ADU laws in Michigan

In plain words

Michigan has no statewide law about accessory dwelling units (ADUs). An ADU is a small second home on the same lot as a house. It can be inside the house, attached to it, or in a separate backyard building. In Michigan, cities, villages, townships and counties write their own zoning. Zoning is the local rulebook for what can be built where. The state zoning law gives towns that power, but it says nothing about ADUs today. So each community decides.

Rules vary a lot. Ann Arbor allows ADUs in many zones with a building permit and no public hearing. Grand Rapids allows them on single- and two-family lots, within size and placement limits. Detroit planners proposed allowing ADUs in more zones, but the City Council had not adopted it as of the city's latest update.

A state bill is pending. House Bill 5585 would make small ADUs 'by right' across Michigan. By right means staff must approve an ADU that meets the listed rules, with no public hearing. It covers ADUs up to 800 square feet or 75% of the house, whichever is smaller. They must sit at least 5 feet from side and rear lines. That distance is called a setback. Towns could not demand parking or owner occupancy, which is a rule that the owner must live on the property. The bill had a hearing in May 2026 but no vote yet.

For now, your local code is what counts. You may be able to build an ADU if local rules and your property allow it.

The rules at a glance

What to do next

1. Find out which government zones your land: your city or village if you live inside one, otherwise your township (or, in some areas, the county).
2. Ask the zoning office whether ADUs (also called accessory apartments, granny flats or carriage houses) are permitted in your district, need a special land use approval with a hearing, or are not allowed.
3. Get the local limits in writing before you design: size, height, setbacks, parking, owner occupancy, rental rules and utility connections.
4. If you are not on public sewer and water, ask your local health department about well and septic capacity for a second unit.
5. Check HOA covenants and deed restrictions, which zoning approval does not override.
6. Follow HB 5585 and HB 6082-6085 on legislature.mi.gov; bills not passed by the end of the 2025-2026 session must be reintroduced in 2027.

Grants, loans and tax breaks

• MSHDA Housing Readiness Incentive Grant: Grants of up to $50,000 to cities, counties, townships and villages to adopt zoning text amendments, master plan updates and similar changes that increase housing supply. MSHDA's Housing Ready toolkit lists allowing ADUs in all residential zones as a recommended reform. This money goes to local governments, not homeowners; MSHDA reported limited funding left as of September 16, 2026. Program page

What your town still decides

Counties, townships, cities and villages write their own zoning under the Michigan Zoning Enabling Act (2006 PA 110, MCL 125.3101 and following). The act gives them the power to zone but has no ADU provision: its definitions section (MCL 125.3102) has no ADU term, and HB 5585 would add the first one as new text. The legislature's full-text bill search finds 'accessory dwelling' only in 2026 bills, none enacted, and in no bill from 2019 through 2024. So each community decides whether ADUs are allowed, whether they need a special land use permit and public hearing, and what limits apply. Rules range from staff-level approval with no public hearing (Ann Arbor) and an application with a site plan and neighborhood-outreach summary (Grand Rapids) to codes that do not allow ADUs in most neighborhoods (Detroit, where a reform is proposed). Local government groups, including the Michigan Municipal League and the Michigan Townships Association, describe the 2026 House zoning package as state preemption of local zoning, and the League urged members to act against it. The state housing agency (MSHDA) instead uses grants to encourage local zoning changes, and its Housing Ready toolkit recommends allowing ADUs in all residential zones.

Examples of local rules

• Grand Rapids: Allows one ADU on single- and two-family lots, attached or in a separate building. Maximum size is 850 sq ft and no more than 40% of the house. Detached ADUs must sit behind the house, at least 6 ft from it and 3 ft from side and rear lot lines, and are capped at 20 ft tall (25 ft if they meet main-house setbacks). Applications need a site plan, elevations and a summary of neighborhood outreach. Leased ADUs must be registered as rentals, cannot be rented for under 30 days, and a deed restriction bars selling the ADU separately. The city's April 2025 FAQ lists no owner-occupancy rule. Source
• Ann Arbor: Changes adopted in 2021 allow ADUs in more zoning districts and allow newly built detached ADUs (before, they had to be in existing buildings). Approval is administrative: a building permit is needed, but no site plan, public hearing or neighbor notice. The city page I checked mentions no owner-occupancy rule; check the September 2023 ADU guidebook for size and occupancy details. Source
• Detroit: Detroit's current code does not broadly allow ADUs. The 'Let's Build More Housing' zoning ordinance would allow ADUs (carriage houses) in R2 through R6 districts without special permission. It went to a City Planning Commission hearing on October 2, 2025; the city said Council would not vote in 2025 but might take it up in 2026. We found no record of adoption. Source

What we’re still confirming

• HB 5585, which would make ADUs a permitted use statewide, hasn't had a committee vote, and the session ends in December 2026.
• Ask Grand Rapids whether an ADU needs a public hearing or only staff review, and confirm that it no longer requires the owner to live on site.

Laws, bills and citations

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.