There are some similarities between the rules for ADUs in San Diego and the rules for the rest of the County of San Diego, but there are also some big differences when it comes to lot size, zoning, setbacks, permits, and bonus programs. Homeowners, investors, or builders who want to build accessory dwelling units that are legal, profitable, and safe in the area need to know these differences.
An Overview of San Diego ADU Rules
- Setbacks: There is no setback on the sides or back (4 feet is better, or for two-story/high-fire zones).
- Minimum distance between buildings: 6 feet, with some exceptions.
- Permission: You can submit a digital plan, and it usually takes 3 to 5 months.
- Parking: Most ADUs don't need any new off-street parking outside of the coastal zone.
- Guest rooms: Allowed along with ADUs, but they can't be rented or sold separately.
- ADU Bonus Program: Lets you build more units if some of them are affordable and deed-restricted. Updates for 2025 set stricter limits for each lot, especially in areas with single-family homes and high fire and hazard risk.
- Sale as a condo: The city said that ADUs could be sold as condos under AB1033.
- Fire safety rules: stricter in high-risk areas, with certain ADUs required to have minimum setbacks and sprinklers installed.
A Look at the Rules for ADUs in San Diego County
- The biggest ADU can be 1,200 square feet for a detached unit. For an attached unit, it can be 50% of the main home or 1,200 square feet, whichever is smaller (at least 800 square feet).
- Minimum setbacks of 4 feet on the sides and back, even for two-story units.
- Minimum distance between buildings: 6 feet.
- Getting a permit: You have to turn in plans in person, which takes more time and money.
- Parking: Most of the time, it's not needed, especially near transit or for conversions.
- Bonus/affordable ADUs: The county doesn't have as many bonuses as the city does.
- Fire safety rules: These rules are very different from one community to the next, and they are stricter in areas that are more likely to catch fire (like Rancho Santa Fe).
- Multifamily lots: As of January 2025, state law allows up to eight detached ADUs, or as many as there are already units, overriding stricter local rules.
Comparison Side by Side
| Requirement | City of San Diego | County of San Diego |
| Max ADU Size | 1,200 sf detached/attached | 1,200 sf detached; attached: 1,200 sf/50% |
| Setbacks | 0 ft (4 ft preferred or fire zones) | 4 ft side/rear |
| Building Separation | 6 ft | 6 ft |
| Guest Quarters | Allowed (not for rent or sale) | Not allowed if there's an ADU/JADU |
| Permitting | Digital submission takes 3–5 months | in-person submission takes a moderate amount of time. |
| Parking | Not needed unless in the coastal or impact zone | Not needed if near transit or conversion |
| Bonus Program | Big bonuses for affordable units | No full bonus program |
| Condo Conversion | Allowed under AB1033 | Not standard (as of 2025) |
| Fire Safety | Better in areas with a higher risk of fire, sprinklers | Different for each community and project, stricter |
| Multifamily Lots | Up to 8 units (2025), some conversion uncapped | Up to 8 units under SB1211 |
Differences that Matter
Zoning and Jurisdiction
The city's rules about ADUs only apply within its city limits. County codes apply to land that isn't part of a city (and some areas that have been added to other cities). It's important to check the jurisdiction because some addresses, especially those near borders or in newly annexed neighborhoods, may not follow the city's rules.
Sizes of Lots and Units
SB1211 (2025) allows up to eight detached ADUs on multifamily parcels in both the city and the county. However, single-family properties see the most differences in local code because of differences in bonus programs, deed restrictions, and provisions for affordable units.
Setbacks and Height
Both the city and the county allow for side and rear setbacks of 0 to 4 feet, but the city is a little more flexible, especially for projects that are only one story tall and not in a fire zone. Height standards are very similar, usually between 16 and 24 feet, and ADUs can only have two stories.
Guest Rooms
The city lets you have guest quarters in addition to ADUs, but the county doesn't let you have guest quarters if you have an ADU or JADU. In both places, guest quarters have their own size and facility limits.
Getting Permission and Setting a Date
Digital submissions and a quicker review schedule (3 to 5 months) make things easier for the city. The county needs applications to be made in person, and the approval times are usually moderate. However, rural and low-density projects often have less of a backlog.
Requirements for Parking
Both areas usually don't require parking for ADUs if they are close to public transportation or in certain situations (like conversions). This is in line with state law, which overrides most local rules that are stricter for lots near public transportation.
Bonus/Affordable ADU Program
Changing a condo
Fire and Safety
Requirements are different, especially in areas that are marked as having a high or very high fire risk. Both need special setbacks, defensible space, and sometimes fire sprinklers. This affects places like Rancho Santa Fe and city neighborhoods next to wildland areas.
Frequently Asked Questions
Who decides whether city or county rules apply?
To make sure you know the ADU rules for a certain property, you can call the city planning office or the county development office, or you can use the interactive jurisdiction lookup tools.
How many ADUs can fit on one lot?
For a single-family home, there is one ADU and one JADU in both the city and the county. For multifamily, there can be as many as 8 or as many as there are legal units.
What about the height of buildings and setbacks?
- City: 0 feet for single-story ADUs, more for two-story ADUs or areas with a higher risk of fire (4 feet minimum).
- County: All buildings must be at least 4 feet tall, and the maximum height depends on the zone.
Does the city or county make it easier to build ADUs?
The city of San Diego's program (especially the pre-2025 rollbacks) gives you more options for building multiple units on a single parcel through the bonus/affordable program. The county, on the other hand, only follows state minimums.
