Sauk County, WI Accessory Structures: ADU Rules (2026)

Sauk County's zoning code does not create a general accessory-dwelling-unit category. The closest instrument, Sauk County Code § 7.059, authorizes a temporary secondary dwelling only for a dependency living arrangement, housing someone who needs help with daily living or their caretaker, or for a qualifying farm operation. A property owner must obtain a conditional use approval and a land use permit, and record a notice of temporary permit with the Sauk County Register of Deeds. The unit can be created by converting existing living area, an attic, a basement, or a garage; by adding floor area to the existing dwelling; or by building a detached unit on a lot that already has a dwelling.

Detached units are barred on lots of one acre or less. Size is fixed at not less than 400 square feet and not more than 800 square feet, unless the unit is physically joined to the house through a shared wall or ceiling, and it must sit on the same lot as the owner's dwelling and meet every applicable setback. A private on-site wastewater system must be verified as able to handle the added unit before the permit issues, and mobile homes used as detached units are barred outright in SFR and MFR districts.

For a farm-based unit, the farm's gross income must exceed $6,000.00 a year or $18,000.00 over three years, and up to two such units per farm may be approved for parents, children, or hired workers deriving at least half their income from the operation.