Accessory Structures in Dane County, WI (2026)

5 county-level rules, plus city-specific rules for 4 cities in Dane County, Wisconsin.

Verified from official government sources

Note: These county rules apply to unincorporated areas of Dane County. If you live within an incorporated city, that city's own rules apply — see the city list below.

ADU Rules

ADUs in unincorporated Dane County are permitted in appropriate zoning districts under Chapter 10. ADUs must be accessory to the principal dwelling and cannot be sold separately.

Dane County ADU / Accessory Dwelling Rules

Some Restrictions

Dane County Code of Ordinances, ch. 10.103(1)(c)-(k) (Accessory dwelling units)

(c) A detached accessory dwelling unit may be included in either an existing or new dwelling unit. (d) Lots accommodating an accessory dwelling unit must meet the minimum lot size for the applicable zoning district. (e) In no case shall an accessory dwelling unit exceed 800 square feet of occupiable floor area. (f) No accessory dwelling unit shall have more than two bedrooms. (g) Accessory dwel...

Full ordinance details →Official source ↗

Shed Rules

Sheds and accessory structures in unincorporated Dane County require a building permit and must comply with Chapter 10 setback requirements for the zoning district.

Dane County Shed & Outbuilding Rules

Some Restrictions

Full ordinance details →Official source ↗

Garage Conversions

Garage conversions to living space in unincorporated Dane County require building permits and must meet habitable space standards under Wisconsin building code. Converting to an ADU is permitted in appropriate zoning districts.

Dane County Garage Conversion Rules

Some Restrictions

Full ordinance details →Official source ↗

Carport Rules

Carports are regulated as accessory structures under Madison MGO Ch. 28 (Zoning) and the Wisconsin UDC (SPS 321). A building permit is required for any carport in Madison, Fitchburg, Middleton, Verona, Sun Prairie, and Stoughton. Dane County Ch. 10 Zoning governs unincorporated carports.

accessory-structures/carport-rules

Some Restrictions

Full ordinance details →Official source ↗

Tiny Homes

Foundation-built tiny homes in Dane County are treated as standard dwellings under Wis. Admin. Code SPS 320-325 (UDC). Tiny homes on wheels are classified as RVs/mobile homes under Wis. Stat. §101.91. 2017 Wisconsin Act 67 and Act 317 expanded ADU flexibility. Minimum habitable size is generally 150 sq ft under IRC Appendix Q.