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 dwellin...
ADU Impact Fees
Madison prices an accessory dwelling unit at the Multi-Family park impact fee rate, not the higher Single-Family rate. The Park-Infrastructure Impact Fee is $1,032 per unit in 2016 dollars, indexed every January 1, and the Park-Land Impact Fee is built on 734 square feet of land per unit. Both are collected when the Chapter 29 building permit issues.
Madison Park Impact Fees on Accessory Dwelling Units
Some RestrictionsMadison General Ordinances § 20.08(2)(c)2.b, 4, 5.b, (d)3
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 Single-Family/Duplex 1,081 Multi-Family 734 ... Park-Land Impact Fee . The Park-Land Impact Fee shall be the product of the above-noted land dedication requirement, less any land dedications or cr...
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. (Am. by ORD-25-00068 , 10-16-25) (b) M...
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 →