Building an ADU in unincorporated Orange County

Unincorporated areas only

OC Development Services, part of OC Public Works, handles planning and building permits only for the county's unincorporated areas. Unincorporated communities include Rossmoor and Midway City.

If your property is inside a city, follow that city's ADU rules. We have pages for Anaheim, Irvine, Huntington Beach and Costa Mesa. For the statewide rules, see our California page. [1][2]

What you can build

The county's rules are in Orange County Zoning Code Section 7-9-90, which applies in any zoning district, including planned communities and specific plan areas. OC Development Services summarizes the current rules in its ADU fact sheet (revised January 2026).

The code section was last amended in 2020, and in places its text is stricter than the fact sheet. For example, the code allows one attached or one detached ADU (plus a JADU) on a single-family lot, only two detached ADUs on a multifamily lot, and a 16 ft height for a new ADU in a side or rear setback. The fact sheet and the county's ADU page give the newer limits described below, and the fact sheet cites the state ADU law for them. This page follows the fact sheet; if your project depends on one of these differences, confirm with OC Development Services.

Single-family properties. You can have up to three ADUs and JADUs, for a total of four homes on one lot:

• one detached ADU,
• one ADU converted from existing space, and
• one junior ADU (JADU).

Space in the house can be converted into an ADU or JADU, and so can a permitted detached building such as a garage, workshop or storage building.

Multifamily properties. On a property with an existing apartment building, you can convert non-livable space (storage rooms, basements, garages and similar) into ADUs, up to 25% of the existing units rounded down, with at least one. You can also add up to eight detached ADUs, but no more than the number of existing units; on a lot with a proposed multifamily building, up to two detached ADUs. Attached ADUs can't be built with new multifamily projects, and JADUs aren't allowed on multifamily properties.

Sewer. You must show proof of adequate sewer service. If you need a septic system, it must meet the Orange County Plumbing Code and health rules. [3][4][5]

Size, height and setbacks

Size (single-family).

• Detached ADU: up to 1,200 sq ft of interior livable space.
• Attached ADU: up to 50% of the area of the house, to a maximum of 1,200 sq ft.
• Converted ADU: no larger than the converted structure, with up to 150 sq ft added for an entrance.
• Any ADU in a setback area: up to 800 sq ft.

A 1,200 sq ft ADU is left out of lot coverage calculations. State law says an attached-ADU percentage limit can't hold an ADU below 850 sq ft, or 1,000 sq ft with more than one bedroom, and that conversions of existing space aren't subject to size limits. If those rules matter for your project, confirm with OC Development Services.

Size (multifamily). Converted and detached ADUs can each be up to 1,200 sq ft, and existing buildings can't be enlarged to create an ADU.

Setbacks. Side and rear: at least 4 ft. In the front setback, an ADU is allowed only as needed to fit an 800 sq ft ADU that can't go in the side or rear yard, and it must stay at least 4 ft from the front property line. A conversion of an existing permitted structure, or a new structure in the same footprint and height, has no added setback or height rules.

Height. On the main buildable area of the lot, an ADU follows the base zone's height limit. In setback areas the county uses the state law limits of 16, 18 or 25 ft. On multifamily properties, detached ADUs are limited to 16 or 18 ft. [3][5][6]

Parking

One parking space is required for each ADU unless one of these applies:

• the property is within a half mile walking distance of public transit, including bus stops,
• it is in an architecturally or historically significant area,
• the ADU is part of the house or an existing accessory structure,
• off-street parking permits are required but not offered to the ADU's occupant,
• a car share vehicle is located within one block, or
• the ADU has no bedrooms (a studio).

JADUs need no parking. You don't have to replace parking if the ADU is converted from, or requires removing, a garage, carport or covered parking. Required parking can be tandem on an existing driveway and can go in setback areas unless topography or fire and life safety make that infeasible. [3][5]

Fees and timeline

Impact and school fees. State law bars impact fees on an ADU with 750 sq ft of interior livable space or less, or a JADU of 500 sq ft or less; on larger units, impact fees must be charged in proportion to the unit's size compared with the main house. ADUs and JADUs under 500 sq ft of interior livable space are not subject to school impact fees.

Utility connections. The county code says an ADU or JADU attached to or inside an existing house or accessory structure doesn't need a new or separate utility connection or a related connection fee, and that an ADU isn't a new residential use when calculating connection fees or capacity charges for water and sewer.

