Zoning & Size Limits
| Requirement | Grand Rapids, MI | Detroit, MI |
|---|
| Allowed Zones | By right on single- and two-family residential lots citywide | Currently not permitted in R1/R2; the pending 'Let's Build M |
| Max Size (Detached) | 850 sq ft maximum and no more than 40% of the main house's gross floor area (ordinance §5.9.03 allows at least 400 sq ft in any case); greenspace requirements (30-60% depending on zone) can further limit buildable size | Proposed: no more than the smaller of 1,200 sq ft or 60% of the principal dwelling's gross floor area (Sec. 50-12-466); not yet in effect |
| Max Size (Attached) | Same cap: 850 sq ft and 40% of the primary dwelling's gross floor area | Proposed rules allow only detached ADUs — the unit must be detached from the principal residence (it may be freestanding or combined with a garage, on any story including above the garage) |
| Max Height | 25 ft for a detached ADU that meets the zone's pri | Proposed: 25 ft maximum for ADUs per the amended d |
| Parking Required | No additional parking required — parking requirement elimina | Proposed: no additional parking required, and if the ADU rep |
| Owner Occupancy | Not required — removed by the 2024 amendments (previously AD | No owner-occupancy requirement appears in the proposed ordin |
Setback Requirements
| Setback | Grand Rapids, MI | Detroit, MI |
|---|
| Rear Setback | Detached ADU must be at least 3 ft from the rear lot line (special Building Code requirements if a wall is within 5 ft of the property line) | Proposed: standard 3 ft accessory-structure rear setback, with no rear setback required where the lot abuts an alley; existing accessory structures converted to ADUs may keep their footprint |
| Side Setback | At least 3 ft from side lot lines; also at least 6 ft from the house and 3 ft from any other accessory structure | Proposed: 3 ft from side lot lines (accessory-structure standard); ADU must also be at least 10 ft from the principal building, 5 ft from its porch/deck, and 10 ft from any electrical line unless BSEED waives it |
| Front Setback | Detached ADU may not be located forward of the hou | Proposed: ADUs may not be located in a front yard |
Permits & Timeline
| Detail | Grand Rapids, MI | Detroit, MI |
|---|
| Permit Timeline | Standard building-permit review since no Planning Commission hearing is required (unless seeking the 20-to-25-ft height increase via Special Land Use) — confirm current turnaround with the Development Center (616-456-3000) | Not applicable until the ordinance is adopted — City Council was still deliberating as of spring 2026 |
| Permit Fees | Building, trade, and water/sewer connection permit fees based on project scope — confirm current fee schedule with the Grand Rapids Development Center | Building permit fees based on construction value — confirm with Detroit BSEED once ADU rules take effect |
| Impact Fees | None — Michigan law does not authorize municipal development | None — Michigan law does not authorize municipal development |
| Pre-Approved Plans | None yet — the January 2026 ADU Task Force recomme | None for ADUs — confirm with the Detroit Planning |
Construction Costs
| Cost | Grand Rapids, MI | Detroit, MI |
|---|
| Avg Build Cost | $90,000-$200,000 | $90,000-$200,000 |
| Cost Per Sq Ft | $150-$250 | $140-$240 |
| Garage Conversion | $50,000-$110,000 | $45,000-$100,000 |
| Prefab ADU | $80,000-$160,000 | $75,000-$150,000 |
Rental Income Potential
| Rental | Grand Rapids, MI | Detroit, MI |
|---|
| 1BR Avg Rent | $1,400-$1,470/mo | $950-$1,300/mo |
| 2BR Avg Rent | $1,500-$1,650/mo | $1,100-$1,500/mo |
| Short-Term Rentals | No — ADUs may not be leased for under 30 days or used as Air | Proposed ordinance prohibits renting an ADU for 27 or fewer |
| Est. ROI | 7-11% annual return | 8-12% potential annual return once ADUs are legalized — not currently buildable in most districts |
Which City Is Better for ADUs?
Grand Rapids scores 7/10 while Detroit scores 2/10 on our ADU-friendliness index.
Grand Rapids edges ahead overall. Both cities offer viable ADU development opportunities — the best choice depends on your specific property, budget, and goals.
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