Madison, WI Accessory Structures: Shed & Carport Rules (2026)

Madison General Ordinances § 28.131 governs every accessory building or structure, sheds, detached garages, workshops, greenhouses, on a lot used exclusively for residential or mixed-use purposes. Total ground-floor area of all accessory buildings on the lot cannot exceed 1,000 square feet; the only way past that cap is a conditional use approval. Height is limited to 15 feet or the height of the principal building, whichever is lower, though carriage houses within a historic district may match the height of the original historic structure, and accessory dwelling units are instead governed by the underlying district's height limit.

Placement is tightly zoned. A shed can sit inside the building envelope, or in a rear yard at least 3 feet from any property line, or in a side yard at least 3 feet from the line if it sits behind the rear plane of the principal building. On a corner lot, an accessory building placed in the side or rear yard along the street side must hold the same setback required of a principal building in that zoning district. Reversed corner lots get an extra rule: no closer to the street side lot line than the front yard setback of the neighboring property for the first 25 feet from the shared line. Sheds and garages must also sit at least 3 feet from the principal building and from any other accessory structure on the lot.

Two abutting owners may share a single detached garage built across the lot line, provided a joint driveway and a recorded joint access-and-maintenance agreement are in place. A garage in a side or rear yard that is demolished can be rebuilt within the existing setback within one year, capped at 24 feet in length or width and no more than 2 feet taller, longer, or wider than what came down.