Waukesha County, WI Accessory Structures: ADU Rental Restrictions (2026)
Key Facts
- Guesthouses per lot
- 1 maximum
- Rental or lease for occupancy
- Prohibited outright
- Lot size required
- Double the district minimum
- Easement if sold separately (1 family)
- 33 feet wide
- Easement if sold separately (2 families)
- 66 feet wide
Summary
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.
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 permitted unless a single family dwelling is already present on the Lot. Only one (1) Guesthouse per Lot is allowed.
(4) Area requirements: No Guesthouse is allowed unless the Lot upon which the Guesthouse is to be located is at least double the minimum area and lot width requirements of the District. This requirement is intended to prevent the creation of a nonconforming lot in the event that the Guesthouse is sold.
(6) Floor area: The Floor Area of a Guesthouse may be any size. In order to sell a Guesthouse as a separate unit, its Floor Area must conform with the district regulations in which it is located.
Full Breakdown
Sec. 20(1) permits a guesthouse in any district where a single-family dwelling is allowed, but only as an accessory use: Sec. 20(3) requires a single-family dwelling already be present on the lot, and allows only one guesthouse per lot. Sec. " That bars short-term rental platforms and long-term tenants alike, since the ordinance does not distinguish between them. Sec. 20(4) requires the lot to be at least double the district's minimum lot area and width, specifically to prevent creating a nonconforming lot if the guesthouse is later sold off as its own parcel.
Sec. 20(6) leaves the guesthouse's floor area unrestricted for as long as it stays accessory to the main house, but requires it to meet the district's normal floor area rules if it is ever sold as a separate unit. If a guesthouse is sold separately and lacks direct public road access, Sec. 20(7) lets the Plan Commission and County Zoning Agency approve a private easement instead, at least 33 feet wide for one family or 66 feet for two families, provided the easement will not harm the area's development pattern and safely serves emergency and service vehicles.
Violations & Fines
Leasing or renting a guesthouse for human occupancy is a violation of Sec. 3.20(2) and is enforced like any other Basic Zoning Ordinance breach under Sec. 22.03(1): a forfeiture of $50 to $1,000 per offense, with each day the unit remains rented counted as a separate violation, plus prosecution costs and up to six months in jail if unpaid. The Zoning Administrator can also revoke the zoning permit and order the rental use stopped under Sec. 22.02(3)(B).
Frequently Asked Questions
Can I rent my guesthouse out on Airbnb or to a long-term tenant?
How many guesthouses can I build on my property?
How large does my lot need to be to add a guesthouse?
Can I ever sell the guesthouse as its own home?
Sources & Official References
Other rules in Waukesha County
Compare Waukesha County to another location·View the Wisconsin accessory structures overview
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