What you can build
County of San Diego ADU Regulations & Zoning
Navigating ADU regulations can be challenging, but with over 100 projects under our belt, we have an in-depth understanding of the nuances involved. We share our knowledge to ensure that individuals receive reliable information rather than simple restatements of facts. Our insights were last refreshed in March 2026.
Key Facts SnapShot
Size and Separation
Maximum size 1200 sqft
Side/rear setbacks 4 feet
Two story Yes
Building separation 6 feet
Additional Requirements
Soils Report No
Building Verification Survey No
Coastal permit (in some areas) No
Stormwater Mitigation No
Permitting timeline
Standard Timeline: 3-5 months
Coastal Timeline: TBD
Permit Costs: $15-18/sqft
Our ADU experience in San Diego County
Unincorporated areas are covered by the County of San Diego’s ADU rules and regulations. Additionally, some city properties are subject to County of San Diego ADU rules and regulations. This will depend on whether your city has incorporated the land on which your property is located. In some cities like Vista, San Marcos, Escondido, Oceanside, Encinitas, Del Mar, Chula Vista, El Cajon, Santee, and parts of San Diego, portions are regulated by County of San Diego and not the city. If you don’t know what jurisdiction applies to your property, we can look that up for you in early phases of our discussions.
The County requires in-person submission of plans, which adds some processing time and expense. Review times are moderate. Other agencies that are more proximate to the location of the residence may require input and approval (i.e., local fire agencies). The County has also put out standard floor plans, which some homeowners have found helpful as a starting place for their ADU designs.
When do County of San Diego ADU regulations apply?
Whether County of San Diego ADU regulations will apply to your project depends on the city incorporations that pertain to your property. If you’re a property owner in unincorporated areas such as Bonita, Bonsall, Del Dios, Fairbanks Ranch, Fallbrook, Hidden Meadows, Lakeside, Mount Helix, Pala, Pala Mesa, Pauma Valley, Rancho Santa Fe, Rainbow, Spring Valley, Sweetwater, Twin Oaks, Valle De Oro, Valley Center, or 4S Ranch, your project falls under the County of San Diego’s ADU rules and regulations.
Additionally, some properties within other city boundaries may also fall under County regulations, depending on whether the land on which your property is located is incorporated or not. For instance, cities like Vista, San Marcos, Escondido, Oceanside, Encinitas, Del Mar, Chula Vista, El Cajon, Santee, and even parts of San Diego, have portions governed by County regulations, not city laws.
If you’re unsure about the regulations that apply to your property, our team at SnapADU can help. During our early conversations, we can look up your property specifics and guide you on the right path to building your ADU in the County of San Diego. You can also use this lookup tool from the County to determine your jurisdiction.
Recent Changes to San Diego County ADU Regulations (2025–2026)
The County recently updated its ADU ordinance, primarily to reorganize and clarify its rules and realign local code with state law. Most state-level ADU changes from recent legislation (e.g., owner-occupancy removal, expanded multifamily ADU allowances, ADU amnesty, and preapproved plan requirements) were already regardless of the local ordinance language.
On March 4, 2026 the County Board of Supervisors voted to adopt AB1033 which allows ADUs in the county jurisdiction to be subdivided and sold separately, similar to condominium units. Implementation will go into effect on April 4, 2026. Additional parameters are to be considered to promote first-time home buyers such as owner occupancy requirements and first right of refusal for existing tenants which will be determined within 120 days (July 2, 2026).
What are the current rules for an ADU in San Diego County?
We’re glad you asked! Check out our summary below, where you can find how many ADUs you can build, plus limitations for size, setbacks and other additional requirements. We’ve included our own experience with how the laws are interpreted based on designing, permitting & building many ADUs in the County.
Number of ADUs Allowed
How many ADUs can you build in San Diego County?
On single-family lots in the County of San Diego, state law now supports a broader mix of ADU types than many homeowners previously realized. Under California law, a single-family property may combine:
- one standard ADU under the regular local-rules pathway
- one detached ADU up to 800 square feet
- one ADU created from existing space in the primary home or an accessory structure
- one JADU created from existing space in the primary residence, up to 500 square feet
HCD’s updated 2026 ADU Handbook explains that local agencies must allow the single-family combinations described in Government Code section 66323 and, in addition, must allow at least one unit described in section 66314.
However, note that local adoption will take some time. We are currently awaiting HCD’s feedback on the County of San Diego’s interpretation.
