Chapter 5 — ACCESSORY AND JUNIOR ACCESSORY DWELLING UNITS

• (a) The purpose of this chapter is to prescribe objective development and site regulations that apply, except where specifically stated, to accessory dwelling units (ADUs) and junior accessory dwelling units (JADUs). This chapter is intended to implement Government Code Sections 66310 to 66342 , as amended from time to time. Implementation of this chapter is meant to expand housing opportunities by increasing the number of smaller units available within existing neighborhoods while meeting Statewide housing goals and responding to wildfire and wastewater constraints.

• (b) The City recognizes opportunities to implement policies and programs of the Atascadero General Plan housing element providing for, and regulating, expanded housing opportunities for all persons within the community.

• (c) Implementation of this chapter is meant to expand housing opportunities for very low-, low- and moderate-income and/or elderly households by increasing the number of affordable by design and rental units available within existing neighborhoods.

• (d) As mandated in Sections 66314 and 66319 of the Government Code, units that comply with this chapter are considered not to exceed the density limits prescribed by the General Plan and/or this title from residential zoning districts.

• (Ord. 659 § 5, 2022; Ord. 682, 1/28/2025; Ord. 691, 1/27/2026)

As used in this chapter:

Accessory Dwelling Unit (ADU). ADUs are defined by Government Code Section 66313 to mean an attached or detached residential dwelling unit that provides complete independent living facilities for one or more persons and is located on a lot with a proposed or existing primary residence. ADUs shall include permanent provisions for living, sleeping, eating, cooking, and shall have a bathroom, and shall be located on the same parcel as the single family or multifamily dwelling per the standards set forth in this section. An accessory dwelling unit also includes an efficiency unit as defined in Section 17958.1 of the Health and Safety Code and a manufactured home as set forth in Section 18007 of the Health and Safety Code.

Existing Structure. For the purposes of this chapter and implementation of Government Code Section 66314 , an existing accessory structure or existing primary structure is defined as a structure, or the confines of a structure, that

has received a passed final inspection prior to January 1, 2020.

Guesthouse. Guesthouses are defined as residential occupancy construction (R) structures permitted prior to 2004 with a full bathroom, partial kitchen, and are the same as a residential dwelling unit for the purposes of defining use and calculating fees.

Junior Accessory Dwelling Unit (JADU). JADUs are defined by Government Code Section 66313 to mean a residential dwelling unit that is no more than 500 square feet in size and contained entirely within a single-family residence. A junior accessory dwelling unit may include separate sanitation facilities, or may share sanitation facilities with the existing structure. JADUs shall include permanent provisions for living and shall be located on the same parcel and within the same structure as the single-family dwelling. A JADU also includes an efficiency unit as defined in Section 17958.1 of the Health and Safety Code.

Livable Space. A space in a dwelling intended for human habitation, including living, sleeping, eating, cooking, or sanitation.

Primary Dwelling Unit. A primary dwelling unit (primary unit) is a principal or urban dwelling unit.

Principal Dwelling Unit. An existing or new proposed dwelling unit on a residential zoned legal lot of record permitted as allowed by the City's zoning and allowed density of the parcel and not constructed under the provisions for Chapter 5 or Chapter 18 of this title. Any additional existing units above the base residential density shall be considered an ADU or UDU. New units built as part of an SB9 lot split shall not be considered a principal dwelling unit if a principal unit already exists on the parent parcel or new parcel that is created from the lot split.

y of the parcel and not constructed under the provisions for Chapter 5 or Chapter 18 of this title. Any additional existing units above the base residential density shall be considered an ADU or UDU. New units built as part of an SB9 lot split shall not be considered a principal dwelling unit if a principal unit already exists on the parent parcel or new parcel that is created from the lot split.

Residential Multifamily Development. A residential multifamily property zoned for multiple principal dwelling units that has been developed with multi-family units as allowed by City zoning and which shares access, parking, and/or amenities regardless of the number of underlying parcels. This may include, but is not limited to, attached or detached residential units, common interest subdivisions, and related residential development on a single or multiple lots developed as a single development project with a developable density of at least 10 units per acre.

Residential Single-Family Property. A property zoned for single-family development with a base density of one dwelling unit per parcel.

Short-Term Rental. Short-term rentals (vacation rental) shall be defined as rental units with stays of 30 consecutive calendar days or less per individual or party.

