ADU rules in Waukesha, WI — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
The City of Waukesha regulates accessory dwelling units through Chapter 22 (Zoning) of the Municipal Code, adopted under Wisconsin's local zoning enabling authority at Wis. Stat. Sec. 62.23. Wisconsin has no statewide ADU preemption law, so ADUs are permitted only where Chapter 22 expressly allows them as accessory uses, generally subject to lot size, owner-occupancy, and conditional use review by the Plan Commission. Detached ADUs must also comply with Wisconsin's Uniform Dwelling Code (SPS 320-325) for one- and two-family construction.
Wisconsin cities derive zoning authority from Wis. Stat. Sec. 62.23(7), which empowers the Common Council to regulate the use, height, area, and density of buildings. The City of Waukesha implements this authority through Chapter 22 of the Municipal Code (Zoning), administered by the Department of Community Development. Wisconsin does not preempt local ADU regulation - unlike California or Oregon, there is no statewide statute requiring municipalities to allow ADUs by right - so each city sets its own rules. Construction of an ADU as a one- or two-family dwelling triggers the state Uniform Dwelling Code (UDC) at Wis. Admin. Code Chapters SPS 320-325, which sets minimum construction, energy, and safety standards enforced by certified UDC inspectors. SPS 320.04 contains the definitions used statewide. The City of Waukesha also enforces the State Plumbing Code (SPS 381-387) and State Electrical Code for utility connections to any new dwelling unit. Property owners considering an ADU should contact the Waukesha Zoning Administrator at 262-524-3749 to confirm whether their zoning district permits two-family or accessory dwellings, and whether a conditional use permit is required. Two accessory buildings are generally allowed per lot under Chapter 22, but using one as a dwelling unit is a separate question requiring zoning approval.
Constructing or occupying an ADU without zoning approval and a building permit violates Chapter 22 and Wisconsin's Uniform Dwelling Code. The city may issue stop-work orders, require removal or after-the-fact permitting, and impose forfeitures under the general penalty provisions of the Municipal Code. Unpermitted dwelling units also expose owners to liability under Wis. Stat. Sec. 101.65 for UDC violations.
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Side-by-side rule comparisons with other cities in Waukesha County.
See how other cities in Waukesha County handle adu rules.
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