Accessory Dwelling Units

Skip Navigation LinksHome » Departments » Planning » Accessory Dwelling Units

​​​​​​​​​​​​​​​​​What are Accessory Dwelling Units (ADUs)ADU pic 4.png

An Accessory Dwelling Unit is a second, smaller dwelling unit either developed out of an existing single-family house (such as a basement, attic, or addition) or as part of an accessory structure (such as a converted garage or carriage house). 

Currently, the City of Ann Arbor Zoning Ordinance allows for these units to be developed in the primary residence through a special exemption process, with additional requirements that the occupant is related and not pay any rent.

ADU Fact​ Sheet 2021 (PDF)

ADU Guidebook​​ (PDF)​

Adopted ADU Changes as of 2021 

The proposed changes include allowing ADUs in more zoning districts and relaxing the standards in zoning districts where ADUs are currently allowed. These changes would eliminate the requirement that the ADU must be in an existing detached building; newly constructed detached ADUs will be allowed. The proposed changes would also allow ADUs in the R3 Townhouse and R4A, R4B, R4C, R4D and R4E Multiple-Family Dwelling Districts when the lot has one single-family home on it.​

Interactive Map Tool

An interactive map to explore the potential areas where ADUs would be permitted ​ throughout the City: ADU ​Map​​​

ADU code may be found here​
Please reference ​5.16​.6 D​ - Accessory ​​Uses and Structures. 

February 9, 2021 Planning Commission Working Session

Questions and comments may be submitted in advance to City of Ann Arbor Planning Services by emailing to [email protected].​

Frequently Asked Questions

 How does the creation of an ADU impact property tax assessment?  

The PRE (Primary Residence Exemption) is based on the percentage occupied by the owner, the unit would be assessed similar as a 2 family rental. The assessment would also increase for extra finish and kitchens.

 Why is the owner occupancy requirement included?  

An advantage of the requirement for a property owner to have their primary residence on the parcel is to increase the likelihood that the property will be well managed and properly cared for.  This requirement will eliminate the possibility of converting the units to Short Term Rentals and is expected to reduce the likelihood of loud activities that affect surrounding neighbors.    The language in code requires an ADU property to be deed restricted to ensure that the property owner lives on the site.  A disadvantage of the owner occupancy requirement is that fewer ADUs will likely be provided.

 How will the requirements for lot size, setbacks, and height change?   

 For detached ADUs, the maximum height will continue to be 21 feet.  The ADU structure will continue to be required to provide a minimum of a 3 foot side and 3 foot rear setback and cannot take up more than 35% of the rear yard.  A proposed amendment is to eliminate the minimum lot size for a parcel that could accommodate an ADU.  The existing code requires a minimum of 5,000 square feet.  This change will increase the number of parcels in the City that can accommodate an ADU.

 What is the difference between an ADU and a Short Term Rental?   

Short term rentals do not have owner occupancy limitations and can be rented for up to 30 days.  ADUs have an owner occupancy requirements and must be rented for at least 30 days.

 What are the neighborhood notification requirements for a new ADU?  

No neighborhood notifications requirements exist.  Although no site plan, public hearing, or public notice are required, building permits are necessary for construction.

 How many ADUs have been proposed since the 2016 amendments were approved?  

Since 2016, a total of 23 applications for ADUs have been submitted.  Some are currently under review, some are under construction, and some have been completed.

 The code for ADU's mentions a “family".  What is the City's definition of a “family"?  

 Limits on Occupancy of Dwelling Unit:

  • Dwelling Unit may be occupied by one of the following Family living arrangements:
  • One or more Persons related by blood, marriage, adoption, or guardianship living as a single Housekeeping Unit, in all districts.
  • A maximum of four Persons plus their Offspring living as a single Housekeeping Unit, in all districts.
  • A maximum of six Persons living as a single Housekeeping Unit in Multiple-Family and mixed use districts only.
  • A Functional Family living as a single Housekeeping Unit that has received a Special Exception Use permit pursuant to Section 5.29.5

 How do ADU's advance City planning Goals?  

ADU's advance a number of stated City planning goals including:  a) increasing housing diversity, b) increasing housing affordability (by increasing the supply of new rental housing), c) supporting transit (by increasing density in existing neighborhoods near transit corridors), d) encouraging individuals to age in place or age with family nearby, e) reducing the amount of impervious surface per dwelling unit (since ADU's will be built in neighborhoods that already have streets, driveways and sidewalks), f) allowing property owners a diversity of possible uses by allowing an ADU to be used by an aging relative, used as a home office, used by children of the owner who are returning to town, and/or used as a rental unit for added income.​​

Past ADU Changes


Amendments to the ADU Ordinance were proposed.   These changes included adding ADU's in all Residential Zoning Districts, with the exception of R6 (Mobile Home Parks), used as single-family units, removing side/rear entrance requirements, removing the 5,000-s.f. minimum lot size requirement, and removing the requirement an existing accessory structure must be present prior to 12/31/16 to allow a detached ADU.  These proposed changes were not approved.


Amendments Approved on August 4, 2016, City Council approved amendments on August 4, 2016, to the Zoning Ordinance to allow ADUs in single-family residential zoning districts meeting certain requirements. Below is more information regarding City Council and Planning Commission action history, general information about accessory dwelling units, and resources associated with this planning initiative. 

City Council Action

Second Reading, Public Hearing, and Action Vote - City Council approved amendments to the Zoning Ordinance regarding ADUs following a second reading and a public hearing at the August 4, 2016 meeting. 

First Reading - City Council passed the first reading of the amended proposed ordinance at their July 7, 2016 meeting.  A second reading and vote on the amended proposed ordinance will be held in one month, on Thursday, August 4, 2016.  The Staff Memo (PDF) for the first reading is available. 

Planning Commission Recommendation

On Tuesday, April 19, following a public hearing, the Planning Commission recommended approval of the proposed ordinance (PDF) to the Zoning Ordinance regarding accessory dwelling units.  The Planning Commission also asked staff to develop a draft guidebook for homeowners with information on how to develop an ADU and suggest options on how to preserve the affordability of the ADUs, potentially with the use of other incentives already available to the City.  The draft guidebook will accompany the proposed amendments for City Council consideration.   

Why are we talking about changes?

Ann Arbor's made accommodations in their ordinance to accommodate ADUs in 2001-2002.  However, only 2 units have been applied for and approved.  Since that time, the housing market went through a boom, bust, and recovery.  The 2015 Housing Affordability and Economic Equity Analysis documented increasing housing costs in Ann Arbor in particular, which were pricing out moderate-income and working families as well as young adults and seniors.  One of the recommendations in the study was to consider Accessory Dwelling Units with the lens of adding additional affordable housing units, while also providing some income to existing home-owners which could help existing residents stay in their homes.

Ann Arbor City Council requested that the Planning Commission consider changes to more easily allow for ADUs in Ann Arbor, effectively starting this process.


Subscribe to email updates 
​Planning & Development Services
301 E. Huron St.
Ann Arbor
Planning Manager

Brett Lenart, AICP 
[email protected] 
734.794.6000 x42606


Subscribe to email updates 
​Planning & Development Services
301 E. Huron St.
Ann Arbor


City Planner, Chris Cheng              734.794.6000 x 42616 

[email protected]   ​