Accessory dwelling units (ADUs), also known as granny flats or in-law suites, have become an increasingly popular option for adding living space to properties with existing homes in San Diego County. In recent years, California state law and San Diego city ordinances have been updating ADU laws in San Diego to remove barriers and encourage more ADU construction to help address housing shortages.
This comprehensive guide breaks down the latest 2023 ADU laws in San Diego for regulations and processes for building detached and attached ADUs, junior ADUs (JADUs), and moveable tiny houses on lots with existing homes in San Diego.
Key Takeaways
- San Diego ADU Zones and Regulations
- Development Standards for San Diego ADUs
- Highlights of 2023 ADU Laws in San Diego
- Setback allowances, no owner-occupancy rules, and parking exemptions
- Affordable housing bonuses further incentivize ADUs/JADUs
- Moveable tiny homes permitted as ADUs given compliance with regulations
San Diego has adopted state legislation aimed at promoting affordable housing and responding to changing housing needs through ADUs and JADUs. The latest city ordinances took effect on May 6, 2023.
San Diego ADU Zones and Use Regulations
ADUs are permitted as limited uses allowed by right in the following San Diego County zones that allow residential development:
Residential Zones Allowing Detached and Attached ADUs
- All Single Dwelling Unit Zones
- All Multiple Dwelling Unit Zones
- Residential-Commercial Zones
This covers the vast majority of residentially zoned areas, encompassing single-family neighborhoods as well as multi-family areas that allow duplexes, apartments, and condominiums.
The number of ADUs permitted on a lot depends on whether it is in a Single Dwelling Unit Zone or a Multiple Dwelling Unit Zone:
ADUs Allowed By Zone Type
| Zone Type | No. of ADUs Allowed |
| Single Dwelling Unit Zone (with existing or proposed single-family home) | 1 ADU<br>1 JADU |
| Multiple Dwelling Unit Zone (existing multi-family building or lot) | 2 attached/detached ADUs <br>+ ADUs in up to 25% of existing units |
| Any residential zone | Potential additional bonus ADU (see Affordable Housing Bonus section) |
Development Standards for San Diego ADUs
San Diego’s ADU development regulations have reduced restrictions on ADUs and streamlined the approval process compared to regulations for new primary dwellings and home additions. Some of the key standards include:
ADU Setbacks
| Type of ADU or JADU | Permitted Setbacks |
| One-story ≤ 16 ft height | 0-ft interior side/rear setbacks allowed |
| One-story > 16 ft height | 0-ft side/rear setbacks allowed, unless adjacent to residentially zoned lot (then 4-ft setback) |
| Multi-story | Same as above |
These flexible setbacks ease siting constraints for detached accessory structures or additions to serve as ADUs. Other development standards:
- No minimum lot size
- No density limit
- Counted toward allowable floor area ratio (FAR)
- Can be detached or attached to primary dwelling
- No fire sprinklers required if not needed for main home
ADU Size Limits
| Type | Minimum Size | Maximum Size |
| ADU | 150 sq ft | 1,200 sq ft |
| JADU | 150 sq ft | 500 sq ft |
JADUs must be created within an existing or proposed single-family home. Detached ADU buildings can reach up to 1,200 sq ft. An ADU up to 800 sq ft is allowed on any residential lot regardless of setback, FAR, or open space constraints to encourage more flexible ADU development.
Affordable Housing Bonus
As an incentive for income-restricted affordable ADUs, property owners can get a bonus ADU for each affordable unit provided on-site:
- Additional bonus ADU allowed in a Sustainable Development Area
- 1 bonus ADU allowed outside the Sustainable Development Area
Affordability criteria are based on regional income limits, with units restricted for 10-15 years. See the San Diego Municipal Code for affordable rate calculations and eligibility details.
Highlights of 2023 ADU Laws in San Diego
Some of the key aspects of ADU laws in San Diego updated for 2023 include:
- ADUs are allowed by right in nearly all residential zones
- No minimum lot size to build an ADU
- Reduced setback requirements for ADUs and JADUs
- No owner-occupancy requirement for ADUs
- No off-street parking is required for ADUs and JADUs in most areas
- Allowance for detached, attached, or conversion ADUs
- Bonus ADU incentives for income-restricted affordable units
- Moveable tiny houses permitted as ADUs in some areas
ADU Permit Process
Constructing an ADU or JADU in San Diego involves the following key steps:
- Determine feasibility – Assess lot dimensions, zoning, and existing structures
- Design ADU – Meet size limits, setback allowances & code requirements
- Apply for building permits – Apply online with plans demonstrating compliance
- Construct ADU – Build within 180 days of permit issuance (can be extended)
- Request final inspection & certificate of occupancy – Required for legal occupancy
The City processes ADU applications through a ministerial approval process. This standardized procedure cannot require public hearings or discretionary review. Local governments must act within 60 days to approve or deny compliant ADU applications. This helps speed up permitting and approval compared to other home additions or accessory buildings.
San Diego’s zoning code also has a streamlined process that waives parking regulations and zoning deviations for building code upgrades triggered by an ADU project. This removes another potential barrier.
Moveable Tiny Houses as ADUs
In 2020, San Diego adopted new regulations allowing moveable tiny houses as ADUs. These small homes built on wheeled trailers must comply with all ADU laws in San Diego including development rules and specific design criteria for:
- Exterior cladding and windows
- Minimum roof pitch/slope
- Prohibition on slide-outs increasing interior area
Moveable tiny houses follow similar permitting and development standards to manufactured homes used as ADUs. Location and utility connection requirements also apply.
As with any ADU, moveable tiny houses on wheels cannot exceed 400 sq ft when located in certain designated areas per state law.
San Diego’s ADU experts can help assess your property and development options as per ADU laws in San Diego whether you are interested in a conventional ADU or tiny home on wheels serving as a moveable ADU per the City’s codes. They stay up to date on the details as California ADU law and local ordinances frequently change. Contact us at (657) 800-7443.
Conclusion
Reaching out to an ADU specialist is recommended before designing an ADU project to make sure you understand the ins and outs of current City policies. They can also share other financing, design, and construction considerations for bringing your ADU plans to life successfully while adapting to evolving legal requirements.
