Costa Mesa has more permissive ADU rules than the state baseline in several areas — a 150 sq ft minimum unit size, optional parking, and a Safe ADU Legalization Program for non-conforming units.
City highlights a 150 sq ft minimum unit size. Objective design standards include second-floor/two-story setbacks as local differentiators.
State guarantee: California requires every city to allow at least an 800 sq ft ADU exempt from local lot coverage, FAR, and front-setback rules.
Height baseline: 16 ft for detached, rising to 18 ft within ½ mile of major transit. Attached ADUs follow the primary home, capped at 25 ft.
Parking is optional under the city's ADU ordinance summary.
Planning Division contact (714) 754-5245. Links to Pre-Engineered/Pre-Approved ADU program and Safe ADU Legalization Program subpages.
State backstop: A complete ADU permit must receive a decision in 60 business days. If the city stalls past 30 business days, AB 253 lets you hire a certified private plan checker to force a 10-business-day decision.
Fee waivers/deferrals not stated on the main ADU page. Verify with Planning. Hub references CalHFA and OC Housing Finance Trust state grants.
SB 543: No impact fees on ADUs ≤750 sq ft. Above 750 sq ft, fees scale to the ratio of ADU size vs the main home.
Visit the official Costa Mesa ADU page (link in hero) for current eligibility and downloads.
Standard ADUs in Costa Mesa: no owner-occupancy required (made permanent in 2023).
JADUs: limited to 500 sq ft of interior livable space within an existing single-family home. Owner occupancy is required only when sanitation facilities are shared with the main house. JADUs cannot be used as short-term rentals (AB 1154 / SB 543).
Sketch a floorplan, walk through it in 3D, and have our planners review it for size, height, and setback compliance before you submit to Costa Mesa.
Heads up: Local rules change frequently. This page summarizes publicly available state law (California Government Code §§ 66310–66342) and current local guidance for general planning purposes. Always confirm specifics with the Costa Mesa planning desk before submitting plans. ADUMetrics does not provide legal advice.