Small-Lot Single-Family Subdivision. A subdivision with private side and rear yard areas built to a density of less than or equal to nine dwelling units per acre.

Urban Dwelling Unit (UDU). A primary dwelling unit established or proposed to be developed in accordance with the standards, procedures, and requirements set forth under Government Code Section 65852.21 and Title 9 , Chapter 18 of this code, either as a primary or secondary primary unit on a parcel. (Ord. 659 § 5, 2022; Ord. 682, 1/28/2025; Ord. 691, 1/27/2026)

• (a) Building Permit Required. A building permit application shall be required for the construction, occupancy, or conversion of any ADU or JADU.

• (b) Ministerial Review Process. An application for development of an ADU or JADU will be reviewed as a ministerial permit, without discretionary review or a hearing, if it meets all the requirements set forth in this section, does not impact environmental (including historic) resources, and after payment of all applicable submittal fees.

• (c) Garage Demolition. A demolition permit for a detached garage that is to be replaced with an ADU shall be reviewed with the application for the accessory dwelling unit and issued at the same time.

• (d) Water Service. All habitable dwelling units shall be served by a public water system.

• (e) Wastewater Service. To avoid health and safety impacts to ground water quality and nitrogen loading, ADUs shall be served by the City sanitary sewer system subject to one of the following exceptions:

  • (1) The parcel is three-quarters gross acres or greater and all of the following criteria can be met:

    • (i) It can be demonstrated that all properties within a one-quarter mile radius are of sufficient size, considering possible future lot splits and full development potential, to provide a minimum density of at least one-half acre per unit within the one-quarter mile radius.

    • (ii) It shall be demonstrated that a new or expanded on-site wastewater disposal system can accommodate the additional unit while meeting requirements of the City's Local Area Management Plan (LAMP).

  • (2) The parcel contains a gross lot area of one-half acres per unit or greater, including existing units and all units proposed at the time of application. For the purposes of this paragraph, "units" means all primary and accessory dwelling units, but shall not include Junior ADUs.

  • (3) ADUs that do not meet the above requirements and do not have the ability to connect to City sewer must be served by an on-site wastewater system that includes pre-treatment and shall be subject to the approval of the City Engineer. These systems must be approved and constructed in accordance with the City's LAMP standards.

• (f) Design. The design of an ADU and/or JADU shall be consistent with any objective design standards listed in this chapter.

• (g) Short-Term Rental Prohibited. ADUs and JADUs developed in accordance with Government Code Sections 66314 to 66339 shall not be rented for terms of less than 30 days.

• (h) Illegal Unit. The construction, establishment, or occupancy of an ADU and/or JADU that has not received a valid construction permit and is contrary to the provisions of this chapter is declared to be unlawful and shall constitute a misdemeanor and a public nuisance.

• (i) Agreement Required. Prior to issuance of a building permit for the ADU, the property owner shall submit to the City an agreement in a form approved by the Community Development Director, which shall run with the land and include at a minimum the following provisions:

• (1) A prohibition on the sale of the ADU separate from the sale of the principal dwelling unit, unless specifically authorized by State law or a subsequent lot split is approved and recorded.

  • (2) A restriction on the size and attributes of the ADU that conforms with Government Code Section 66314 .

  • (3) A prohibition on using the ADU as a short-term rental for periods of less than 30 days, as authorized by Government Code Section 66315 .

  • (4) Owner occupancy requirements for properties constructing or containing a JADU that shares sanitation facilities with the primary residence, as applicable.

  • (5) A statement that the restrictions shall be binding upon any successor owner of the property and that failure to comply with the restrictions shall result in legal action against the owner.

(Ord. 659 § 5, 2022; Ord. 682, 1/28/2025; Ord. 691, 1/27/2026)

• (a) Permitted Zoning Districts. Accessory and junior accessory dwelling units shall be allowed in all areas zoned to allow single-family or multifamily dwellings consistent with the standards of this section. ADUs shall not be allowed within the following locations:

  • (1) Pursuant to the authority provided by Section 65852.21(f) of the Government Code, no accessory dwelling unit or junior accessory dwelling unit shall be permitted on any lot in a single-family zoning district if: (i) an urban lot split has been approved pursuant to Title 11; and (ii) two units (primary dwelling unit, UDU, ADU, or JADU) already exist or are approved for construction.

