Accessory Structures in Waukesha County, WI (2026)
4 county-level rules, plus city-specific rules for 1 city in Waukesha County, Wisconsin.
Verified from official government sources
ADU Rules
Unincorporated Waukesha County towns allow an in-law unit as a conditional use in Residential, Agricultural, B-1 and B-2 districts, but it is capped at 1,000 square feet and two bedrooms, needs Plan Commission and County Zoning Agency approval, and requires a recorded deed restriction limiting who can live there.
In-Law Unit Rules in Waukesha County Towns
Significant RestrictionsWaukesha County Basic Zoning Ordinance Sec. 3.08(7)(Z)
(Z) In-Law Unit: In any Residential, Agricultural, B 1 or B 2 zoning district, except FLC, subject to the following... 1. The location, building plan, and site plan and plan of operation shall be submitted to and approved by the Plan Commission and the County Zoning Agency. ... 3. Maximum living area of the In-law Unit shall not exceed one thousand (1,000) square feet and shall contain no more ...
ADU Rental Restrictions
A guesthouse in unincorporated Waukesha County can never be leased or rented for human occupancy: Sec. 3.20 limits it to occasional occupancy by the homeowner's guests, caps it at one per lot, and requires the lot be double the district's normal minimum size.
Guesthouse Rental Ban in Waukesha County
Heavy RestrictionsWaukesha County Basic Zoning Ordinance Sec. 3.20(1)-(4), (6)
3.20 Guesthouses. (1) Use permitted: Guesthouses, as defined by this Ordinance, are permitted in any District in which a single family dwelling is permitted. (2) Permanent habitation prohibited: A Guesthouse must be used only for occasional occupancy by guests of the owner and shall not be leased or rented for human occupancy. (3) Accessory to a single-family dwelling: No Guesthouse is permitte...
Shed & Carport Rules
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
Shed and Accessory Building Rules in Unincorporated Towns
Some RestrictionsWaukesha 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.
Tiny Homes
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.
Tiny Homes and Minimum Dwelling Size in Town Zoning
Some RestrictionsWaukesha 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.
Accessory Structures by City in Waukesha County
1 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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