What you can build

County of San Diego ADU Regulations & Zoning


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

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.

What are the 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?

In the County of San Diego on single-family residential lots, you may build one ADU (either attached or detached) and one Junior ADU (JADUs have an owner occupancy requirement and must be converted from existing space within the primary residence).

How many ADUs does San Diego County allow for multifamily properties?

San Diego County allows up to 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)

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.

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 24′ and two stories. Read more about two story ADUs and height limits.

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?

The exterior roofing, trim, walls, windows and the color palette of the ADU shall incorporate the same features as the primary dwelling unit.


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.

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.


How many ADUs does County of San Diego allow for multifamily properties?

Up to two detached ADUs may be permitted per lot that has an existing multifamily complex. This is subject to the detached ADUs being limited to a height of 16′ and 4’ rear yard and side setbacks.

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.


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.

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.

Watch our ADU 101 Webinar

Thinking about building an ADU in San Diego and want to learn more about the whole process? We’d love to help make sure you know exactly how it all works in our on-demand webinar led by SnapADU co-founder, Whitney Hill. Hear the top tips from an expert ADU builder.