Summarizes the regulations of the City of Sonoma for detached accessory dwelling units. The text of the ordinance can be found in Sonoma Municipal Code (SMC) Section 19.50.090, Accessory Dwelling Units.

Unit Type Detached Accessory Dwelling Unit (Detached ADU)
Basic Requirement Primary residence or ADU must be owner occupied. ADU may be a Manufactured Home or Efficiency Unit. SMC 19.50.090.A.1 and Govt. Code 65852.2.(i)(4)
Recordation of a deed restriction required? No
Must be created within a legally established bedroom within the existing walls of the primary? No
10 ft. Minimum Separation from the Main Dwelling? Yes SMC 19.50.090.B.3
Lot Coverage and Floor Area Ratio shall be met? Yes SMC 19.50.090.B.3
Building Setbacks Required? Yes See SMC Chapter 19 and SMC 19.50.090.B.4
ADU Setback from Main Dwelling 10 Feet Minimum.
Separate Entrance Required? Yes CRC R311.1
Kitchen Required? Yes SMC 19.92.020.A
Bathroom Required? Yes SMC 19.92.020.A
Minimum Dwelling Unit Area 150 s.f. SMC 19.50.090.B.2.b
Minimum Habitable Room Size 70 sq. ft. (except kitchens). CRC R304.1
Minimum Habitable Room Dimension 7 feet in any horizontal direction, (except kitchen). CRC R304.2
Maximum Floor Area 850 s.f.; If the ADU exceeds 650 s.f. the area shall not exceed 50 percent of the existing living area of the main dwelling. SMC 19.50.090.B.2.b
Maximum Building Height One story maximum; SMC 19.50.090.B.5; Also see SMC 19.40.040
Maximum Occupancy? Not specified
Can Be Rented? If for 30 days or more. SMC 19.50.090.A.3
Building Permit Required? Yes CA Residential Code 106.1 as amended by the Sonoma Municipal Code
Fire Sprinkler System Required? If installed or required in the primary dwelling. Govt. Code 65852.2(e) and SMC 14.10.045 ‐ 2016 California Fire Code amendment of section 903.2
1-Hour Fire-Resistive Wall Separation Required Between Dwelling Units? Not applicable
New or Separate Sewer Connection Required at Street Main? Possibly – Check with Sonoma County PRMD. Govt. Code 65852.2(f)(2)(B)
Sewer Connection or Capacity Fees Required? Possibly – Check with Sonoma County PRMD. Govt. Code 65852.2(f)(2)(B)
New or Separate Water Connection Required at Street Main? No, if ADU is created within existing space. Required if larger water service lateral or water meter is needed due to inadequate water service size. Govt. Code 65852.2(f)(2)(A)
Water Connection Fee Required? Only if new water meter is needed due to inadequate size. Meter charge only! Govt. Code 65852.2(f)(2)(B)
Water Capacity Fees Required? No Govt. Code 65852.2(f)(2)(B)
Zoning Districts Where Allowed? R-HS, R-R, R-L, R-S, R-M, R-H, R-O, and R-P
School Impact Fees Required? If more than 500 s.f.
Additional Parking Spaces Required? Possibly SMC 19.50.090.E
Landscaping Required? If ADU is located within 15 feet of an adjoining residence. SMC 19.50.090.B.8

What is an “accessory dwelling unit”?

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)

“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.]

Where are accessory dwelling units allowed?

  • 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-conforming 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.

Who can live in an accessory dwelling unit?

Anyone can live in an accessory 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.

What permits are required for accessory dwelling units?

A building permit is required for all proposed dwelling unit types.