ADU rules in Waukesha County, WI — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Waukesha County's zoning code for unincorporated towns has no accessory-dwelling-unit allowance. It bars habitation of trailers/mobile homes outside parks and sets an 1,100 sq ft minimum dwelling floor area, effectively precluding backyard ADUs. Inside cities and villages, check the municipality.
The County Basic Zoning Ordinance (governing consenting unincorporated towns under Wis. Stat. 59.69) contains no ADU or second-dwelling permission. Sec. 3.16(1) prohibits using a trailer or mobile home for human habitation except in an approved mobile-home park. Sec. 3.11(1)(A) requires any single-family building to provide 1,100 sq ft overall floor area. A separate accessory living unit would require a duplex-density lot or a conditional/plan-commission approval. In Waukesha, Brookfield, New Berlin and the villages, zoning is municipal, so ADU rules there are set by the city or village, not the county.
Zoning violations are enforced by the Waukesha County Department of Parks and Land Use; unlawful occupancy or structures may be ordered removed and can carry daily forfeitures under the town's zoning ordinance.
Other ordinances people look up for this city. Green dot = verified primary-source excerpt.
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