The lakefront museum plans to add 17,000 square feet and a new entrance, to the east. Construction should begin in fall and take one year.
In addition to expanding the Milwaukee Art Museum will make structural repairs, including to the leaky roof and windows as well as to foundation weaknesses.
The estimated cost of the repairs and expansion is $25 million, with Milwaukee County paying $10 million and the museum raising the rest.
According to planners, the addition will enable the art museum to display thousands of art works that have been in storage, because of a shortage of space.
The addition will not affect the adjacent Calatrava building, which opened in 2001.