Accessory Dwelling Units (ADUs)

An accessory dwelling unit is an attached or detached residential dwelling unit which provides complete independent living facilities for one or more persons, and includes separate permanent provisions for entry, living, sleeping, eating, cooking, and sanitation on the same parcel as a single-family dwelling. An accessory dwelling unit may also be provided as an efficiency dwelling unit and/or a manufactured home. (SMC 19.92.020.A)

A junior accessory dwelling unit is a living space not exceeding 500 sq. ft. in size and contained entirely within an existing single-family dwelling. A junior accessory dwelling unit shall include an efficiency kitchen, and may include separate sanitation facilities or share sanitation facilities with the existing structure. (SMC 19.92.020.A)

“Efficiency dwelling unit” means a small, self-contained dwelling unit (occupied by no more than two persons^[1]) containing a (only one¹) habitable room of not less than 150 square feet of floor area and a minimum horizontal dimension of seven feet. Bathrooms, toilet rooms, closets, halls, storage or utility spaces and similar areas are not considered habitable rooms [The City Planning Department considers “a small, self-contained dwelling unit” to be a dwelling unit not exceeding 850 square feet in floor area.]

  “Dwelling unit” defined.

“Dwelling,” “dwelling unit,” or “housing unit” means a room or group of internally connected rooms that have sleeping, cooking, eating, and sanitation facilities, but not more than one kitchen, which constitute an independent housekeeping unit, occupied by or intended for one household on a long-term basis. (SMC 19.92.020.D)

 “Efficiency kitchen” defined.

“Efficiency kitchen” means a removable kitchen that contains a sink with a maximum [vertical] waste line diameter of 1.5 inches; appliances that do not require electrical service greater than 120 volts, or natural or propane gas; a limited food preparation counter; and storage cabinets. The entire kitchen shall not exceed six lineal feet, except that if existing counter space is being converted to efficiency kitchen use then the counter space shall not exceed eight lineal feet. [Examples of prohibited cooking appliances are: ranges, stoves, cook tops, and built-in ovens. Examples of cooking appliances that may be used are: microwave ovens, hot plates, and similar appliances intended for use on top of a countertop.  Refrigerator size is not limited.]

[1] See CA Health & Safety Code 17958.1

See the Accessory Dwelling Unit Requirements.

The following applies to Accessory Dwelling Units, Junior Accessory Dwelling Units, and Efficiency Dwelling Units:

• Accessory dwelling units are allowed in the R-HS, R-R, R-L, R-S, R-M, R-H, R-O, and R-P zones.
• An accessory dwelling unit shall not be located on any parcel already containing a dwelling unit that is non-confirming with respect to land use or density, or developed with a duplex, triplex, apartment, planned development, or condominium. No more than one accessory dwelling unit shall be located on a parcel.
• An accessory dwelling unit may be within, attached to, or detached from the primary dwelling unit. A detached accessory dwelling unit may take the form of a manufactured home on a permanent foundation. If detached, the accessory dwelling unit shall be separated from the main dwelling unit a minimum of 10 feet.

See the Accessory Dwelling Unit Requirements.

For additional information or to discuss a particular location, contact the Planning Department.

Anyone can live in an accessory dwelling unit, junior accessory dwelling unit, or efficiency dwelling unit. The owner of the property shall reside on the property in either the main or accessory dwelling unit (upon construction). Accessory dwelling units, junior accessory dwelling units, or efficiency dwelling units may be rented for periods of 30 days or more. The rental of an accessory unit for periods of less than 30 days is prohibited.

The City’s municipal code requires that one off-street parking space with an all-weather surface shall be provided for the exclusive use of the ADU, in addition to the parking that is required for the primary dwelling. The parking space for the ADU may be allowed in the driveway and in tandem.  However, the parking requirement is waived for certain locations (e.g. if the ADU is located within a designated historic district or within a half mile of a public transit stop), for certain types of ADUs (e.g. when the ADU is part of the existing single-family dwelling or an existing accessory structure) and for ADUs meeting other criteria listed in SMC 19.50.090E.  Check with the Planning Department to help determine the requirements for your ADU.

