Contra Costa County Municipal Code § 82-24.018 Nonconforming units

Footnotes:

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Editor's note— Ord. No. 2025-07, § II, adopted May 13, 2025, amended Chapter 82-24 in its entirety to read as herein set out. Former Chapter 82-24, §§ 82-24.002—82-24.020, pertained to similar subject matter, and derived from Ord. No. 2020-01, § II, 1-21-20; and Ord. No. 2023-13, § II, 6-27-23.

The purposes of this chapter are to authorize accessory dwelling units and junior accessory dwelling units; to establish a procedure for reviewing and approving their development to ensure and maintain healthy and safe residential living environments; to establish location and development standards for accessory dwelling units; and to comply with State accessory dwelling unit law, commencing with Government Code Section 66310, which requires local agencies to consider applications for accessory dwelling unit permits ministerially without discretionary review or a public hearing.

(Ord. No. 2025-07, § II, 5-13-25)

For purposes of this chapter, the following words and phrases have the following meanings:

(a) "Accessory dwelling unit" has the meaning set forth in Government Code Section 66313(a).

(b) "Attached accessory dwelling unit" means an accessory dwelling unit attached to a primary dwelling unit.

(c) "Detached accessory dwelling unit" means an accessory dwelling unit detached from a primary dwelling unit.

(d) "Internal conversion" means the establishment of an accessory dwelling unit or junior accessory dwelling unit within an existing or proposed primary dwelling unit or within an existing accessory structure.

(e) "Junior accessory dwelling unit" has the meaning set forth in Government Code Section 66313(d).

(f) Whenever the term "residential second unit" is used in any ordinance, resolution, order, directive, or regulation of the county, it means "accessory dwelling unit."

(Ord. No. 2025-07, § II, 5-13-25)

(a) Except as otherwise provided in this section, an application for a permit to establish an accessory dwelling unit will be approved ministerially without discretionary review or public hearing if the accessory dwelling unit meets all of the following requirements: the location requirements specified in Section 82-24.010; the development standards specified in Section 82-24.012; and all applicable building standards in Title 7 of this Code and all applicable sewage and water requirements.

(b) An application for a permit to establish any of the following types of accessory dwelling units in a residential or mixed-use zoning district is not subject to the location requirements specified in Section 82-24.010 or the development standards specified in Section 82-24.012 and will be approved ministerially without discretionary review or public hearing.

(1) One internal conversion accessory dwelling unit and one internal conversion junior accessory dwelling unit on a lot with a proposed or existing single-family dwelling, if:

(A) Each internal conversion has independent exterior access;

(B) All side and rear setbacks are sufficient for fire safety; and

(C) Each internal conversion meets all applicable building standards in Title 7 of this Code and all applicable sewage and water requirements.

If an internal conversion is a junior accessory dwelling unit, it must comply with the requirements of Government Code section 66313. All internal conversions in an existing structure authorized under this subsection (b)(1) may include a total expansion of not more than one hundred fifty square feet beyond the physical dimensions of the existing structure in which the conversions are located, but the expansions must be limited to accommodating ingress and egress.

(2) One detached, new construction, accessory dwelling unit on a lot with a proposed or existing single-family dwelling, if: the side and rear setbacks are a minimum of four feet; the detached accessory dwelling unit does not exceed eight hundred square feet in size; the detached accessory dwelling unit does not exceed the applicable height limitations specified in Government Code section 66321(b)(4); and the detached accessory dwelling unit meets all applicable building standards in Title 7 of this Code and all applicable sewage and water requirements. The detached accessory dwelling unit may be combined with a junior accessory dwelling unit authorized under subsection (b)(1).

(3) One or more accessory dwelling units that are internal conversions within the non-livable space of an existing multiple-family dwelling, including but not limited to storage rooms, boiler rooms, passageways, attics, basement, or garages. Each internal conversion under this subsection (b)(3) must meet all applicable building standards in Title 7 of this Code and all applicable sewage and water requirements. The number of internal conversions authorized within an existing multiple-family dwelling under this subsection (b)(3) may not exceed twenty-five percent of the number of existing multiple-family units in the dwelling.

