As California faces ongoing housing shortages, Accessory Dwelling Units (ADUs) have become a key solution across the state, including in San Diego County. With updated local ordinances aligning with state mandates, homeowners now have greater flexibility to build secondary units on their property. However, understanding the specific zoning rules, setbacks, size limits, and permit process is essential for compliance and success.
In this article, we’ll cover all the key regulations, permitted zones, and legal pathways to build an ADU in unincorporated San Diego County in 2025.
What is an ADU in San Diego County?
An Accessory Dwelling Unit (ADU) is a residential dwelling unit that provides complete independent living facilities for one or more people. ADUs can be:
Detached: Separate structure from the main home
Attached: Physically connected to the main house
Converted: From existing space like garages, basements, or attics
Zoning Laws for ADUs in San Diego County (2025 Update)
ADUs are permitted in all residential zones in unincorporated San Diego County. This includes the following zoning types:
R-1 (Single-family residential)
RS, RR, RU, and RE zones
Multi-family zoning districts (with additional ADU allowances)
Each zone may have varying rules for development, but recent state law has standardized many of the requirements across California.
Key ADU Zoning Regulations and Setbacks
| Regulation | Requirement (2025) |
|---|---|
| Minimum Lot Size | No minimum lot size for ADUs |
| Max ADU Size | 1,200 sq. ft. for detached units |
| Height Limits | Up to 16 ft by default (can increase near transit) |
| Front Setback | Varies by zone, but typically 20 ft |
| Rear/Side Setback | 4 ft minimum |
| Fire Access/Defensible Space | Must meet wildfire and safety codes |
| Utility Connections | Separate not always required; may share with main unit |
Allowed ADUs Per Lot
🏠 Single-Family Homes: 1 ADU + 1 Junior ADU (JADU)
🏢 Multi-Family Properties: Up to 2 detached ADUs + conversions from non-livable spaces (e.g., storage rooms)
Junior ADU (JADU) Specifics
A Junior ADU is a smaller living space (up to 500 sq. ft.) created within the existing primary residence.
Must include an efficiency kitchen
Bathroom can be shared with the main house
Owner occupancy is required (for JADU only)
Permit Process for ADUs in San Diego County
To build a legal ADU, follow these steps:
1. Pre-Application Research
Confirm zoning and property eligibility on the County Zoning Portal.
2. Develop Plans
Hire an architect or designer to create site and floor plans compliant with state/local codes.
3. Submit Application
Apply via the San Diego County Planning & Development Services (PDS).
Upload plans, calculations, and forms online.
4. Pay Applicable Fees
Fees depend on square footage, type of unit, and location. Fee waivers may apply for units under 750 sq. ft.
5. Schedule Inspections
Work must be done by licensed professionals and inspected throughout key stages of construction.
| Condition | Parking Requirement |
|---|---|
| Within ½ mile of public transit | No parking required |
| ADU is part of existing structure | No parking required |
| Converted garage | No replacement parking required |
| Detached ADU not near transit | 1 space per unit (can be tandem) |
Development Incentives & Fee Waivers (2025)
To encourage more ADUs, San Diego County offers:
Impact fee waivers for units under 750 sq. ft.
Pre-approved ADU plans
Expedited review timelines
Reduced development standards near transit zones
FAQ
Final Thoughts
ADUs are one of the most effective ways to address California’s housing crisis while increasing your property value and flexibility. The County of San Diego has updated its ADU regulations to reflect statewide mandates and support local homeowners in building legally and efficiently. Whether you're planning a backyard rental or a family suite, now is the perfect time to explore your ADU potential.
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