Yes, a building permit is required for all proposed dwelling unit types.

Fire-Resistive Construction. Pursuant to Section R302of the CA Residential Code as amended by the City of Sonoma, Dwelling units in two-family dwellings shall be separated from each other by wall and floor assemblies having not less than a 1-hour fire-resistance rating where tested in accordance with ASTM E119 or UL 263. Fire-resistance-rated floor/ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend from the foundation to the underside of the roof sheathing.

Automatic Fire Sprinkler Systems. Pursuant to CA Govt. Code Section 65852.2(c) & (e) [Effective 1/1/17], CA State Fire Marshal Information Bulletin 17-001 and Chapter 14.10.045 of the Sonoma Municipal Code, an automatic fire sprinkler system is required for:

New detached accessory dwelling units when: The primary dwelling on the property has or will have as a result of the current project, an automatic fire sprinkler system installed; OR the detached accessory dwelling unit floor area exceeds 1,200 sq. ft.

New attached accessory dwelling units constructed within or added to an existing primary residence when: The existing primary dwelling on the property already has an automatic fire sprinkler system installed; OR the addition to or alteration of the existing primary dwelling to facilitate the creation of an attached accessory dwelling unit (including the subject ADU project), plus any other building permits issued for the building within any 36 month period, exceeds a total permit valuation of $100,000.

For more information about building permit requirements, visit the Building Department page.

• Attached accessory dwelling unit. The minimum floor area is 150 s.f.  The minimum dimension of any habitable room, except kitchens, is 7 feet in any horizontal direction (CA Residential Code R304.2).  The minimum ceiling height shall comply with the CA Residential Code. The maximum size is 30 percent of the existing living area of the main dwelling.
• Detached accessory dwelling unit. The minimum size is 150 sq. ft. The minimum dimension of any habitable room, except kitchens, is 7 feet in any horizontal direction (CA Residential Code R304.2).  The minimum ceiling height shall comply with the CA Residential Code. The maximum floor area is 850 sq. ft. Any detached accessory dwelling unit exceeding 650 sq. ft. shall not exceed 50 percent of the existing living area of the main dwelling.
• Junior accessory dwelling unit. The minimum size of habitable rooms, except kitchens, is 70 sq. ft. (CA Residential Code R304.1). The minimum dimension of any habitable room, except kitchens, is 7 feet in any horizontal direction (CA Residential Code R304.2).  The minimum ceiling height shall comply with the CA Residential Code.  The maximum floor area is 500 sq. ft. and all applicable residential zoning district requirements regarding coverage and floor area ration shall be met.
• Efficiency dwelling unit.  The habitable room shall be not less than 150 s.f. of floor area with a minimum horizontal dimension in any direction of 7 feet. Bathrooms, toilet rooms, closets, halls, storage or utility spaces and similar areas are not considered habitable rooms. The minimum dimension of any habitable room, except kitchens, is 7 feet in any horizontal direction (CA Residential Code R304.2).  The minimum ceiling height shall comply with the CA Residential Code. The maximum floor area of an efficiency dwelling unit is 500 s.f.

Each accessory dwelling unit, junior accessory dwelling unit, and efficiency dwelling unit shall comply with the height limitations established in the zoning district where the structure is located. Detached accessory dwelling units shall be limited to a single story and shall comply with height restrictions for accessory structures. Attached accessory dwelling units shall comply with height restrictions for primary structures.

See the Accessory Dwelling Unit Requirements.

For additional information or to discuss a particular location, contact the Planning Department.

Accessory dwelling units, junior accessory dwelling units, or efficiency dwelling units may only be rented for periods of 30 days or more.  The rental of an accessory unit for periods of less than 30 days is prohibited.