Accessory Dwelling Units

The City of Missoula adopted an update to our zoning code (Title 20) on October 19, 2020. This update included changes to standards and restrictions on Accessory Dwelling Units (ADUs), many of which are based on the implementation recommendations in "A Place to Call Home." Click on the Important Links widget on the sidebar of this page to see Title 20, or contact the Zoning Desk on call with any building and permits questions related to ADU's (see Who's Listening)!

What is an Accessory Dwelling Unit?

Accessory Dwelling Units, known as ADU's, are small interior apartments or separate backyard houses that share a parcel with a single-family residence even if the density limit through zoning would otherwise not allow another housing unit on that property. ADU's are also known as mother-in-law apartments or backyard cottages. ADU's are called 'accessory' because they are lesser in size and presence to the primary dwelling on a property. The difference between an 'accessory' and any other dwelling unit is that an ADU stays at that accessory scale, as opposed to more primary dwelling units on the same property (i.e., a duplex), which would be permitted only if they were still within the density range allowed by zoning.

Why Do ADUs Matter?

The City of Missoula adopted "A Place to Call Home," our citywide housing policy in 2019. The policy recommends use of Accessory Dwelling Units in order to provide affordable, accessible housing that could be easily distributed throughout the city. ADU's provide a wide range of benefits, including supplemental income to finance-burdened home owners, affordable housing options for students and young families, a type of residential infill that is compatible with existing neighborhoods, and the ability for families to provide live-in options for aging parents or adult children needing extra care or services. The implications of the COVID-19 pandemic especially illustrate how the benefits of caring for aging parents at home rather than in long-term care facilities may further spur the demand for ADU-type living arrangements. For more information on the benefits of ADUs, see Important Links to the right for articles and resources.

Where Can You Build an ADU?

The City of Missoula allows ADU's in all residential zoning districts within the city limits. (NOTE: This does not include Special Districts). ADU's in the city are held to certain size and design standards, which have changed over time as the community's concerns and perceptions of ADU's have evolved. Adding an ADU to your property requires building permit review and approval.

The City currently allows three types of ADU's:

• Internal ADU - created within an existing or new house. For example, a basement apartment.
• Internal Addition ADU - added to the floor area of an existing house.
• Detached ADU – a dwelling unit that is separate from the primary dwelling unit. For Example, a garage apartment or alley house.