(4) One or more detached accessory dwelling units on a lot with a proposed or existing multiple-family dwelling, if:

(A) All side and rear setbacks are a minimum of four feet;

(B) Each detached accessory dwelling unit does not exceed the applicable height limitations specified in Government Code section 66321(b)(4); and

(C) Each detached accessory dwelling unit meets all applicable building standards in Title 7 of this Code and all applicable sewage and water requirements.

The number of detached accessory dwelling units permitted on a lot with an existing multiple-family dwelling under this subsection (b)(4) may not exceed the number of existing units on the lot or eight detached accessory dwelling units, whichever is less. The number of detached accessory dwelling units permitted on a lot with a proposed multiple-family dwelling under this subsection (b)(4) may not exceed two detached accessory dwelling units.

(Ord. No. 2025-07, § II, 5-13-25)

(a) An application for an accessory dwelling unit permit must be submitted to the Department of Conservation and Development before a building permit application is submitted to the county. An application for a junior accessory dwelling unit permit must be submitted in the same manner and form as an application for an accessory dwelling unit permit.

(b) An application for an accessory dwelling unit permit must be made in writing and contain the following information:

(1) Name(s) and address(es) of applicant(s) and property owner(s).

(2) Size, indicating dimensions and square footage of the primary dwelling unit and the proposed accessory dwelling unit.

(3) A legible scale drawing, showing:

(A) A north arrow to indicate lot orientation.

(B) Lot dimensions and labels for all property lines.

(C) Siting and location of the primary dwelling unit and the proposed accessory dwelling unit.

(D) Floor plan configuration of the primary dwelling unit and the proposed accessory dwelling unit.

(E) All other existing and proposed buildings, structures, and improvements, including retaining walls, fencing, driveways, and parking areas. All buildings and structures must be labeled.

(F) Location and dimensions of any additional off-street parking provided to serve the proposed accessory dwelling unit.

(G) For detached accessory dwelling units, elevations of the proposed unit showing exterior features and dimensions, including maximum building height. "Exterior features" include entrances, windows, and roof.

(4) Location and description of water and sanitary services for both the primary dwelling unit and the proposed accessory dwelling unit.

(5) A written legal description of the property.

(Ord. No. 2025-07, § II, 5-13-25)

(a) Accessory dwelling units that comply with this chapter may be located on any lot in a single-family residential district (R-6, R-7, R-10, R-12, R-15, R-20, R-40, R-65, and R- 100), a water recreation district (F-1), planned unit district (P-1) for residential uses, or a multiple-family residential district (M-6, M-9, M-12, M-17, and M-29).

(b) Accessory dwelling units that comply with this chapter may be located on any lot in an agricultural district (A-2, A-3, A-4, A-20, A-40, and A-80). If accessory dwelling units are proposed for a lot under a Williamson Act contract, the accessory dwelling units will be allowed subject to the provisions of this chapter unless the Williamson Act contract prohibits an accessory dwelling unit or a residential second unit on the property.

(c) No subdivision rights are authorized that would result in an accessory dwelling unit being located on a separate lot.

(Ord. No. 2025-07, § II, 5-13-25)

(a) Accessory Dwelling Unit Size.

(1) A detached accessory dwelling unit may not exceed the following sizes.

(A) A detached accessory dwelling unit may not exceed one thousand square feet in any zoning district where an accessory dwelling unit is allowed, unless the accessory dwelling unit is located on a lot of twelve thousand square feet or more, or in an agricultural district, or in the Kensington (-K) combining district.

(B) A detached accessory dwelling unit may not exceed one thousand two hundred square feet on a lot of twelve thousand square feet or more.

(C) A detached accessory dwelling unit may not exceed one thousand two hundred square feet in an agricultural district.

(D) In the Kensington (-K) combining district, a detached accessory dwelling unit may not exceed eight hundred fifty square feet if the accessory dwelling unit provides one bedroom and may not exceed one thousand square feet if the accessory dwelling unit provides more than one bedroom.

(2) An attached accessory dwelling unit may not exceed the following sizes.

(A) Except as otherwise provided in subsection (B) below, an attached accessory dwelling unit may not exceed the sizes specified in this subsection (A).

(i) An attached accessory dwelling unit may not exceed one thousand square feet in any zoning district where an accessory dwelling unit is allowed, unless the accessory dwelling unit is located on a lot of twelve thousand square feet or more, or in an agricultural district, or in the Kensington (-K) combining district.

