ADUByCity
Verified March 14, 2026

ADU Regulations in Costa Mesa, California

Orange County · CA · Pop. 115,000

Max ADU Size

1,200

sq ft detached

Rear Setback

4 ft

Permit Timeline

60 days

Build Cost

$175,000 – $360,000

Zoning

Allowed ADU Types

✓Detached ADU
✓Attached ADU
✓JADU (Junior ADU)
✓Garage Conversion
Max per lot: 2 ADUs✓ No owner-occupancy required

State law preempts local owner-occupancy requirements. JADUs allowed within existing single-family home footprint. Costa Mesa is adjacent to Newport Beach and South Coast Plaza, driving strong professional renter demand throughout the city.

Source: City of Costa Mesa — Accessory Dwelling Units · Costa Mesa Municipal Code Title 13 (Zoning)

Dimensions

Size & Setback Requirements

Detached

1,200

sq ft max

JADU

500

sq ft max

Attached

50% of primary home, max 1,200 sq ft

Setbacks

front

Same as primary dwelling

side

4 ft

rear

4 ft

Max height: 16 ft (detached); 25 ft or height of primary structure if attached

Lot coverage: Per underlying zone; detached ADUs on lots under 10,000 sq ft may reach up to 60%

Existing structures converted to ADUs must meet 4 ft side/rear setbacks or may use existing nonconforming setbacks where applicable.

Permitting

Permit Process

Department

Costa Mesa Development Services — Planning Division

Review Timeline

60 days

Permit Fees

$9,000 – $18,000

Impact Fees

Impact fees waived for ADUs under 750 sq ft; proportional fees apply above that threshold

Required Documents

  • ›Site plan (to scale)
  • ›Floor plans
  • ›Elevations
  • ›Title 24 energy compliance (CalGreen)
  • ›Structural drawings
  • ›Grading/drainage plan if applicable

Orange County is served by OCSD for sewer; connection fees assessed separately. Ministerial review only — no discretionary approval required.

Visit Costa Mesa Development Services — Planning Division →

Infrastructure

Utilities & Requirements

Solar

Required

Parking

Not required

Separate Meter

Optional

Fire Sprinklers

See note

Sewer: Connection to Orange County Sanitation District (OCSD) system required; lateral connection fee applies
Fire Sprinklers: Not required unless primary structure requires them
Parking: No additional parking required

Financials

ADU Costs in Costa Mesa

Typical Build Cost

$175,000 – $360,000

Cost per Sq Ft

$245 – $320

Monthly Rental

$2,000 – $3,200/mo/mo

Property Value Added

Adds $250,000 – $450,000 to property value in strong OC market

Available Grants & Programs

  • ★CalHFA ADU Grant Program available (up to $40,000 pre-development)
  • ★Orange County Housing Finance Trust programs may apply

South Coast Plaza employment hub and Newport Beach proximity sustain high rental demand. Studio and 1-bed ADUs near the 405/55 interchange typically lease within 2 weeks.

Use the free ADU Cost Calculator →

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Disclaimer: Information is compiled from publicly available municipal codes for general informational purposes only. It does not constitute legal, zoning, or construction advice. Regulations change frequently. Always verify with your local planning department. Last verified: March 14, 2026. Verify with Costa Mesa Development Services — Planning Division

Explore More

Nearby Cities in Orange County

Anaheim

Max 1,200 sq ft · $140,000 – $300,000

Santa Ana

Max 1,200 sq ft · $120,000 – $260,000

Irvine

Max 1,200 sq ft · $160,000 – $340,000

Huntington Beach

Max 1,200 sq ft · $175,000 – $380,000

Garden Grove

Max 1,200 sq ft · $160,000 – $330,000

Fullerton

Max 1,200 sq ft · $160,000 – $330,000

Costa Mesa Quick Facts

  • Max size1,200 sq ft
  • Rear setback4 ft
  • Permit timeline60 days
  • Build cost$175,000 – $360,000
  • Rental income$2,000 – $3,200/mo/mo
  • Owner occupancyNot required

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Official Source

City of Costa Mesa — Accessory Dwelling Units

Costa Mesa Municipal Code Title 13 (Zoning)

Last verified: March 14, 2026

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