  • (2) No ADUs shall be allowed inconsistent with the California Code of Regulations Title 14, Section 1273.08 .

  • (3) No ADU may be established in a commercial district unless all of the following conditions have been met:

    • (i) The ADU is part of an approved mixed-use development; and

    • (ii) The ADU is built above the ground floor.

  • (4) No ADU may be established on a lot subdivided pursuant to Government Code Section 66499.41 ("the Starter Home revitalization Act "), as amended from time to time.

(Ord. 659 § 5, 2022; Ord. 682, 1/28/2025; Ord. 691, 1/27/2026)

Standards for the development of accessory dwelling units (ADUs) shall be governed by this section. Each ADU shall be subject to compliance with the California Building Code and the following standards:

• (a) Maximum Floor Area. ADUs shall have a maximum floor area of 1,000 square feet, except as follows:

  • (1) A garage or other unconditioned space may be attached to an ADU provided any attached space with a nonR occupancy shall be limited to 300 square feet, or 500 square feet on lots one acre or greater. Any non-R occupancy space may be up to 500 square feet if it is on a different level than the ADU and used for vehicle parking and the entirety of the ADU is located on a different floor with the exception of an entry and stairs. If an existing accessory structure is converted to an ADU and the size of the unconditioned space exceeds the maximum limit, the existing space may remain but shall not be expanded.

  • (2) Properties may have a detached ADU up to 1,200 square feet when all of the following are met:

    • (i) The property is a minimum of one gross acre; and

    • (ii) The ADU height is limited to 18 feet; and

    • (iii) All other property development standards applicable to the zoning district shall apply, unless specifically modified by State law.

  • (3) Any dwelling unit other than the principal dwelling unit, that was established on the lot prior to the submittal of a complete application for a development pursuant to this chapter, may not be altered or expanded to a size greater than allowed by this chapter. No additional unconditioned space can be added if greater than the maximum allowances described in Section 9-5.050(a)(1) above. If existing units exceed the maximum size thresholds, no expansion or additions shall occur.

• (b) Required Parking. One off-street parking space (standard or tandem within a driveway) shall be required for each ADU, with the following exceptions:

  • (1) No parking shall be required if the ADU is within one-half mile walking distance of public transit.

  • (2) No parking shall be required when the ADU is within a designated historic district or on the site of a designated historic property.

  • (3) No parking shall be required when the ADU is part of a proposed or existing primary residence or a converted existing accessory structure.

  • (4) No parking shall be required when there is a car-share vehicle located within one block of the ADU.

  • (5) No parking shall be required when a permit application for an accessory dwelling unit is submitted concurrently with a permit application to create a new single-family dwelling or a new multifamily dwelling on the same lot, provided that the accessory dwelling unit and the parcel satisfy all other criteria listed in this chapter.

• (c) Replacement Parking. No replacement parking shall be required when a garage, carport, covered parking structure, or uncovered parking space is demolished in conjunction with the construction of an accessory dwelling unit or converted to an accessory dwelling unit.

• (d) Accessory Structure Conversion. ADUs may be constructed within existing accessory structures subject to the following:

  • (1) The size of the ADU shall comply with the size limitations set forth in Section 9-5.050(a) above.

  • (2) Any portions of the accessory structure not utilized for the ADU shall remain as non-habitable accessory space and shall be separated with a permanent wall from the interior space of the ADU. Any openings (doors) between the ADU and nonhabitable space shall comply with building and fire code standards.

  • (3) Conversions of existing legal accessory structures built prior to January 1, 2020, may be subject to different standards, consistent with Government Code Section 66323 .

• (e) Height. The maximum height of an ADU shall be as follows:

  • (1) 16 feet for any detached ADU where the setback is less than the minimum required setbacks for the underlying zoning district.

  • (2) 18 feet in a multifamily zone for any detached ADU where the setback is less than the required minimum setbacks for the zoning district if the multifamily dwelling on the same site is multi-story.

  • (3) 20 feet for any detached ADU that complies with the setbacks of the underlying zoning district.

  • (4) 25 feet for any detached ADU that complies with the setbacks of the underlying zoning district and where the footprint of the unit is located on a slope of 20% or greater.

  • (5) 25 feet for an ADU that is attached to a primary dwelling.