(ii) An attached accessory dwelling unit may not exceed one thousand two hundred square feet on a lot of twelve thousand square feet or more.

(iii) An attached accessory dwelling unit may not exceed one thousand two hundred square feet in an agricultural district.

(iv) In the Kensington (-K) combining district, an attached accessory dwelling unit may not exceed eight hundred fifty square feet if the accessory dwelling unit provides one bedroom and may not exceed one thousand square feet if the accessory dwelling unit provides more than one bedroom.

(B) An attached accessory dwelling unit may not exceed fifty percent of the living area of the primary dwelling unit to which the accessory dwelling unit is attached, except that an attached accessory dwelling unit may exceed fifty percent of the living area of the primary dwelling unit to the extent necessary to permit an accessory dwelling unit of eight hundred fifty square feet if the accessory dwelling unit provides one bedroom or one thousand square feet if the accessory dwelling unit provides more than one bedroom.

(b) Living Provisions. An accessory dwelling unit must provide complete independent living facilities for one or more persons, including permanent provisions for living, sleeping, eating, cooking, and sanitation.

(c) Permanent Foundation. A permanent foundation is required for all accessory dwelling units.

(d) Sewage and Water. If a private sewage disposal system, water system, or both are proposed to be used, it must meet all applicable county regulations and be approved by the health officer before an accessory dwelling unit may be established. Verification that the standard has been met is required prior to final inspection.

(e) Independent Exterior Access. An accessory dwelling unit must have independent exterior access separate from that of the primary dwelling unit. The independent exterior access must be located on the building side or building rear, or not visible from the street.

(f) Types of Accessory Dwelling Units. An accessory dwelling unit may be attached to a primary dwelling unit or detached from a primary dwelling unit.

(1) If an accessory dwelling unit is attached to a primary dwelling unit, the accessory dwelling unit must be an internal conversion of an attached garage or other area within the primary dwelling unit, or an addition to the primary dwelling unit.

(2) If an accessory dwelling unit is detached from a primary dwelling unit, the accessory dwelling unit must be an internal conversion of a detached garage or other accessory building, or new construction. A detached accessory dwelling unit must be located on the same lot as the primary dwelling unit.

(g) Garage Attached to a Detached Accessory Dwelling Unit. If a garage is attached to a detached accessory dwelling unit, the garage may not exceed the following sizes:

(1) Five hundred square feet on lots of twenty thousand square feet or less in all zoning districts where an accessory dwelling unit is allowed, except in an agricultural district.

(2) Six hundred square feet on lots larger than twenty thousand square feet and smaller than five acres in all zoning districts where an accessory dwelling unit is allowed, except in an agricultural district.

(3) Eight hundred square feet on lots of five acres or more.

(4) Eight hundred square feet in an agricultural district.

(h) Yards and Building Height.

(1) An accessory dwelling unit must comply with all requirements relating to yards (front setbacks, side, and rear) and building height that are generally applicable to residential construction in the zone in which the property is located, except as otherwise provided in this subsection (h).

(2) A setback is not required for an accessory dwelling unit that is an internal conversion or that is constructed in the same location and to the same dimensions as an existing building.

(3) A setback of four feet from the side and rear lot lines is required for an accessory dwelling unit that is not an internal conversion and is not constructed in the same location and to the same dimensions as an existing building.

(4) An accessory dwelling unit and any portion of an accessory dwelling unit is subject to the applicable height limitations specified in Government Code section 66321(b)(4) if it is located:

(A) Within a front, back, or side yard area applicable to residential construction in the zone in which the lot is located; or

(B) In the Kensington (-K) combining district.

(i) Off-Street Parking.

(1) A lot containing an accessory dwelling unit must provide an additional off-street parking space to serve the accessory dwelling unit, except as otherwise provided in this subsection (i). The additional space may be within a setback area or in tandem, unless specific findings are made that parking in a setback area or in tandem is not feasible based on site or regional topographical or fire and life safety conditions.

(2) Replacement parking spaces are not required if a garage, carport, covered parking structure, or uncovered parking space that provides off-street parking is demolished or converted in conjunction with the construction of an accessory dwelling unit.

(3) No additional off-street parking is required for an accessory dwelling unit in any of the following instances:

(A) The accessory dwelling unit is located within one-half mile walking distance of public transit.

