Dane County, WI Accessory Structures: Tiny Homes (2026)

Wisconsin treats tiny houses in two tracks. Foundation-built tiny homes under 400 square feet are governed by the Uniform Dwelling Code (Wis. Admin. Code SPS 320-325), which as of the 2020 UDC update adopts IRC Appendix Q for houses 400 sf or less: minimum ceiling height 6 ft 8 in (6 ft 4 in in lofts), minimum room size 70 sf (excluding kitchens), and habitable lofts with alternating tread stairs allowed. Madison (MGO §28.151) permits ADUs on most single-family lots following 2017 Wisconsin Act 67 and Act 317 which preempt local bans on accessory dwelling units; minimum ADU size is typically 300 sq ft. Fitchburg adopted an ADU ordinance in 2022, and Dane County Ch. 10 allows ADUs in agricultural residential districts. Tiny houses on wheels (THOW) are classified as recreational vehicles under Wis. Stat. §340.01(48r) and cannot be used as a permanent dwelling outside a licensed mobile home park or campground. Some Dane County townships (e.g., Springdale, Vermont) have experimented with THOW overlay districts. Utility hookups must meet SPS 382 plumbing and SPS 316 electrical. Septic systems require a Wisconsin Plumbing Permit under SPS 383 if outside a sanitary district.