The City says it best: “an Accessory Dwelling Unit is a second, smaller dwelling unit either developed within an existing single-familyhouse (such as in a basement, attic, or addition) or part of an accessory building (such as a converted garage or carriage house).”
ADU's are a great way to increase affordability and improve the environment, both for homeowners and renters. For homeowners, they open up a stream of income on existing property. For renters, they open up much-needed housing.
This map shows the lots that likely are allowed to build an ADU. The green lots are zoned correctly and big enough. The yellow lots are zoned correctly but too small.
We're only allowed one ADU per lot. If everyone built one tomorrow, we'd add over 16,000 units. That's not nearly enough for the 80,000 people who burn fossil fuels to drive in to Ann Arbor every day. But it's a start!
The City of Ann Arbor has a very readable handbook, and of course if you are actually planning on building something, you should contact the City instead of trusting this website.
Last updated March 2020.