It’s distinctive blue, shimmering coating is visible to millions from the nearby Highway 101, but now the Marin Civic Center — architect Frank Lloyd Wright’s largest completed public project — is getting a new roof.

“This is going to be a widespread and visible project that will encompass the entire expanse of the Civic Center. Just the removal of the existing roof alone will be a significant undertaking,” said Patrick Zuroske, Marin County Department of Public Works (DPW) Capital Projects Division manager.

The 50-year-old building is listed in the National Register of Historic Places. The original cost to construct all the phases of the center was about $14.6 million, not adjusted for inflation, said county officials.

Cost to replace the distinctive roof is estimated at $21.2 million.

The roof has been repaired several times over the years including in 2015 after a portion of the interior ceiling collapsed when rain water collected in roof membranes.

The county of Marin has agreed to pay Wiss Janney Elstner Associates, Inc. (WJE) to design and manage the project to redo the 220,000-square-foot concrete roof.

The first phase of the construction project is scheduled to begin during summer 2017 on the shorter Administration Wing and the library dome on the building’s southern end. Summer 2018 should see the start of the second phase, focused on the longer Hall of Justice at the northern end. The third and final phase will take place in 2019 and address the skylight refurbishment.