What's the same in every OC city
California state law sets a floor no city can go below: ministerial (no-hearing) review, a 60-day decision clock on complete applications, at least an 800 sq ft ADU with 4-foot side and rear setbacks, and size minimums of 850 sq ft (studio/1-bed) or 1,000 sq ft (2+ bed) that local caps can't undercut. Our California ADU laws guide covers the statewide framework, and the size & setback calculator shows the exact floors for your ADU type.
Everything beyond that floor is local — and that's where OC cities genuinely differ.
Where OC cities differ
Highlights from our city research — each links to the full city guide with sources and details:
| City | What stands out |
|---|---|
| Anaheim | Express Program offers one-day permitting and zero design costs for qualifying ADUs. |
| Fullerton | Allows two-story detached ADUs up to 30 feet — among the most generous height allowances in our OC coverage. |
| Santa Ana | Allows two-story detached ADUs up to 20 feet — more vertical room than many neighboring cities. |
| Brea | A builder-submitted pre-approved plan model (designers get their own plans pre-approved), plus hillside fuel-modification wildfire rules. |
| La Habra | Updated its ADU ordinance in July 2025 and accepts the County of San Diego's pre-approved plans — used unmodified. |
| Huntington Beach | Rental restrictions plus Coastal Zone rules — two layers many inland cities don't have. |
| San Clemente | Requires evidence of Coastal Commission approval as part of the submittal packet for Coastal Zone ADUs. |
| Costa Mesa | Runs a Safe ADU Legalization Program for existing unpermitted units. |
| Fountain Valley | Owner-occupancy required for ADUs built after January 2025, plus a 30-day minimum rental period. |
| Seal Beach | Requires 6 feet of separation between a detached ADU and the primary home — more than the 4-foot setback common elsewhere. |
| Orange | Ties conversion-ADU size to your existing structure's footprint. |
| Laguna Niguel | PAADU pre-approved design program intended to speed up permitting. |
| Newport Beach | Over 63% of the city is in the Coastal Zone, so a Coastal Development Permit is common; an 800 sq ft override protects small lots and a recorded deed restriction (no short-term rentals, no separate sale) is required before permit. |
| San Juan Capistrano | Solar on new detached ADUs is enforced at final inspection, fire sprinklers track the main house, a Santa Margarita Water District sanitation clearance is required, and ADU-permit units face a 35% lot-coverage cap. |
| Westminster | ADU applications get reviewed by three separate city divisions — worth planning around. |
All 23 Orange County city guides
Before you start in any OC city
- Confirm your jurisdiction. Some addresses are unincorporated county, not the city they share a name with — different rules apply. Our zoning lookup guide shows how to check.
- Check for a pre-approved plan program. Where one exists, it can meaningfully shorten design and permitting — see the table above for cities that offer one, and our statewide pre-approved plans guide for how the AB 1332 pathway works.
- Ask about fees below 750 sq ft. Development impact fees are exempt at 750 sq ft or less statewide — our fee guide has the thresholds.
- Get the local answer in writing. City counter staff answers vary; the municipal code and your permit record are what count.
How this page is built: every city-specific claim above is drawn from our individual city guides, each researched from that city's official planning resources and municipal code, with state-law context from the California HCD ADU framework. City programs and ordinances change — the linked city guide is always the more detailed reference, and your city's planning department is the final authority. This page is general information, not legal advice, and doesn't guarantee what your specific property qualifies for. See also our Inland Empire ADU guide.