Milwaukee, WI Accessory Structures: ADU Rules (2026)

Milwaukee Code of Ordinances Chapter 295 (Zoning) classifies accessory dwelling units as a limited use in residential districts under Table 295-503-1. Section 295-503-2-f caps a parcel at one ADU and, for an internal or attached unit, requires at least one owner of the existing principal dwelling to occupy it as a primary residence at the time of the building permit application (verified by two forms of documentation such as a driver's license, voter registration or utility bill). 5 then sets design standards by ADU type: minimum floor area of 300 square feet for all three types (internal, attached, detached); maximum floor area of 1,000 square feet for internal/attached units (capped at the size of the largest unit on the parcel) and 1,300 square feet for detached units; a detached ADU cannot exceed the height of the principal building and must sit at least 3 feet from the side lot line, with a minimum 10-foot front-to-back and 5-foot side-to-side separation from the principal building. Fail any of the use standards and the ADU becomes a prohibited use, not merely a special-use candidate.