Accessory Structures in Madison, WI (2026)
4 verified accessory structures rules for Madison, Wisconsin, sourced directly from the municipal code and official government pages.
Verified from official government sources
ADU Rules
Madison lets a zoning lot carry one attached accessory dwelling unit or up to two detached ADUs under Madison General Ordinances § 28.151, so long as the principal building has no more than eight dwelling units total. Detached ADUs, including ones built above a garage, are capped at 25 feet in height, and units inside the main house top out at 1,000 square feet.
Madison Accessory Dwelling Unit Zoning Rules
Some RestrictionsMadison General Ordinances § 28.151
Accessory Dwelling Unit. (a)The principal building shall not contain more than eight (8) dwelling units. (b)No more than one (1) attached accessory dwelling unit or two (2) detached accessory dwelling units may be located on a zoning lot. The detached dwelling units must be in a single structure. A zoning lot may not have both an attached accessory dwelling unit and detached accessory dwelling ...
ADU Impact Fees
Madison doesn't have a separate ADU impact fee: accessory dwelling units are billed under the Multi-Family Park Impact Fee category set by Madison General Ordinances § 20.08(2). Developers owe a Park-Land Impact Fee (734 square feet per unit, or cash in lieu) plus a Park-Infrastructure Impact Fee of $1,032 per unit, indexed annually from a 2016 base.
Madison ADU Park Impact Fees
Some RestrictionsMadison General Ordinances § 20.08(2)(c)2.b, 4, 5.b
2.Park Impact Fee Categories. Park Impact Fees shall be based upon the five following categories of development:a.Single-Family or Duplex... b.Multi-Family. Includes all three-family and multi-family dwelling units with three (3) or fewer bedrooms, as well as accessory dwelling units... Type of Development / Square Feet/Unit or Lodging Room / Multi-Family / 734 ... Type of Development / Fee/Uni...
Shed & Carport Rules
Madison caps the total footprint of sheds and other accessory buildings on residential and mixed-use lots at 1,000 square feet under MGO § 28.131(1)(a), with a conditional use permit needed to go bigger. Height tops out at 15 feet or the principal building's height, whichever is lower, and placement is restricted to specific yard zones with minimum setbacks from property lines.
Madison Shed & Accessory Building Rules
Some RestrictionsMadison General Ordinances § 28.131(1)
(a)Maximum Area Per Lot. Total area of accessory buildings measured at ground floor may not exceed one thousand (1,000) square feet. A larger total building area may be allowed by conditional use approval. The footprint of accessory structures that contain accessory dwelling units shall not be included in the one thousand (1,000) square feet calculation. (b)Maximum Height. The height of the pri...
Tiny Homes
Tiny homes on foundations are allowed in Madison if they meet WI Uniform Dwelling Code and zoning minimum dwelling size. Tiny houses on wheels are treated as RVs and not allowed for permanent residence outside RV parks.
Accessory Structures: Tiny Homes
Some Restrictions2017 Wis. Act 67 (county and municipal conditional use permits)
Conditional use permits. (a) In this subsection: 1. “Conditional use” means a use allowed under a conditional use permit, special exception, or other special zoning permission issued by a county, but does not include a variance. 2. “Substantial evidence” means facts and information, other than merely personal preferences or speculation, directly pertaining to the requirements and conditions an ...
Looking for Dane County county-wide rules?
County ordinances apply to unincorporated areas and may supplement Madison city rules.
Accessory Structures in Dane County →