- What is an accessory dwelling unit (ADU)?
- Where are accessory dwelling units currently permitted?
- What is a second dwelling unit?
- Is every residentially zoned parcel eligible to build an ADU?
- How is a primary dwelling with an attached ADU different than a duplex?
- What is a dwelling unit?
- How many accessory dwelling units are allowed on my property?
- Are there minimum parcel size requirements?
- Who can occupy the accessory dwelling unit?
- How will owner occupancy be enforced?
- Will there be design standards for ADUs?
- Will additional parking be required for an ADU?
- What permits will be required?
- What if I have an undocumented existing second dwelling unit?
- What is my zoning?
What is an accessory dwelling unit (ADU)? top
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 or granny flats.
An ADU is a dwelling that is subordinate to the primary residence and is subject to design standards, required owner occupancy, parking requirement, and size restrictions. An ADU may come in the form of an attached unit to a primary residence or detached accessory structure (such as a basement, attic or garage), or may built to stand alone.
Title 20, Missoula Zoning Code defines an accessory dwelling unit as follows:
Accessory Dwelling Unit
A 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).
Where are accessory dwelling units currently permitted?top
ADUs are currently permitted in multi-dwelling and two-dwelling districts (zones RT5.4, RT2.7, RM2.7, RM1, RM1.5 RM0.5, RMH B, C and M1R) on parcels occupied by a single primary residence and meet the minimum parcel size requirement for the particular district. ADUs are not currently permitted in Single Dwelling Residential Zones. Please see linked Single Dwelling Residential Zones Map.
What is a second dwelling unit?top
A second dwelling unit differs from an ADU in that it is one of two primary residences on a parcel. A second dwelling can be a unit that is detached or attached to another unit (i.e. a duplex), and may be conforming, non-conforming, or illegal. Reference to structures that appear to be ADUs that were established prior to 2009 are more appropriately termed second dwelling units because the term ADU did not exist in Missoula’s zoning ordinance until 2009.
Conforming units – A second unit conforms because it was constructed according to all current requirements of the zoning district. This development type could occur in any residential district as long as the parcel area is sufficient to meet the requirement of 2x the minimum parcel size along with the other required development standards.
Non-conforming units – A second unit is non-conforming because it was legally constructed meeting all the zoning regulations in place at the time of construction. The zoning regulations changed after construction and the unit no longer conforms. This development type could occur in situations where zoning did not exist when the structure was first established but zoning was applied later or upon annexation or through changes to zoning over time.
Illegal units – A second unit may be illegal having been constructed without review or permits of any kind, and does not meet the current zoning requirements.
Is every residentially zoned parcel eligible to build an ADU?top
No. There are many parcels that do not meet the requirements to permit an ADU. Proposed parcels must comply with the specifics of the proposed accessory dwelling unit chapter in Title 20, must contain only one primary dwelling unit, and must meet the minimum parcel area required by the zoning district.
How is a primary dwelling with an attached ADU different than a duplex? top
Accessory dwelling units have specific design standards, are limited in size, are not included in the land area calculation, need only one parking space, and require owner occupancy. Duplex units are not subject to the accessory dwelling unit regulations.
What is a dwelling unit?top
Title 20, Missoula Zoning Ordinance defines a dwelling unit as follows:
A single unit providing complete, independent living facilities for one or more persons, including permanent provisions for living, sleeping, eating, cooking and sanitation. The intent is to be consistent with the building code.
Commentary: The presence of the following are indicators of a dwelling unit: counters, stove, refrigerator, sink, 220V electrical outlet, and bathroom including bathing facilities. In addition, the unit shall have independent access and no access from another dwelling unit. This is not an exhaustive list. One of these indicators on its own is not proof of a dwelling unit.
How many accessory dwelling units are allowed on my property?top
Parcels that are eligible for an accessory dwelling unit would be allowed one ADU per parcel.
Can an ADU be placed on a parcel with two or more primary residences?top
No. A parcel containing more than one primary residence would not be allowed to have an ADU.
Are there minimum parcel size requirements?top
Yes. Parcels must meet the minimum parcel size required by the zoning district. For instance, a parcel in the zoning district R5.4 would require 5,400 square feet of land to be eligible for an ADU.
Who can occupy the accessory dwelling unit?top
The property owner, a family member, or a renter may occupy either the primary residence or the accessory dwelling unit, however; the property owner must occupy one of the two units.
How will owner occupancy be enforced? updated Oct. 16 top
Land owners eligible and choosing to have an ADU on their parcel must file a deed restriction stating they will occupy one of the units on site. The deed restriction must be approved by the City Attorney’s Office and filed with the County Clerk and Recorder’s Office prior to approval and/or occupancy of the ADU.
Once the deed restriction is on file, enforcement will be complaint-based. A complaint against the ADU/property-owner will set in motion a process involving enforcement by a City Code Enforcement Official, and if necessary the City Attorney’s office, until the deed-restriction is honored.
Will there be design standards for ADUs? top
Yes. The complete list of current standards can be found in the Missoula City Zoning Ordinance, Title 20 (Ch. 20.45.060) Some of these standards may be discussed if the City Council decides to go forward with a proposal. A short list of current design standards follows:
- ADUs may be detached, attached to a primary dwelling, or attached to an accessory building.
- The property owner must reside in one of the units.
- An ADU may not exceed 800 square feet in area.
- One off street parking space must be added for the ADU.
- Exterior architectural features of the ADU must be similar to the primary residence.
- One ADU may be added to a parcel with an existing primary dwelling unit and meeting minimum parcel requirements.
Will additional parking be required for an ADU?top
Yes. An accessory dwelling unit will require one dedicated off street parking space be added to the parcel.
What permits will be required?top
Construction of a new accessory dwelling unit (attached or detached) and renovations of existing structures to include an ADU will be subject to all permitting requirements of the City of Missoula.
What if I have an undocumented existing second dwelling unit?top
The Planning Office will determine if the dwelling is considered a second unit or an accessory dwelling unit. If it is considered a second unit (as described above) the general standards of the zoning district or the nonconforming uses chapter (Ch.20.80 Nonconformities) may apply. If the unit can meet the definition of an accessory dwelling unit and passes a safety inspection provided by the Building Department, appropriate permits must be obtained and documentation filed to make the unit legal.
The City Council has a great interest in the safety of citizens renting existing undocumented dwelling units and is considering including a grace period in the permitting process to encourage those property owners with undocumented units to bring them up to current safety standards.
The City Building Division currently has a voluntary housing inspection program. The purpose of the program is to improve the quality of residential structures in the City of Missoula. The inspection will cover a checklist of items that constitute a substantial health and safety risk to the occupants and owners, and can be requested by landowners, agents, or tenants. To obtain an inspection, fill out a request form provided by the City Building Department (552-6044) and pay an original inspection fee of $15.00.