ADU rules in Janesville, WI — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Janesville zoning is in Chapter 42 of the Code of Ordinances. The current code (adopted 1981) does not provide a separate accessory dwelling unit (ADU) classification; second dwellings are regulated through the underlying residential district standards. The R1 district permits single-family and two-family dwellings, so a duplex on a conforming lot is the typical path for adding a second unit. The City is undertaking a Zoning and Subdivision Code Rewrite (Spring 2024 - Summer 2025) that explicitly studies ADUs, tiny homes, and alternative housing as part of Article 8 (Alternative Development Options).
Authority for municipal zoning is Wis. Stat. Sec. 62.23. Janesville's Chapter 42 (Zoning) sets the residential district list at Sec. 42-440 and zoning map authority at Sec. 42-215. R1 is identified by the City as Single-Family and Two-Family Residence. There is no standalone ADU section in the current code; accessory uses are governed by the Article VI definitions (Sec. 42-122 accessory use) and underlying district standards. Owners proposing a second independent unit on a single-family lot should confirm with the Planning Division whether the lot meets the two-family lot area, frontage, and parking standards of the applicable district, since the current code treats a second unit as a duplex rather than an ADU.
Building or occupying a second dwelling unit without zoning approval is a zoning violation under Chapter 42. The Building Division will not issue a residential building permit for a non-conforming second unit, and the Planning Division can require removal of the unit or restoration to a single-family use.
Janesville, WI
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Janesville, WI
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Janesville, WI
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Janesville, WI
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Janesville, WI
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Janesville, WI
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Side-by-side rule comparisons with other cities in Rock County.
See how other cities in Rock County handle adu rules.
See how Janesville's adu rules rules stack up against other locations.
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