Wauwatosa, WI Accessory Structures: ADU Rules (2026)

10 of the zoning ordinance to let homeowners add housing while keeping neighborhood character intact. 075 lets an owner create an ADU by converting interior space such as an attic or basement, adding floor area to the existing house, building a detached unit, converting an existing accessory building, or building a new principal house with an internal or detached ADU. Only lots with a detached house, semi-detached house, attached house, or two-unit house qualify, and only one ADU is allowed per lot. Size is capped at 1,000 square feet or the gross floor area of the principal dwelling, excluding an attached garage, whichever is less; garages, low basements under seven feet, and areas under five feet of ceiling height don't count toward that floor area.

A detached ADU built after June 19, 2019 must match the principal house's exterior finish and roof pitch, keep a minimum five-foot separation from the principal dwelling free of any structure taller than thirty inches, and sit behind the front of the principal dwelling rather than in front of it. Height is capped at sixteen feet, rising to twenty-four feet if the unit sits above a garage; the Zoning Administrator may approve a single-story detached ADU up to twenty feet if its roof pitch matches the main house.

In every case the ADU cannot be taller than the principal dwelling. No additional off-street parking is required beyond what the principal dwelling already needed, and lot coverage maximums don't apply to a detached ADU. Before construction the chief building official must review and approve plans for compliance with the building and life-safety codes. The section was adopted by Ord. O-19-11 pt. II on June 18, 2019, and amended by Ord. O-22-24 pt. I on September 20, 2022.