The Complete Orange County ADU Requirements Guide
If you’re planning to build an accessory dwelling unit (ADU) in Orange County, understanding the local rules is a critical first step. An ADU is a self-contained housing unit that shares a lot with a larger main residence. Whether it’s used for guests, as a rental, or extra living space, adding an ADU requires navigating zoning, permitting, and construction standards.
This guide covers what you need to know about building an ADU in unincorporated Orange County, plus how Samara can help.
Orange County ADU regulations at a glance
California law requires all jurisdictions to allow ADUs in residential zones, and Orange County has adopted standards in line with those rules. The County’s permitting timeline includes a 60-day initial review, with most projects taking three to four months from submission to approval.
Below are the key regulations for ADUs in unincorporated Orange County. Note: cities within the county may have their own ADU rules.
Size and lot requirements
Size limits depend on the type of ADU:
- Detached ADUs can have up to 1,200 square feet of floor area. Height is generally limited to 16 feet, but this can increase to 18 feet if the ADU is within one-half mile of public transit or on a lot that has an existing multistory multifamily building.
- Attached ADUs can be up to 50% of the main residence’s floor area, with a 1,200-square-foot cap. In most cases, they can be up to two stories tall. Local rules must allow Orange County ADUs to be up to 25 feet tall, or the height allowed for the primary dwelling, whichever is lower.
- Junior ADUs (JADUs) must be created within an existing or proposed single-family home. They must be between 150 and 500 square feet.
Orange County imposes no minimum lot size for ADU projects, but requires a minimum setback of four feet from rear and side property lines for new ADUs.
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Design requirements
Depending on your location in Orange County, your ADU may be subject to specific design standards. Unincorporated areas of the County generally do not add extra aesthetic requirements beyond the state’s basic standards, but incorporated cities can adopt their own objective design criteria. For example, within the City of Orange, ADUs are required to meet certain style guidelines, and should:
- Use at least two different exterior colors on the structure (e.g. base and trim) for visual contrast.
- Incorporate at least three architectural elements that add visual interest (such as trellises, exposed rafters, columns, or bay windows).
- Use a roof form and pitch that are consistent with the primary residence.
Additional design rules may apply for ADUs located in designated historic districts to ensure neighborhood compatibility.
Parking requirements
One parking space is required for each detached ADU in Orange County. This requirement is waived if your property is within a half mile of public transit, in an architecturally or historically significant district, or if a car-share vehicle is located within one block of the ADU.
No parking is required for ADUs that are attached to or part of the primary residence, for JADUs, or for ADUs that are studio units with no separate bedrooms.
Zoning eligibility
In unincorporated Orange County, ADUs are allowed on any lot that is zoned for residential use (single-family or multi-family) as long as a primary dwelling exists on the property or is being built. This includes mixed-use zones that permit residential development.
Incorporated cities within Orange County may have their own zoning restrictions, but all jurisdictions must adhere to California’s broad allowances for ADUs in residential areas
Number of ADUs allowed
On single-family properties, you may add one ADU and one JADU per lot at most. The County requires that either the primary home or the JADU be owner-occupied if a JADU is built; if no owner lives on site, you are limited to one ADU. In other words, a single-family lot can have up to three units (the primary house, an ADU and a JADU) if owner occupied, or two units (the primary house and one ADU) if not.
For multi-family properties, multiple ADUs are permitted. Portions of an existing multi-family building that are not used as livable space (for example, storage rooms, boiler rooms, garages, or other ancillary areas) may be converted into internal ADUs, up to a maximum of 25% of the existing unit count rounding down to the nearest whole unit. Additionally, you may construct up to two new detached ADUs on a multi-family lot, regardless of the building’s size.
Meet the KurodasStreamline your ADU in Orange County
If you’re looking to build an ADU, Samara makes it easy. We handle everything from permits to installation and even offer our own financing. Call us at 650-420-2607 to schedule a 15-minute consultation and discover how simple adding a Backyard ADU can be.
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