Building an ADU in Michigan

Michigan has no statewide ADU law

No Michigan law makes local governments allow ADUs. Your city, village, township or county zoning ordinance decides whether you can add a backyard cottage, garage apartment or basement unit, and on what terms.

The Michigan Zoning Enabling Act lets a local unit of government regulate land development through a zoning ordinance and adopt rules "designating or limiting the location, height, bulk, number of stories, uses, and size of dwellings, buildings, and structures." Those general zoning powers are where local ADU rules come from.

The Act also lets a local ordinance list "special land uses" that need review and approval. For a discretionary special land use, owners and occupants within 300 feet get notice and can ask for a public hearing. If your community treats an ADU as a special land use, expect that extra step.

Start with your local planning or zoning office. Outside cities and villages, zoning is done by the township, or by the county where the township has no zoning ordinance of its own. [1][2][4][5]

The pending ADU bill: HB 5585

HB 5585, sponsored by Rep. Luke Meerman, would amend the Michigan Zoning Enabling Act. It was introduced and referred to the House Committee on Government Operations on February 24, 2026. As of October 10, 2026, the bill's history shows no committee vote, only cosponsor changes (the last on May 14, 2026). It is not law.

As introduced, HB 5585 would make an ADU a permitted use, approved only "on a nondiscretionary basis by administrative staff and without a public hearing," if:

• it is no larger than 800 sq ft or 75% of the home's gross square footage, whichever is less;
• the ADU and the home are set back at least 5 feet from the rear and side property lines;
• it is in a district where residential use is permitted; and
• it is inside, attached to, or on the same parcel as a single-family home that exists or is under construction.

The bill would also:

• leave ADUs out of density limits;
• bar parking and owner-occupancy requirements for ADUs;
• bar design, height or placement rules stricter than those for the main home;
• bar rules that forbid or require a basement;
• let local governments approve an ADU that was built without approval.

Local ordinances could still be more permissive. The bill would take effect 180 days after it is enacted. It would also bar zoning ordinances from excluding mobile homes from any residential zone. [2][3][6]

Other 2026 housing bills (all pending)

HB 5585 is one of five zoning bills (HB 5581 to 5585) introduced together on February 24, 2026. The others would limit minimum home sizes (HB 5581), multifamily parking minimums (HB 5582) and setbacks (HB 5583), and would make duplexes a permitted use wherever single-family homes are allowed (HB 5584). All five were in the House Committee on Government Operations as of October 10, 2026.

Four more ADU bills were introduced on June 16, 2026 and referred to the same committee:

• HB 6082 would let you convert a building that is at least 10 years old into an ADU without meeting the code's frost-protection foundation rules, if a structural engineer finds no significant frost heaving.
• HB 6083 would stop zoning ordinances from restricting non-fire-rated windows in an ADU that is more than 12 feet from all other structures.
• HB 6084 would create a state income tax credit of 20% of the cost of building an ADU on the same property as your principal residence.
• HB 6085 would stop zoning ordinances from restricting an ADU's connection to the main home's sewer, if the same person owns both and they are on the same parcel.

None of these bills is law. Check the bill pages on the Michigan Legislature website for updates. [6][7][8][9][10][11][12][13][14][15][16][17][18]

Building permits and the state construction code

Zoning and building codes are separate. Even where zoning allows an ADU, Michigan law requires, except where the state code provides otherwise, the owner (or the owner's builder, architect, engineer or agent) to apply for a building permit before construction, with plans drawn to scale and a site plan.

The state Department of Licensing and Regulatory Affairs administers and enforces the state construction code, except where a county, city, village or township has taken over that job by ordinance. Your local building department will tell you which office handles your permits.

Local building offices may add their own requirements. For example, Grand Rapids says its ADUs are subject to the Michigan Residential Code, that a licensed residential contractor must apply for the permits, and that the main house and the ADU must be fire separated with one-hour rated walls and ceiling assemblies. [19][20][21][22]

State programs: MSHDA

The Michigan State Housing Development Authority (MSHDA) works on ADUs through local governments. Its Housing Readiness Incentive Grant Program, described on MSHDA's Get Housing Ready page, gives cities, counties, townships and villages (not homeowners) up to $50,000 for work such as master plan updates and zoning text amendments that increase housing supply. MSHDA says the program "has limited funding available effective September 16, 2026."

