ADU Rules in Orange County, California
We track 12 cities in Orange County. Each city writes its own ADU ordinance on top of California law, so size limits, fees, and design rules differ from one city to the next. Among the cities we track, Santa Ana has the lowest starting permit fees ($5,500 – $12,000).
Cities
12
Max Detached Size
1,000–1,200 sq ft
Build Costs From
$120,000
Pre-approved Plans
6 of 12 cities
Orange County Cities Compared
| City | Max detached | Height | Permit fees | Build cost |
|---|---|---|---|---|
| Anaheim | 1,200 sq ft | 16 ft (detached, single-family lot) | $6,000 – $14,000 | $140,000 – $300,000 |
| Santa Ana | 1,000 sq ft | 20 ft or two stories (detached) | $5,500 – $12,000 | $120,000 – $260,000 |
| Irvine | 1,200 sq ft | 16 ft | $8,000 – $18,000 | $160,000 – $340,000 |
| Huntington Beach | 1,200 sq ft | 16 ft | $8,000 – $18,000 | $175,000 – $380,000 |
| Garden Grove | 1,200 sq ft | 16 ft detached (18 ft on a lot with a multistory multifamily building) | $8,000 – $17,000 | $160,000 – $330,000 |
| Fullerton | 1,200 sq ft | Zone height limit for attached and detached ADUs | $8,000 – $16,000 | $160,000 – $330,000 |
| Orange | 1,000 sq ft | 16 ft (detached) | $8,000 – $17,000 | $165,000 – $340,000 |
| Costa Mesa | 1,200 sq ft | Up to two stories, not taller than the main home allowed on the lot | $9,000 – $18,000 | $175,000 – $360,000 |
| Mission Viejo | 1,200 sq ft | 16 ft (detached) | $8,000 – $16,000 | $165,000 – $335,000 |
| Westminster | 1,200 sq ft | 16 ft | $8,000 – $16,000 | $165,000 – $335,000 |
| Lake Forest | 1,000 sq ft | 16 ft (detached) | $8,000 – $16,000 | $165,000 – $335,000 |
| Newport Beach | 1,200 sq ft | 16 ft | $10,000 – $20,000 | $200,000 – $410,000 |
Anaheim ADU rules
Anaheim runs an ADU Express program: a qualifying new detached ADU on a single-family lot built from a city pre-approved plan can clear review in 1 to 3 days with no design cost. Before applying you need written confirmation of sewer capacity from Public Works. Detached units need 10 ft of separation from the main house.
Santa Ana ADU rules
Santa Ana caps detached ADUs at 1,000 sq ft but allows them up to 20 ft or two stories, which helps on the city's many small lots. The city's Pre-Approved ADU Plans Program offers detached designs in Ranch, Spanish, Traditional and Contemporary styles. Garage conversions remain the most common project.
Irvine ADU rules
Irvine is a master-planned city where many villages have their own design guidelines and HOAs, so ADU design review can involve more than city zoning. HCD issued findings on Irvine's ADU ordinance in January 2025, and state standards control where the local ordinance conflicts. Detached ADUs can reach 1,200 sq ft and 16 ft, with attached units allowed up to 25 ft.
Huntington Beach ADU rules
Most of Huntington Beach lies in the Coastal Zone, so many ADUs need a Coastal Development Permit, which can add months to approval. The city offers one pre-approved plan: a 490 sq ft, one-story detached ADU in three architectural styles, used without modifications. Outside the Coastal Zone the process follows standard state timelines.
Garden Grove ADU rules
Garden Grove runs ADU Go, a set of four city-owned pre-approved ADU plans that homeowners can use for free. Most lots are compact (about 5,000 to 7,000 sq ft), so garage conversions and careful rear-yard placement are common. Short-term rentals are not allowed in the primary home, ADU or JADU.
Fullerton ADU rules
Fullerton's ADU rules are in Municipal Code Section 15.17.100, which the City Council amended in June 2025 to track recent state law. Older R-1 neighborhoods near the colleges have many deep rear yards and detached garages suited to ADUs, while hillside areas such as Sunny Hills may need grading review. Orange County Fire Authority handles fire and life-safety review.
Orange ADU rules
Orange regulates ADUs in Municipal Code Chapter 17.29, which caps new ADUs at 850 sq ft with fewer than two bedrooms and 1,000 sq ft with two or more. Applications go through the city's Civic Portal and must be acted on within 60 days of being deemed complete. Old Towne Orange lots often have alley garages suited to conversion, but historic design guidelines apply.
Costa Mesa ADU rules
Costa Mesa runs a Safe ADU Legalization Program for owners of unpermitted units and has set up a pre-engineered ADU plan program. Plans are submitted electronically through the city's TESSA portal for combined Planning, Building, Public Works and Fire review. The city allows ADUs as small as 150 sq ft.
Mission Viejo ADU rules
Mission Viejo regulates ADUs and JADUs under Municipal Code Section 9.10.020(12) and publishes an ADU Reference Guide. Most neighborhoods sit inside master-planned HOA communities, so check CC&Rs and architectural review early, although the city itself must approve a state-law ADU administratively. New attached or detached ADUs may need one parking space unless a state exemption such as nearby transit applies.
Westminster ADU rules
Westminster has a preapproved standard plan for detached ADUs, but it is not pre-permitted: you still need a full plan check and a licensed professional to prepare the site plan and existing floor plans. Detached ADUs can be up to 1,200 sq ft and 16 ft tall. Lots are modest, and multigenerational households make garage conversions popular.
Lake Forest ADU rules
Lake Forest posts its ADU permit application, applicant's guide and FAQs on the Planning Applications page, and ADU applications must be filed in person at City Hall. The city targets 10 business days for a first ADU review and 5 for resubmittals, and it runs an Affordable ADU Loan Program tied to a deed restriction. Many neighborhoods are Planned Community zones with HOA design rules.
Newport Beach ADU rules
Most of Newport Beach lies in the Coastal Zone, so ADUs there are governed by both the zoning code (Section 20.48.200) and the Local Coastal Program implementation plan (Section 21.48.200). Coastal Zone review can add months to a project, and harbor-front lots may carry extra overlay rules. Fees here run higher than in most Orange County cities.
Rules that apply in every California city are summarized in our California ADU law guide. See all California cities or compare every city side by side.