Des Moines International Airport is preparing to construct a new terminal to replace its existing building in a phased project estimated to cost as much as $769.8 million.

The airport is the largest in Iowa. Its current 12-gate terminal building dates to 1948, and with the airport projecting demand for 17 gates by 2032 and 19 by 2042, airport leaders say it has reached the end of its useful life. The plan calls for a three-phase project to break up costs and allow the first phase of work to fit current available funding while still addressing increased capacity needs.

The airport has been working with Anser Advisory LLC to act as the owner’s representative on the project. In April, the Des Moines Airport Authority board of directors awarded a design services contract to Kansas City, Mo.-based HNTB Corp. Seven firms submitted for the job, and design firms Corgan and Fentress Architects were also interviewed, airport authority records show. HNTB had previously worked with the airport on a planning study for the new terminal.

Tom Rossbach, HNTB’s aviation architecture senior director and project manager for the Des Moines airport contract, said in a statement that he expects the design “will be transformational in terms of passenger experience, efficiency and flexibility.”

The airport issued an RFQ for a construction manager at-risk in April and has since interviewed three firms. Kayla Kovarna, a spokesperson for the airport, says the board is scheduled to select the construction manager at their Aug. 9 meeting.

That first phase would include the construction of a new terminal with five gates, plus a central energy plant, offices and a pedestrian bridge to the parking garage. It would also include additional airside and landside infrastructure improvements, for a total estimated cost of $411.4 million.

The plans then call for a northward expansion adding four gates to the concourse at an estimated cost of $87.8 million, and a southward expansion adding eight gates. That final phase would also include demolition of the current terminal, with a total cost estimated at $233.9 million.

Work is not expected to break ground until 2024 at the earliest, Kovarna says. If it does, planning documents indicate the first portion could be completed in 2026 and all three phases by early 2030.

The airport has also developed a concept for another possible phase of work to further expand the terminal concourse up to 22 gates as its ultimate buildout.