  • (6) No ADU shall exceed two stories.

• (f) Setbacks. An ADU shall maintain setbacks consistent with each zoning district and consistent with the California Building Code and Fire Code, unless reduced setbacks apply, consistent with Government Code Section 66314(d)(7) .

• (g) Building Separations. Minimum fire and building code separations shall be maintained between primary and secondary units.

• (h) Fire Sprinklers.

  • (1) An ADU shall comply with all applicable fire safety provisions of State law, as well as locally adopted building and fire codes under Title 4 , Chapter 7 , and Title 8 of this code.

  • (2) A detached ADU shall be required to be equipped with fire sprinklers unless the primary dwelling unit is not required to be sprinklered. The construction of an accessory dwelling unit shall not trigger a requirement for fire sprinklers to be installed in the existing primary dwelling.

• (i) Number of ADUs Permitted.

  • (1) Single-family zoned parcels and small-lot single-family subdivisions shall be allowed to construct accessory dwelling units consistent with Government Code Section 66323 and Section 9-5.060(c) of this chapter.

  • (2) Residential Multifamily/Mixed-Use Developments. ADUs shall be permitted in multifamily and mixed-use developments subject to the following:

    • (i) Portions of an existing multifamily building not used as livable space may be converted to one or more ADUs at a maximum ratio of 25% of the existing on-site units above the permitted site density.

• (ii) In addition to the units authorized by subsection (i )(2)(i) above, additional detached accessory dwelling units above the permitted site density shall be permitted within a multifamily or mixed-use development at the following quantities:

     - a. On a lot with an existing multifamily dwelling, eight detached accessory dwelling units, or a quantity equal to the number of existing dwelling units on the lot, whichever is fewer. 
  
     - b. On a lot with a proposed multifamily dwelling, not more than two detached accessory dwelling units. 
  
  - (iii) All residential units in a mixed-use development must meet the provisions of the underlying zoning district, except as provided for by Government Code Sections **66310** to **66342** , and must be consistent with all land use definitions for such development. 
  

• (j) Nothing in this section shall prohibit the construction of an ADU in accordance with Government Code Sections 66321(b)(3) , 66321(b)(4)(B) , 66321(b)(4)(C) , and 66323 . To the extent anything in this section conflicts with the provisions of the above-referenced Government Code sections, those Government Code sections shall control.

• (Ord. 659 § 5, 2022; Ord. 682, 1/28/2025; Ord. 691, 1/27/2026)

Standards for the development of junior accessory dwelling units (JADUs) shall be governed by this section. Each JADU shall be subject to compliance with the California Building Code and the following standards:

• (a) Maximum Floor Area. Each JADU shall be constructed within the walls of an existing or proposed primary dwelling unit and shall be a maximum of 500 square feet.

• (b) Septic Systems. JADUs may be served by the system serving an existing or proposed primary unit or a secondary septic system, subject to the approval of the City Engineer and provisions of the City's LAMP.

• (c) Number of JADUs Permitted. One JADU is permitted per single-family residential property or small-lot singlefamily residential subdivision parcel.

• (d) Design Standards.

  • (1) Each JADU may contain separate sanitation facilities or may share sanitation facilities with the principal dwelling unit.

  • (2) Each JADU shall include a separate entrance from the main entrance to the existing or proposed principal dwelling unit and may include an interior entry to the main living area.

  • (3) Each JADU shall, at a minimum, include an efficiency kitchen as defined by the building code and Government Code Section 66333(f)(1) .

• (e) Owner Occupancy. The property owner shall reside on site and maintain primary residency in either a primary dwelling unit, ADU, or the JADU if the JADU shares sanitation facilities with the primary residence.

• (f) Nothing in this section shall prohibit the construction of a JADU in accordance with Government Code Section 66323 . To the extent anything in this section conflicts with the provisions of Government Code Section 66323 , Section 66323 shall control.

• (Ord. 659 § 5, 2022; Ord. 682, 1/28/2025; Ord. 691, 1/27/2026)

Accessory units, whether attached or detached, shall be exempt from development impact fees when the gross floor area is less than 750 square feet. Units 750 square feet and larger shall be subject to the City's adopted development impact fee schedule.

(Ord. 659 § 5, 2022; Ord. 682, 1/28/2025; Ord. 691, 1/27/2026)