ADU rules in Washtenaw County, MI β also called accessory dwelling unit regulations or granny flat ordinances β cover setbacks, owner-occupancy, parking, and permit requirements.
Washtenaw County does NOT regulate accessory dwelling units. Under the Michigan Zoning Enabling Act (PA 110 of 2006, MCL 125.3101 et seq.), zoning authority sits exclusively with home-rule cities, charter townships, and general-law townships. Each Washtenaw County jurisdiction sets its own ADU rules. The City of Ann Arbor has one of the most permissive ADU ordinances in the state, codified in UDC Section 5.16.6, allowing detached, attached, and internal ADUs in R1-R4 zoning districts on lots with a single-family home. Other municipalities β Ypsilanti, Pittsfield Charter Township, Saline, Chelsea, Dexter, Scio Township, Ann Arbor Charter Township β have separate rules.
Michigan's land-use framework gives general zoning authority to cities, villages, and townships under the Michigan Zoning Enabling Act, codified at MCL 125.3101 through 125.3702 (Public Act 110 of 2006). MCL 125.3201 authorizes local legislative bodies to enact zoning ordinances regulating land use and development. Counties may zone only in unincorporated, unzoned territory, and once a township adopts its own zoning ordinance the township ordinance controls (MCL 125.3209). Washtenaw County is fully covered by city and township zoning, so there is no county ADU rule. Michigan has no statewide ADU statute comparable to California's SB 9/SB 13 framework β bills such as HB 4221 of 2021 have been considered but none have passed into general preemption. Ann Arbor leads the county on ADUs: UDC Section 5.16.6 permits detached, attached, and internal ADUs in R1, R2A, R2B, R3, R4A-E districts where the lot has a single-family home, with size limits typically 600 sq ft on smaller lots and 800 sq ft on larger lots (or matching the main dwelling's ground floor area, whichever is smaller), minimum 3-foot setbacks for detached ADUs, and combined occupancy capped at four unrelated persons plus offspring. Critically, Ann Arbor expressly prohibits short-term rental of an ADU. Other Washtenaw jurisdictions vary considerably β Ann Arbor Charter Township amended its accessory structure ordinance in 2024, and Pittsfield, Ypsilanti Township, and Scio Township each maintain distinct rules. Building construction must comply with the Stille-DeRossett-Hale Single State Construction Code Act (PA 230 of 1972, MCL 125.1501) and the Michigan Residential Code regardless of zoning.
No county-level ADU enforcement. Violations are pursued by the local city or township under its zoning ordinance, typically as a municipal civil infraction with daily fines, plus stop-work orders and orders to remove unpermitted structures. Building Code violations under PA 230 of 1972 are enforced locally per MCL 125.1521. Unpermitted electrical or plumbing work under the Skilled Trades Regulation Act (PA 407 of 2016) is independently enforceable by LARA. Renting an ADU as a short-term rental in Ann Arbor is a separate violation under Chapter 97 of the Ann Arbor Code.
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