Permit fees depend on your project; ask OC Development Services. For typical costs see our ADU cost guide.

Timeline. ADU and JADU applications are processed ministerially and need only a building permit, with no separate entitlement application. Under state law, the county must tell you within 15 business days whether your application is complete, and approve or deny a complete application within 60 days. See our ADU permit process guide. [4][5][6]

Junior ADUs and garage conversions

Junior ADUs. A JADU can be up to 500 sq ft of interior livable space, located within or attached to an existing or proposed single-family home or ADU. It needs an efficiency kitchen (sink, cooking appliances, counter and storage cabinets) and direct exterior access, and it can have its own bathroom or share one. The county code requires the property owner to live on the property when there is a JADU. State law now requires owner occupancy only when the JADU shares sanitation facilities with the house, so confirm with OC Development Services if your JADU has its own bathroom. See our junior ADU guide.

Garage conversions. A permitted garage or other detached building can become an ADU, or an ADU plus a JADU. It can grow by at most 150 sq ft, only for an entrance, and you don't have to replace the parking. See our garage conversion guide. [3][4][5][6]

Legalizing an unpermitted ADU

Under state law AB 2533, the county's Safe ADU/JADU Legalization Program helps you legalize an ADU or JADU that was built without permits before January 1, 2020. The unit is checked against the state's substandard housing standards (Health and Safety Code Section 17920.3).

Before applying, you can optionally have a licensed contractor do a confidential inspection with the county's checklist; you don't have to submit the results. Then apply for a residential building permit for an "Accessory Dwelling Unit (Custom)" project, write "AB 2533 legalization of ADU" (or JADU) in the description, include proof the unit was built before 2020 and plans of the property, and pay the permit deposit fee. Details are on the county's AB 2533 page. [7]

Renting it out

You don't have to live on the property to rent out an ADU. ADUs and JADUs can't be used as short-term rentals and must be rented for at least 30 days. The county code says an ADU or JADU is not intended for sale separately from the main house. [3][5][6]

Pre-approved ADU plans

The county's Pre-Approved ADU Plans Program offers six detached ADU plan sets to cut design costs and speed up approval: a 393 sq ft studio, a 558 sq ft one bedroom, a 748 sq ft two bedroom with one bath, an 800 sq ft two bedroom with two baths, and three bedroom, two bath plans of 972 and 1,200 sq ft. The plans currently reflect the 2022 California Building Code, and the county says it is updating them to the 2025 code.

Some site-specific work is still required. A complete package includes the plan set with its title sheet completed, a site plan, a solar plan from a solar installer, a plan preparation checklist, a hold harmless statement, a water quality form and a construction and demolition waste diversion plan. See the Pre-Approved ADU Plans page. [8]

Permit steps in Orange County

1. Confirm you are in unincorporated Orange County

   OC Development Services covers only unincorporated areas. If your property is in a city, apply to that city. [1]

2. Check the rules for your lot

   Read the county's ADU fact sheet and confirm you can show adequate sewer service. Questions go to planning@pw.oc.gov. [3][4]

3. Prepare plans

   Use a pre-approved plan with the required site plan, solar plan and forms, or have custom plans drawn. [8]

4. Apply online

   Sign in to myOCeServices, click "Apply for...", then "Permit Applications", "Private Property Permits" and "Residential Building Permits". Choose "Accessory Dwelling Unit (Standard)" for a pre-approved plan or "Accessory Dwelling Unit (Custom)" otherwise, then "Start Application". [4]

5. Plan review and permit

   The application is reviewed ministerially as a building permit, with no separate planning entitlement. The county must decide within 60 days of a complete application. [4][6]

Pre-approved and sample plans

• Pre-Approved ADU Plans Program

  Six detached ADU plan sets from a 393 sq ft studio to a 1,200 sq ft three bedroom for unincorporated Orange County; site-specific work is still required. [8]

Who to call

• OC Development Services (OC Public Works)

  ADU planning questions (planning@pw.oc.gov), building permits and inspections for unincorporated areas; permit counter at the County Service Center, Monday-Friday 8 a.m.-4 p.m.

  (714) 667-8888

  601 North Ross Street, Santa Ana, CA 92701

  [1][4][9]

Questions people ask