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ADU rules in Michigan

Representative cities: Detroit, Grand Rapids.

Verify locally. Michigan enforces the 2015 Michigan Residential Code statewide (administered by LARA); municipalities issue permits and may add local amendments. Footings must reach below the local frost line (≈42 in around Detroit/Grand Rapids). Always confirm exact requirements and fees with Detroit or Grand Rapids before starting work. ADU rules below are drawn from official sources — always confirm with the issuing building department before designing or building.

ADU permit rule

Permit requiredGenerally allowedcity authority
Fee basis
Building permit based on project valuation; verify with the city. Detroit issues residential permits in about 5 days.
Typical timeline
Typically 5–15 business days; Detroit ~5 days, Grand Rapids 5–10 days for simple projects.
Setback
Follow local zoning setbacks and lot-coverage limits; confirm with the city planning department.
Area threshold
No state size exemption for an ADU (it is habitable space).
Exempt if
None — ADUs always require a building permit and zoning approval.
Go / no-go
allowed
ADUs are allowed in Michigan subject to local zoning. A building permit and zoning approval are required; some cities cap size and occupant/rental rules. Confirm with Detroit or Grand Rapids planning.
ADU official sources: Michigan LARA — Bureau of Construction Codes (2015 Michigan Residential Code) · City of Detroit — Do I Need a Building or Trade Permit? · City of Grand Rapids — Apply for a Residential Building Permit
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Frequently asked questions

Do I need a permit to build an ADU in Michigan?

Per Michigan rules, an ADU is "yes" for a permit and the authority is "city". ADUs are allowed in Michigan subject to local zoning. A building permit and zoning approval are required; some cities cap size and occupant/rental rules. Confirm with Detroit or Grand Rapids planning. Always confirm with the issuing building department.

How big can an ADU be in Michigan?

Area threshold: No state size exemption for an ADU (it is habitable space).

What are the ADU setbacks in Michigan?

Setback: Follow local zoning setbacks and lot-coverage limits; confirm with the city planning department.

How much does an ADU permit cost in Michigan?

Fee basis: Building permit based on project valuation; verify with the city. Detroit issues residential permits in about 5 days.

State-wide sources: Michigan LARA — Bureau of Construction Codes (2015 Michigan Residential Code) · City of Detroit — Do I Need a Building or Trade Permit? · City of Grand Rapids — Apply for a Residential Building Permit

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