MSHDA's Get Housing Ready guide, on the same page, suggests that local governments "Enable homeowners to add ADUs in all residential zones." MSHDA calls the guide "a suggested starting point, not a prescriptive checklist," so it does not change your local rules. [23][24]

Local examples: Grand Rapids, Ann Arbor and Detroit

Grand Rapids. The city's ADU FAQ (August 2026) says ADUs "are permitted as accessory uses on all single- and two-family residential lots." It says the zoning ordinance "was updated in June 2026 to allow ADUs of up to 1,000 square feet," and an ADU may never be larger than the main house. The City Commission adopted Ordinance No. 2026-15, amending the zoning ordinance's ADU section, on June 16, 2026. Detached ADUs may not be taller than 25 feet. You may rent an ADU, but not for fewer than 30 days, and a rented ADU must be registered and certified as a rental. A deed restriction saying the ADU won't be sold separately from the house must be recorded.

Ann Arbor. The city's ADU Guidebook (September 2023) says ADUs are allowed in the R1, R2, R3 and R4 districts, only on a lot with a single-family home, one per home. The maximum size is 600 sq ft on lots up to 7,199 sq ft and 800 sq ft on larger lots, but never more than the ground floor of the main house. Rentals of less than 30 days are prohibited. The city's ADU page says no site plan, public hearing or public notice is required, but you need building permits. The guidebook is from 2023, but the city's current Unified Development Code (11th edition, effective August 10, 2025, Section 5.16.6.D) has the same size limits and 30-day rental rule. Confirm the current rules with Planning Services at (734) 794-6265.

Detroit. In 2025 the city proposed a "Let's Build More Housing" zoning amendment. Its briefing says ADUs are "Currently barred in R2, and in R3 – R6 requires special City approvals (i.e., variances)," and would remain barred in R1. The proposed ordinance text (revised October 16, 2025) would allow one detached ADU per lot in R2 to R6, up to the smaller of 1,200 sq ft or 60% of the main home's floor area. The city's Build More Housing page says the proposal "has been submitted to City Council" and that the Council "will not vote on these changes in 2025 but may choose to consider them in 2026." As of October 10, 2026, that city page still describes the changes as a proposal before City Council, so check with the city before you plan a Detroit ADU. [22][25][26][27][28][29][30][31]

What to check with your local government

Because the rules are local, ask your city, village or township planning or zoning office:

• Whether ADUs are allowed in your zoning district, and whether they are a permitted use or a special land use that needs a hearing.
• Whether attached, detached or garage ADUs are allowed, and the maximum size, height and setbacks.
• Whether the owner must live on the property, and how many parking spaces you need.
• Whether you can rent the ADU, and for how long (Grand Rapids and Ann Arbor ban rentals shorter than 30 days).
• Whether the ADU can share water and sewer with the main house.
• Which office issues building permits, and the permit fees.

Our ADU permit process guide, garage conversion guide, ADU cost guide and basement apartment guide cover the general steps. [1][4][20][22][26]

Michigan laws to know

• Michigan Zoning Enabling Act, MCL 125.3201

  Lets each local unit of government regulate land use and the location, height, bulk, uses and size of dwellings, which is where local ADU rules come from. [1]

• Michigan Zoning Enabling Act, MCL 125.3502 (special land uses)

  Lets a zoning ordinance make a use a special land use that needs review and approval, with notice to neighbors within 300 feet. [4]

• Stille-DeRossett-Hale Single State Construction Code Act, MCL 125.1508b and 125.1510

  Sets who enforces the state construction code and requires a building permit application before you build. [19][20]

• HB 5585 (2026), proposed ADU law (pending)

  Would make an ADU of up to 800 sq ft (or 75% of the home, if less) a permitted use approved by staff without a hearing, and bar parking and owner-occupancy rules; still in committee. [2][3][6]

Questions people ask