Accessory Structures in Costa Mesa, CA (2026)
5 verified accessory structures rules for Costa Mesa, California, sourced directly from the municipal code and official government pages.
Verified from official government sources
ADU Rules
Costa Mesa approves accessory dwelling units ministerially, without a public hearing, on any single-family or multifamily lot that keeps its existing home under Municipal Code § 13-35. A single-family lot may add one detached ADU up to 1,200 square feet plus a Junior ADU, while multifamily lots may add units equal to 25% of existing units or as many as eight detached ADUs.
Costa Mesa Accessory Dwelling Unit Zoning Rules
Some RestrictionsCosta Mesa, CA, Municipal Code § 13-35(b)(1), (3), (5)
(b) Accessory dwelling units. (1) Residential and mixed use zones only. ADUs are permitted in single-family, multifamily, mixed-use zones (i.e., zones where single-family and/or multifamily dwellings are allowed), and within approved master plan sites with residential uses in other zones, and only on a legal lot with proposed or existing residential dwelling(s) which will remain on site. ... (3...
ADU Owner Occupancy
Costa Mesa requires the owner of a lot with a Junior ADU to live in either the primary home or the Junior ADU as a primary residence under Municipal Code § 13-35(c)(3). Standard ADUs carry no such owner-occupancy requirement; only Junior ADUs trigger it, with an exception for government agencies, land trusts, and housing organizations.
Costa Mesa Junior ADU Owner Occupancy Rule
Some RestrictionsCosta Mesa, CA, Municipal Code § 13-35(c)(3)
(3) Owner occupancy requirement. The owner of a parcel proposed for a Junior ADU shall occupy as a primary residence either the primary dwelling unit or the Junior ADU. Owner-occupancy is not required if the owner is a governmental agency, land trust, or "housing organization" as that term is defined in Government Code section 65589.5(k)(2), as that section may be amended from time to time.
ADU Rental Restrictions
Costa Mesa bars renting an accessory dwelling unit for less than 31 days under Municipal Code § 13-35(b)(8), and the same 31-day floor applies to Junior ADUs under § 13-35(c)(4). The rule closes off short-term vacation rental use of both ADU types citywide, regardless of zone.
Costa Mesa ADU Short-Term Rental Ban
Significant RestrictionsCosta Mesa, CA, Municipal Code § 13-35(b)(8) and § 13-35(c)(4)
(8) Short-term rentals prohibited. An ADU shall not be rented for periods of less than 31 days. ... (4) Short-term rentals prohibited. A Junior ADU shall not be rented for periods of less than 31 days unless otherwise authorized by the municipal code.
Shed & Carport Rules
Costa Mesa reviews any accessory building or shed built within 75 feet of the front property line, or on the front half of the lot, for screening and compatibility with the main house under Municipal Code § 13-33. Shipping containers are flatly prohibited in residential zones, while underground structures like fallout shelters are allowed anywhere below grade.
Costa Mesa Accessory Building and Shed Rules
Some RestrictionsCosta Mesa, CA, Municipal Code § 13-33 (Accessory Buildings and Structures)
§ 13-33. Accessory buildings and structures. (a) Accessory buildings or structures constructed closer than 75 feet from the front property line or on the front one-half (½) of the lot, whichever is less, shall be reviewed by the planning division for adequate screening and compatibility with the main structure. (b) Underground structures including fallout shelters shall be allowed to be const...
Garage Conversions
Costa Mesa lets homeowners convert an attached or detached garage into an accessory dwelling unit, but Municipal Code Sec. 13-35(12)-(13) attaches design and driveway conditions. A converted garage facing a public street needs a landscaped or windowed facade, and any removed driveway must be replaced with landscaping, not left as bare concrete.
Costa Mesa Garage-to-ADU Conversion Rules
Some RestrictionsCosta Mesa Municipal Code Sec. 13-35(12)-(13)
Recommended garage conversion design considerations. Blank facade. When a garage is converted to an ADU, if the facade of the converted garage is visible from a public right-of-way, the following design considerations are recommended: Be covered with landscaping that covers at least 50% of the wall, or Include openings of at least 10% of the facade with at least one door that complies with sect...
Looking for Orange County county-wide rules?
County ordinances apply to unincorporated areas and may supplement Costa Mesa city rules.
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