5 county-level rules, plus city-specific rules for 3 cities in Waukesha County, Wisconsin.
Verified from official government sources
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.
Waukesha County Basic Zoning Ordinance Sec. 3.16(1)
Except within an approved Mobile Home Park or camp, no trailer or Mobile Home shall be used for the purpose of human habitation.
In unincorporated Waukesha County towns, a lot is limited to two accessory buildings and a total footprint of 600 sq ft (lots under 14,000 sq ft) or 750 sq ft / 2% of lot area on larger lots. One detached shed under 200 sq ft may sit 5 ft from
Waukesha County Basic Zoning Ordinance Sec. 3.09(3)(A)4
One detached accessory Building on any Lot which is less than two hundred (200) square feet in area may be located five (5) feet to the Side Lot Line unless otherwise excepted under any other provision.
The county's town zoning code has no dedicated garage-conversion rule. Converting a garage to living space must meet the 1,100 sq ft minimum dwelling floor area and any state building-code and septic/well approvals, and cannot create a second dwelling unit. Cities and villages regulate conversions themselves.
A carport is treated as an accessory structure under county town zoning. It counts toward the two-building limit and the accessory-building footprint cap (600 sq ft on lots under 14,000 sq ft), must meet district side-lot offsets, and sit at least 10 ft from the house. Cities and villages set
Waukesha County Basic Zoning Ordinance Sec. 3.09(5)
No detached Accessory Building shall be erected, structurally altered or placed or a Lot so that any roofed or enclosed portion thereof is closer than ten (10) feet to the Principal Building on said Lot.
Waukesha County town zoning effectively blocks most tiny homes: any single-family dwelling must have 1,100 sq ft overall floor area (850 sq ft on the first floor), and tiny-house-on-wheels living is barred outside approved mobile-home parks. Cities and villages set their own dwelling-size rules.
Waukesha County Basic Zoning Ordinance Sec. 3.11(1)(A)
Any Building intended in whole or part for single-family residential purposes shall provide a minimum overall Floor Area of eleven hundred (1,100) square feet with at least eight hundred fifty (850) square feet of Floor Area on the first floor.
3 cities in Waukesha County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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