Read more in our guide to how many ADUs you can build on a single-family property.
How many ADUs does San Diego County allow for multifamily properties?
San Diego County allows at least 2 detached ADUs for multifamily lots with an existing multi-family building. (Meaning: In order to build 2 ADUs, the property must already have at least a duplex on it, not just a single family dwelling)
Multifamily property owners are permitted to build as many ADUs as there are existing units, with a maximum of eight detached ADUs.
Additionally, a minimum of one accessory dwelling unit, or up to 25 percent of the existing multifamily units, is permitted within an existing multifamily dwelling, as a result of the conversion of non-habitable space including, but not limited to, storage rooms, boiler rooms, passageways, attics, basements, or garages.
Read more about the rules around how many ADUs you can build on a multifamily lot.
Can you build guest living quarters in San Diego County?
As of March 2026, guest quarters are allowed on properties with ADUs. Note this information was confirmed via email by a County Planning Manager; the County plans to update the Guest Quarters handout with this information.
Guest quarters cannot include kitchens, wet bars, or laundry facilities. These units must not function as separate dwellings or be rented out. Stays are restricted to a maximum of 30 days per calendar year.
Size restrictions dictate that guest quarters cannot exceed 30% of the main home’s square footage, with a maximum of 600 square feet. Additional space up to 50% of the main home’s size may be granted through an Administrative Permit. Only one electric meter is allowed for both the main home and guest quarters.
They are permitted in specific zoning areas (A70, A72, RR, RS, RV, RU, RRO, S88, S90, and S92). In RS, RV, RU, RRO, and S88 zones, the lot must be at least 20,000 square feet unless an Administrative Permit is obtained.
Read more about guest quarters.
ADU Size & Building Constraints
What size detached ADU can you build in County of San Diego?
County of San Diego allows for a detached ADU up to 1200 sqft. ADUs up to 800 square feet are exempt from lot coverage requirements. (Meaning: You can build an ADU of this size even if you’re maxed out on lot coverages).
What is the height requirement for an ADU in County of San Diego? Can you build a 2-story ADU in County of San Diego?
The height of a detached ADU can be up to 25′ and two stories. Read more about two story ADUs and building an ADU above a garage.
Does County of San Diego allow roof decks on ADUs?
No, roof decks are not permitted on detached ADUs in County of San Diego.
How big can an attached ADU be in County of San Diego?
The square footage of any attached ADU may not to exceed 50% of the primary dwelling square footage, or 1,200 sqft, whichever is less, but not less than 800 square feet.
What are the requirements of the exterior of the ADU?
County does not list any specific requirements for the color, style, or materials of the exterior of the ADU.
Setbacks
What is the setback requirement for an ADU in County of San Diego?
ADUs must comply with the required front & exterior side yard setbacks and a minimum side and rear setback of at least 4’ (except any required fire setbacks).
Per a Principal Planner in a meeting of December 2022, ADUs of 800 square feet or under can be built in Front Setback if you cannot locate within the backyard. No maximum encroachment, though the county will use some discretion and won’t allow zero lot lines if there is space to push back from the property line. Also, if an ADU in the rear requires an extra permit, a front yard ADU would be allowed. Read more about setbacks and front yard ADUs.
What is the minimum distance the ADU must be from existing structures?
The minimum required distance between structures is 6′, with 4′ eave to eave.
Additional Requirements
Does County of San Diego require in-person submission of plans for an ADU?
Yes, County of San Diego requires in-person submission of plans and does not accept digital applications at this time.
Does County of San Diego require a soils report for an ADU?
No, the County of San Diego typically does not require a soils report.
Does County of San Diego require coastal development permits?
Only a small unincorporated portion of Rancho Santa Fe is within the Unincorporated LCP Coastal Zone. At this time it is undetermined what requirements for an ADU would be in those areas, though we are quite familiar with ADUs in coastal zones elsewhere in Greater San Diego and would navigate as required.
Does County of San Diego have additional regulations for Fire?
Fire safety regulations can vary widely by community in the County of San Diego. In some communities, such as Rancho Santa Fe, stricter standards apply. These include ensuring adequate fire truck access, installing automatic sprinkler systems, and providing sufficient water supply which may include installing water tanks on the property. Creating defensible space around the ADU is also required, which can involve clearing vegetation, planting fire-resistant plants, and maintaining distance from trees. Multi-story ADUs may require additional safety measures like fire alarm systems and emergency voice alarm systems. The fire code official has the authority to modify some requirements based on specific circumstances to ensure fire safety.
