached major construction, is the kind of detail regional aviation reporting has largely left unexamined in favor of the headline authorization figure.

Where This Fits in Sea-Tac’s Longer Construction Queue

S Concourse Evolution is the last of the airport’s legacy-concourse overhauls to reach construction under the $5.5 billion Upgrade SEA program, which the Port launched in 2023 to modernize facilities built decades ago for a fraction of today’s passenger volume. The N Concourse modernization finished in 2021, the International Arrivals Facility opened in 2022, and this year alone has seen the completion of both the SEA Gateway ticketing overhaul and the C Concourse Expansion, which added four floors between Concourses C and D for a final budget of $399 million.

The comparison with C Concourse is instructive on cost. That project added roughly 145,000 square feet, taking the building from 81,000 to 226,530 square feet, for $399 million — call it around $2,750 per added square foot. S Concourse Evolution adds a similar 150,000 square feet for $2.5 billion, or over $16,000 per added square foot. The gap is the point: unlike C Concourse, which was largely new construction stacked on an existing base, S Concourse Evolution is a full seismic and systems overhaul of an aging 350,000-square-foot building with the addition layered in, not a simple expansion. It is a more useful yardstick for what SEA’s next major project, the $2.2 billion second terminal now in environmental review, might eventually cost once construction pricing is attached to it.

Nationally, the number puts S Concourse Evolution in the same range as Portland International’s $2.15 billion main terminal rebuild, which opened its core terminal in 2024 and is finishing secondary nodes now — a reminder that big-airport renovations in the Pacific Northwest are currently running well above $2 billion regardless of which facility is being rebuilt.

Open Questions Ahead of 2027

Two things remain unresolved. First, the remaining roughly $1.4 billion of the $2.5 billion estimate still needs commission approval, and the Port has not set a date for that vote. Second, the completion timeline has shifted: reporting from 2023 described a two-phase construction sequence running from 2029 to 2031, while the Port’s August 2026 announcement now points to major construction beginning in 2027 and substantial completion in 2034. Neither the Port nor Hensel Phelps has publicly reconciled the two schedules, and it is not yet clear whether the extended timeline reflects the larger scope, the seismic retrofit work, or simply a more conservative estimate now that design is further along.

Project Fact Sheet

• Project Name: S Concourse Evolution (SCE)
• Location: Seattle-Tacoma International Airport, SeaTac, Washington, USA
• Project Value: $2.5 billion total estimate; $1.1 billion authorized August 11, 2026 (Port of Seattle)
• Client/Owner: Port of Seattle
• Main Contractor: Hensel Phelps Construction Co. (general contractor/construction manager)
• Key Components: Restructuring of an existing seven-level, 350,000-sq-ft concourse; approximately 150,000 sq ft of new space; new upper concourse level; dual-level boarding at select gates
• Procurement Model: General Contractor/Construction Manager (GC/CM) under RCW 39.10
• Funding Source: Port of Seattle Airport Development Fund and future revenue bonds; no taxpayer funding
• Construction Start: Early works fourth quarter 2026; major construction 2027
• Expected Completion: 2034 (substantial completion)
• Environmental Features: Targeting LEED Silver certification; projected 58% cut in annual greenhouse gas emissions and 16% reduction in energy use versus Port standard

Project Team

• Owner: Port of Seattle
• General Contractor/Construction Manager: Hensel Phelps Construction Co.
• Program Manager: AECOM
• Design Partner: HOK
• Port of Seattle Commission President: Ryan Calkins
• SEA Airport Managing Director: Wendy Reiter