City ADU planning guide

Costa Mesa ADU regulations and next steps

Start with the most important planning decisions, then review the detailed city rules below before choosing a detached ADU plan or requesting a property-specific feasibility review.

Costa Mesa ADU rules overview

Detailed local requirements vary by property. Use this section as a starting point for setbacks, parking, height, utilities, and approval considerations.

Lot fit

Setbacks and buildable area

Start with rear and side setbacks, lot coverage, access, and where a detached ADU can realistically sit on the property.

Design limits

Size, height, and unit type

Check whether the property is better suited for a detached ADU, attached ADU, garage conversion, or junior ADU.

Approvals

Parking, utilities, and permits

Confirm parking exemptions, utility connection requirements, impact fees, and city review steps before finalizing plans.

Key Points:

  • Types of ADUs Costa Mesa allows attached, detached, and junior ADUs.
  • Lot Size No minimum lot size requirement.
  • Size Limits
    • Detached ADU: Maximum of 1,200 square feet.
    • Attached ADU: Maximum of 50% of the primary residence's floor area.
    • Junior ADU: Minimum size of 150 square feet.
  • Setbacks
    • Detached ADU: 4-foot side and rear setbacks.
    • Attached and Junior ADUs: Sufficient setback to ensure fire safety.
  • Parking
    • Detached ADU: One off-street parking space required, unless exempt.
    • Attached and Junior ADUs: No additional parking required if existing parking is available.
  • Design Standards
    • Must be compatible with the primary residence and neighborhood character.
    • Objective design standards, such as second-floor/two-story setbacks.
  • Permitting Process
    • Pre-application meeting recommended.
    • Submittal of plans and required documentation.
    • Review and approval process by the City.
    • Building permit issuance.
    • Construction and final inspection.

Additional Considerations:

  • Multi-family Properties Rules for ADUs on multi-family properties may vary.
  • Historical Districts Additional design guidelines and review processes may apply.
  • Coastal Zone
    • If your property is in a coastal zone, specific regulations may apply.
  • Utility Hookups Coordinate with utility providers for water, sewer, and electrical service.

Helpful Resource:

  • City of Costa Mesa Planning Department Contact them directly for the most accurate and up-to-date information.
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