Accessory Dwelling Units, known as ADUs, are small interior apartments or separate backyard houses associated with single family houses.  People also call them mother-in-law apartments, granny flats, or alley houses. There are many names. These units are currently allowed in Missoula’s multifamily zoning districts, and the City Council is currently considering whether to allow some version of ADUs in single family zoning districts.

In the zoning code, Accessory Dwelling Units are defined as separate dwelling unit within a primary residence or a separate dwelling unit that occupies an accessory building that shares a parcel with a primary residence. As the name implies, accessory dwelling units are an accessory use to the principal use of the property (i.e., a detached house). (See also the accessory dwelling unit regulations of 20.45.060.)