ADU Guide · Verified 2026
Building an ADU in Michigan
Michigan has no statewide ADU mandate, and Detroit, the state's largest city, currently prohibits ADUs on most residential lots outright. A city-approved amendment would change that, but the City Council had not yet adopted it as of this research.
Quick Facts
Statewide floors set by No statewide ADU law; local zoning controls. Your city may be more generous but cannot go below them.
The Three Types of ADU
A real, current prohibition in the state's largest city
Detroit doesn't just lack an ADU-friendly ordinance, it actively prohibits ADUs on most residential lots today. This is a real, current ban rather than the vague "check locally" uncertainty found in many other cities across this research.
A change that's approved but not yet adopted
Detroit's own City Planning Commission approved a real amendment, "Let's Build More Housing," on October 16, 2025, that would allow detached ADUs by right, but the City Council had not yet voted to adopt it as of this research. This is worth confirming directly with the city before assuming either the old ban or the new rule applies.
Ann Arbor shows what the alternative looks like
Ann Arbor already permits ADUs directly in its R1 through R4 residential zones, a real, working example of a Michigan city that took the opposite approach from Detroit's current prohibition.
What people get wrong
The most common mistake is assuming Detroit's pending amendment is already in effect because the Planning Commission approved it. City Council adoption is a separate, additional step, and the amendment was not yet law as of this research.
From Idea to Move-In: The Timeline
Who Administers It
Counties With Their Own Rules
These Michigan counties have verified, county-specific ADU rules that add to the state baseline:
Building It Yourself? Here's What You'll Need
Planning an ADU? Tools homeowners use in the design and layout phase:
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Check Your Local Rules
Your city may allow more than the state floor
State law sets the minimum; many Michigan cities and counties are more generous. Browse the full directory of 83 counties and every city in Michigan for local rules, fees, and building department contact details.
Browse the full Michigan directory →Not sure if your project needs a building permit, a zoning approval, or both? See our guide to building permits vs. zoning approval.
Official Sources
ADU law changes frequently and local ordinances add detail. This guide is general information, not legal advice, always confirm with your local building department. Reviewed by the StateDataIndex Editorial Team · Updated September 2026.