New Berlin, WI Accessory Structures: ADU Rules (2026)

Chapter 275 of the New Berlin Municipal Code is the city's Zoning Ordinance, adopted by Ordinance No. 2489 on June 17, 2013 under the authority of Wis. Stat. Sec. 62.23. The Definitions article (Sec. 275-9) defines an 'accessory dwelling' as a second dwelling unit integrated with a business on the same lot as the business, expressly excluding mobile homes, recreational vehicles, and travel trailers. This is a narrow definition tied to mixed-use business properties, not a general single-family ADU allowance. Within the residential use regulations and accessory building regulations of Chapter 275, accessory dwelling units and living quarters are not a permitted use within accessory buildings. The city's Accessory Buildings handout from the Department of Community Development confirms that accessory buildings greater than 144 square feet require a zoning permit and may not be used as living quarters. Detached or attached secondary residential units are therefore not allowed by right in standard residential zoning districts (such as the Rs and Rm series). A homeowner who wishes to add a second dwelling unit must pursue a conditional use permit, planned unit development, or rezoning through the Plan Commission and Common Council. In-law arrangements that share kitchen and entry with the principal dwelling and are not separately metered or rentable may not constitute a second dwelling under the Code; verify with the Planning and Zoning Division at (262) 786-8610 ext. 2400 before construction. Wisconsin has no statewide statute mandating that municipalities allow ADUs as of right, so New Berlin's restriction is consistent with Wis. Stat. Sec. 62.23 home rule zoning authority.