Building an ADU in Costa Mesa
Costa Mesa is one of the more flexible Orange County cities for ADUs, and the city says its rules don’t require any parking for an ADU at all. That makes a lot of smaller lots workable. Lamarc Prime Builders helps Costa Mesa homeowners add a detached ADU, an addition, or a garage conversion for rental income, family, or a home office. We plan around the city’s specifics, including its objective design standards for second-story ADUs, its limits on exterior stairs and balconies, and the 6 ft separation from your main house. We take care of design, permits, and construction.
ADU Services Available in Costa Mesa, CA
ADU projects in Costa Mesa often require careful planning around lot layout, access, and utilities. We work with homeowners to identify constraints early and design an ADU that fits the property while staying compliant with city requirements.
✅ Detached & Attached ADUs
✅ Garage Conversion ADUs
✅ Junior ADUs (JADUs)
✅ ADU Planning & Design Coordination
✅ Permits, Plan Submittals & City Revisions
✅ Construction, Inspections & Final Completion
Start with a free site evaluation to understand your options and plan the next steps with confidence.
ADU Rules in Costa Mesa
ADUs allowed per lot
1 ADU + 1 JADU on a single-family lot
Max detached ADU size
Up to 1,200 sq ft
Max attached ADU size
Greater of 1,000 sq ft or 50% of the home, capped at 50% of the home's floor area
Max JADU size
Up to 500 sq ft
Max height (detached)
18 ft
Two-story ADU
Allowed with conditions: 25 ft from the front line, hidden stairs, no roof decks
Setbacks
4 ft side and rear
Space between buildings
6 ft between a detached ADU and the main house
Parking
None required
Owner occupancy
Not required for an ADU; JADU requires the owner to live on site
Short-term rental (Airbnb)
Short-term rentals under 31 days prohibited
Impact fees
Apply at 750 sq ft or more, proportional to the main home; JADU has its own fee
Pre-approved plans
We check for city-approved plans for your property
Permit review
Standard plan check (no over-the-counter permits); consult Planning first
Approval timeline
60 days after a complete application (state law)
Local insight
Costa Mesa doesn't require parking for an ADU, but second-story ADUs have strict standards, including a 25 ft setback from the front, hidden stairs, and no roof decks.
How ADU Permitting Works in Costa Mesa
Costa Mesa doesn’t issue ADU permits over the counter. Every ADU goes through standard plan check, and the city recommends you consult a planner before you submit. Each ADU and JADU gets its own address from the city. Fire sprinklers are required only if the main home has them.
Planning questions go to the Planning Division at 77 Fair Drive, (714) 754-5245, or planninginfo@costamesaca.gov.
Property feasibility review
Review zoning, lot conditions, access, utilities, and applicable ADU requirements.
ADU design and preparation
Prepare the site plan, architectural drawings, engineering, and required supporting documents.
City plan review and approvals
Submit the application, coordinate with city departments, and respond to plan-check corrections.
Permit issuance and construction
After approval and permit issuance, proceed with construction and required inspections.
FAQs About ADUs in Costa Mesa
Does Costa Mesa issue ADU permits over the counter?
No. Every ADU goes through standard plan check, and the city recommends you consult a planner before you submit. Planning questions go to the Planning Division at 77 Fair Drive, (714) 754-5245. We handle the pre-submittal conversation and the submittal for you.
Can I use pre-approved plans in Costa Mesa?
Most Costa Mesa ADUs start with a custom design built around your lot and the city’s standards. If a city-approved plan fits your property, we’ll tell you up front.
What documents are required to submit an ADU permit application in Costa Mesa?
You submit a full plan set for standard plan check, and each ADU and JADU is assigned its own address by the city. Before your permit is issued, the city records a deed restriction that prohibits short-term rentals. We prepare the package and coordinate with the city.
Can I convert an existing garage into an ADU in Costa Mesa?
Yes, and replacement parking is optional. If the garage door faces the street, the city requires it to be covered with landscaping and openings that match your home’s design.
How can Lamarc Prime Builders help with ADU design, permitting, and construction in Costa Mesa?
We handle the whole project in one place. We start with a feasibility review of your lot, prepare the design, drawings, and engineering, submit to Costa Mesa’s Planning and Building divisions and respond to plan-check corrections, and then build your ADU through final inspections.
