Zoning & Size Limits
| Requirement | Ann Arbor, MI | Grand Rapids, MI |
|---|
| Allowed Zones | R1, R2, R3, and R4 districts, on lots containing one single- | By right on single- and two-family residential lots citywide |
| Max Size (Detached) | 600 sq ft on lots up to 7,199 sq ft; 800 sq ft on lots 7,200 sq ft or larger — or the ground-floor area of the main dwelling, whichever is less | 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 |
| Max Size (Attached) | Same tiered cap: 600 sq ft (lots under 7,200 sq ft) or 800 sq ft (lots 7,200 sq ft+), or the main dwelling's ground-floor area, whichever is less | Same cap: 850 sq ft and 40% of the primary dwelling's gross floor area |
| Max Height | 21 ft for an ADU in an accessory building (detache | 25 ft for a detached ADU that meets the zone's pri |
| Parking Required | No additional parking required — the parking requirement was | No additional parking required — parking requirement elimina |
| Owner Occupancy | Not required — the owner-occupancy requirement was removed b | Not required — removed by the 2024 amendments (previously AD |
Setback Requirements
| Setback | Ann Arbor, MI | Grand Rapids, MI |
|---|
| Rear Setback | Allowed in the rear setback area if at least 3 ft from any lot line and all structures cover no more than 35% of the rear setback area; fire-rated walls required if 3-5 ft from a lot line | 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) |
| Side Setback | Detached ADU allowed in the side setback area if farther from the street than the main building (and neighbors' main buildings) and at least 3 ft from any lot line; fire-rated walls if 3-5 ft. Attached ADUs may not be in the required 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 |
| Front Setback | Not permitted within the required front setback ar | Detached ADU may not be located forward of the hou |
Permits & Timeline
| Detail | Ann Arbor, MI | Grand Rapids, MI |
|---|
| Permit Timeline | No hearings required, so review runs on standard building-permit timelines — confirm current plan-review turnaround with Ann Arbor Planning Services (734-794-6265) | 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) |
| Permit Fees | Building and trade permit fees are based on construction valuation — confirm current fee schedule with the Ann Arbor Building Department | Building, trade, and water/sewer connection permit fees based on project scope — confirm current fee schedule with the Grand Rapids Development Center |
| Impact Fees | None — Michigan law does not authorize municipal development | None — Michigan law does not authorize municipal development |
| Pre-Approved Plans | No city pre-approved ADU plan library — confirm wi | None yet — the January 2026 ADU Task Force recomme |
Construction Costs
| Cost | Ann Arbor, MI | Grand Rapids, MI |
|---|
| Avg Build Cost | $120,000-$240,000 | $90,000-$200,000 |
| Cost Per Sq Ft | $180-$300 | $150-$250 |
| Garage Conversion | $60,000-$130,000 | $50,000-$110,000 |
| Prefab ADU | $90,000-$180,000 | $80,000-$160,000 |
Rental Income Potential
| Rental | Ann Arbor, MI | Grand Rapids, MI |
|---|
| 1BR Avg Rent | $1,450-$1,650/mo | $1,400-$1,470/mo |
| 2BR Avg Rent | $1,900-$2,000/mo | $1,500-$1,650/mo |
| Short-Term Rentals | No — leasing or renting an ADU for less than 30 days is proh | No — ADUs may not be leased for under 30 days or used as Air |
| Est. ROI | 6-10% annual return | 7-11% annual return |
Which City Is Better for ADUs?
Ann Arbor scores 7/10 while Grand Rapids scores 7/10 on our ADU-friendliness index.
Both cities offer viable ADU development opportunities — the best choice depends on your specific property, budget, and goals.
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