ADU Rules: Milwaukee vs West Allis

Milwaukee allows 1 ADU per lot with a single- or two-family home under MCO Chapter 295. Owner-occupancy required for the principal unit. Detached ADU: min 1.5 ft side, 4 ft rear setbacks.

West Allis regulates accessory buildings under Chapter 19 (Zoning) of the Revised Municipal Code, adopted under the city zoning authority of Wis. Stat. Sec. 62.23. Sec. 19.42 (Residential Accessory Buildings) caps detached accessory structures at 50% of the principal building area, not to exceed 800 square feet, with a maximum exterior wall height of 20 feet. Setback minimums include 10 feet from the principal building, 3 feet from side lot lines, and 3-5 feet from rear lot lines depending on alley adjacency. The West Allis Zoning Code does not establish a separate by-right accessory dwelling unit (ADU) class in the manner of cities like Appleton; a habitable second dwelling unit on a single-family lot generally requires zoning interpretation by the Planning and Zoning Department.