(B) The accessory dwelling unit is located within an architecturally and historically significant historic district.

(C) The accessory dwelling unit is an internal conversion.

(D) The accessory dwelling unit is located within a permit-parking area designated pursuant to Chapter 46-10, but an on-street parking permit is not available under that chapter to the occupant of the accessory dwelling unit.

(E) A car share vehicle pick-up location is within one block of the accessory dwelling unit. A "car share vehicle" has the same meaning as in Vehicle Code Section 22507.1.

(F) An application for the accessory dwelling unit is submitted with an application for a proposed single-family dwelling or a proposed multiple- family dwelling on the same lot, and the accessory dwelling unit or lot satisfies any other criteria listed in this subsection (i)(3).

(Ord. No. 2025-07, § II, 5-13-25)

(a) No accessory dwelling unit or junior accessory dwelling unit may be rented or offered for rent for a term of less than thirty days.

(b) A junior accessory dwelling unit may not be sold separately from the primary single- family dwelling.

(c) An accessory dwelling unit may not be sold separately, except in conformance with Government Code section 66341.

(Ord. No. 2025-07, § II, 5-13-25)

Before obtaining a permit authorizing the establishment of a junior accessory dwelling unit, the applicant shall do the following:

(a) Enter into an agreement of restrictions with the county that provides the following:

(1) The junior accessory dwelling unit shall not be sold separately from the primary single-family dwelling.

(2) The junior accessory dwelling unit is restricted to the maximum size allowed under the permit and must comply with all permit restrictions and requirements.

(3) The restrictions are binding upon any successor in ownership of the property and lack of compliance may result in legal action by the county against the property owner.

(b) Record the agreement with the county recorder.

(c) Prepare a disclosure statement that shall be included in any future offer or sale documents. The statement shall read as follows:

"You are purchasing a property with a permit for a junior accessory dwelling unit. This permit carries with it certain restrictions that must be met by the owner of the property. You are prohibited from selling the junior accessory dwelling unit separately from the primary single-family dwelling. The junior accessory dwelling unit is restricted to the maximum size allowed under the permit and must comply with all permit restrictions and requirements. The junior accessory dwelling unit may not be rented or offered for rent for a term of less than thirty days. The permit is available from the current owner or from the Contra Costa County Department of Conservation and Development."

(Ord. No. 2025-07, § II, 5-13-25)

Notwithstanding the provisions of Section 82-8.006 of this Code, if the existing primary dwelling unit is a legal nonconforming unit, an accessory dwelling unit or junior accessory dwelling unit may be constructed only if the nonconformity is not expanded and the accessory dwelling unit or junior accessory dwelling unit meets all current applicable zoning and building standards.

(Ord. No. 2025-07, § II, 5-13-25)

(a) Notwithstanding anything in this chapter to the contrary, an application to permit an unpermitted accessory dwelling unit or unpermitted junior accessory dwelling unit that was constructed before January 1, 2020, shall be approved ministerially without discretionary review or public hearing in accordance with Government Code section 66332, unless the county building official, or designee, finds that the criteria in both subsection (a)(1) and subsection (a)(2) are met.

(1) The unpermitted accessory dwelling unit or unpermitted junior accessory dwelling unit violates:

(A) The building standards set forth in Article 1 (commencing with Section 17960) of Chapter 5 of Part 1.5 of Division 13 of the Health and Safety Code;

(B) The State accessory dwelling unit law pursuant to Article 2 (commencing with Section 66314) or Article 3 (commencing with Section 66333) of Chapter 13 of Division 1 of Title 7 of the Government Code, as applicable; or

(C) This chapter.

(2) It is necessary to correct the violation specified subsection (a)(1) to comply with the standards specified in Health and Safety Code section 17920.3.

(b) This section does not apply to a building that the county building official has deemed substandard pursuant to Health and Safety Code section 17920.3.

(Ord. No. 2025-07, § II, 5-13-25)

Fees for accessory dwelling unit permits and junior accessory dwelling unit permits will be in amounts established by the board of supervisors in the Department of Conservation and Development's fee schedule. To the extent permitted by state law, accessory dwelling units and junior accessory dwelling units are subject to all applicable fees for new development.

(Ord. No. 2025-07, § II, 5-13-25)