Everything homeowners ask about building an ADU in Ann Arbor — answered with 2026 data.
Yes, ADUs are allowed in R1, R2, R3, and R4 districts, on lots containing one single-family dwelling (not permitted on lots with a duplex or multi-family building) in Ann Arbor, MI. The maximum size for a detached ADU is 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. Attached ADUs can be up to 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. Ann Arbor has an ADU-friendliness score of 7/10. Check our full Ann Arbor ADU rules page for complete zoning details.
ADU construction in Ann Arbor typically costs $120,000-$240,000. The cost per square foot averages $180-$300. Garage conversions are more affordable at $60,000-$130,000, while prefab ADUs cost $90,000-$180,000. Permit fees add Building and trade permit fees are based on construction valuation — confirm current fee schedule with the Ann Arbor Building Department to your budget. See our detailed Ann Arbor ADU cost guide.
Detached ADUs in Ann Arbor can be up to 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. Attached ADUs are limited to 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. Junior ADUs (JADUs) have a cap of Not applicable — Michigan cities have no separate JADU category. Maximum height is 21 ft for an ADU in an accessory building (detached); 30 ft for an ADU within the main dwelling. You are allowed up to One ADU per single-family detached dwelling; ADU occupancy limited to 2 persons plus offspring, and 4 persons plus offspring combined across both units on a qualifying lot.
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. 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. Front setback: Not permitted within the required front setback area (average of buildings within 100 ft, up to 40 ft max, in established neighborhoods). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
No additional parking required — the parking requirement was removed by the June 2021 amendments. Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required — the owner-occupancy requirement was removed by the June 2021 amendments. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Ann Arbor is typically No hearings required, so review runs on standard building-permit timelines — confirm current plan-review turnaround with Ann Arbor Planning Services (734-794-6265). Plan check: Zoning compliance is reviewed as part of the building-permit process; a property survey may be required to verify setbacks. Pre-approved plans availability: No city pre-approved ADU plan library — confirm with Ann Arbor Planning Services.
Average ADU rental income in Ann Arbor: 1-bedroom units rent for $1,450-$1,650/month, 2-bedroom units for $1,900-$2,000/month. Short-term rentals: No — leasing or renting an ADU for less than 30 days is prohibited. Expected ROI: 6-10% annual return.
The minimum lot size for an ADU in Ann Arbor is No minimum lot size (removed in 2021); lot area only determines the 600 vs 800 sq ft size tier. This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Ann Arbor, a garage conversion typically costs $60,000-$130,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.