Can I sell my ADU separately from my main home?
Not yet, but as of fall 2025 theCounty of San Diego is soliciting feedback from the public on their draft ordinance to allow the sale of ADUs. Feedback will be accepted through the end of the year, with a board hearing in early 2026. So the earliest a sale could be possible would be some time in 2026. Read more in our guide to AB1033.
Multifamily
How many ADUs does County of San Diego allow for multifamily properties?
Multifamily property owners are permitted to build as many ADUs as there are existing units, with a maximum of eight detached ADUs. This change is due to California state law and will pre-empt existing local laws that are not brought into conformance.
Additionally, a minimum of one accessory dwelling unit, or up to 25 percent of the existing multifamily units, is permitted within an existing multifamily dwelling, as a result of the conversion of non-habitable space including, but not limited to, storage rooms, boiler rooms, passageways, attics, basements, or garages.
What if you have a multifamily dwelling on a lot that is not zoned for multifamily? You may build one ADU, as per County code, properties that have multiple (2 or more) existing, non-conforming single family dwellings (SFDs) and are in a residential zone that only allows for one SFD, can have one ADU (JADU is not allowed due to multifamily status of the unit).
Can you stack detached ADUs on top of each other?
No, you cannot stack ADUs on top of each other in County of San Diego.
Can you attach two ADUs to each other in County of San Diego?
No, you cannot attach two ADUs. The County has interpreted that multi-family lots are permitted two freestanding, detached accessory dwelling units which are detached from the multi-family residence as well as from one another.
Can you convert existing space to an ADU?
Yes, existing non-livable space may be converted to ADUs (e.g. storage areas and garages). The minimum number of ADU conversions allowed is one, up to a maximum equal to 25% of the number of existing multifamily units. This is in addition to the allowed number of detached ADUs.
Parking
What is the parking requirement for an ADU in San Diego County?
A parking space is not required for an ADU in any of the following instances:
o Within a one-half mile walking distance from public transit, which includes bus stops.
o Within an established historic district.
o Converted from the existing space of a primary residence or accessory structure, or are attached to an existing or proposed primary residence.
Effective Jan 2025 (SB1211): When a garage, carport, covered parking structure, or uncovered parking space is demolished or converted for construction of an ADU, replacement parking will not be required.
Where can a parking space be located?
If a parking space is required, it may be located within the setbacks and in an existing driveway as tandem parking. Parking spaces don’t need to be replaced when a garage, carport, or covered parking structure is demolished in conjunction with the construction of an ADU or converted to an ADU.
Additional County of San Diego ADU Regulation Resources
Accessory Dwelling Units Overview – County of San Diego Planning & Development Services
Search ADU Plans
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About SnapADU
Since 2020, we’ve focused exclusively on designing, permitting, and building over 100 ADUs in San Diego. Our deep experience means we catch what others might miss, and our in-house team ensures every promise is delivered.
Learn MoreHow much does an ADU cost in San Diego County?
Glad you asked! Head on over to our ADU costs page for detailed info on all the different costs that go into building an ADU. You’ll see why the all-in cost can range from $300K to $450K+ depending on the size ADU you are building, as well as your property’s unique additional costs.
How much will an ADU rent for in San Diego County?
Below are median rental prices by zip code and bedroom count. Be sure to run comps for your specific area or check with a realtor.
RENT RATES IN COUNTY OF SAN DIEGO
| Zip | Jurisdiction | City | 1BR | 2BR | 3BR |
| 91902 | County of San Diego | Bonita | 1835 | 2460 | 3390 |
| 92003 | County of San Diego | Bonsall | 1970 | 2575 | 3285 |
| 92028 | County of San Diego | Fallbrook | 1705 | 1930 | 2640 |
| 92091 | County of San Diego | Rancho Santa Fe | 2070 | 3115 | 5065 |
| 91977 | County of San Diego | Spring Valley | 1610 | 2230 | 2940 |
Source: Rentometer March 2026. Note: Because ADUs are still a relatively small portion of the rental market, many comparables come from apartments, condos, or single-family homes. Smaller ADUs are usually compared to apartments, while larger ADUs are often compared to single-family homes. New construction ADUs may be able to command slightly higher rents than older apartment units.