Costa Mesa, CA Accessory Structures: Garage Conversions (2026)

Under Sec. 13-35(12), when a garage becomes an ADU and the converted facade is visible from a public right-of-way, the city recommends the wall be covered with landscaping over at least 50% of its area, or that the facade include openings equal to at least 10% of the wall, with at least one door meeting the entry standards of subsection (13) or a window matching the residence's existing windows in material and design. These are labeled 'recommended,' giving applicants design flexibility during plan check rather than an automatic rejection for noncompliance.

Subsection (13) is mandatory: if the driveway leading to the converted garage is removed, it must be replaced with landscaping or open space, and the curb cut and driveway apron must be removed and replaced with a standard curb, gutter, and parkway to city standards. 5 feet wide by 18 feet long. Owners do not have to replace the lost garage parking space itself; Sec. 13-35(15)(b) confirms that converting or demolishing a parking structure for an ADU does not trigger a requirement to replace those off-street spaces elsewhere on the lot, and the driveway does not lose its legal status even after the garage behind it is gone.

The Economic and Development Services Department reviews ADU applications, and Sec. 13-35(16) bars the city from conditioning ADU permit approval on correcting unrelated nonconforming development standards on the property. ADUs built by converting a garage over 800 square feet still trigger the open space and landscaping standards of Sec. 13-32 and Sec. 13-106.