Building an ADU in unincorporated San Diego County

Unincorporated areas only

This page is about the parts of San Diego County that are not inside any city. The County's ADU rules apply only there: to qualify, your property must be in the unincorporated area, be residential, and have an existing or planned house. The County publishes a map of unincorporated areas.

If your address is in a city, the city's rules and permit office apply instead. See our pages for San Diego, Chula Vista, Oceanside, Escondido, Carlsbad and Encinitas. For other cities, check with that city's planning department. Statewide rules are on our California page. [1]

What you can build

The County's ADU handout, PDS-611 (revised September 2, 2026), says a residentially zoned lot with an existing or proposed house can have one newly built detached ADU, an ADU converted from existing permitted space in the house or an accessory building, and one junior ADU (JADU). The ADU can be attached to the house or detached on the same legal lot. The rules themselves are in Section 6156x of the County Zoning Ordinance.

Conversions. An existing, permitted accessory structure can be converted with no size limit; the handout's example is a 3,000 sq ft barn. Part of the house can also become an ADU, as long as part stays the main home. An ADU converted from an accessory building may add up to 150 sq ft only for getting in and out; any other addition counts as a new ADU.

Apartment and duplex lots. You can convert non-living space (storage rooms, attics, basements, garages) into ADUs, at least one and up to 25% of the existing units. You can also add detached ADUs: up to 2 with a proposed complex, or as many as the existing units, up to 8. A fourplex, for example, can add 4.

Other cases. Lots with two or more older nonconforming houses can still have an ADU and a JADU.

What HCD says. In a July 7, 2026 letter, HCD found that limiting a single-family lot to those three unit types "impermissibly restricts" the ADUs state law allows. HCD said the County must allow at least one ADU under the general state standards (for example an attached ADU, or a detached ADU larger than 800 sq ft) to be combined, in any order, with the units state law guarantees. The County had until August 6, 2026 to respond. If your plans go beyond the handout, confirm with the PDS Zoning Counter. [2][4][5]

Size, height and setbacks

Size. A detached ADU can be up to 1,200 sq ft, whatever the size of the house. An attached ADU can be up to 50% of the house's floor area, with a 1,200 sq ft cap, but an attached ADU of 850 sq ft (or 1,000 sq ft with more than one bedroom) is allowed even if that is more than 50%. The County measures floor area from the inside of the outside walls. HCD's 2026 letter says the County's code should state its limits in "square feet of interior livable space," as state law does.

Height. A detached ADU can be up to 25 feet tall. Detached ADUs at an apartment complex are limited to 18 feet, and the handout also limits ADUs under 800 sq ft to 18 feet.

Setbacks. A newly built ADU needs at least 4 feet from the side and rear lot lines, plus any setback your fire district requires. On a corner lot, the street side needs at least 4 feet. An ADU of 800 sq ft or less may go into the front setback, and needs no parking space. Converting existing permitted space needs no new setbacks, except for fire safety; additions must meet the setbacks.

Decks, patios, balconies and accessory structures attached to an ADU have their own zoning limits (Zoning Ordinance Sections 4835 and 6156.g). Ask your fire district early about fire setbacks, sprinklers and hydrants. [2][4]

Parking

The County's handout says an ADU must provide one parking space, which can be in a setback area or tandem in an existing driveway. No space is needed for an ADU under 800 sq ft, and none is needed for a JADU. If you convert or tear down a garage, carport or covered parking to build an ADU, you don't have to replace those spaces.

State law also bars parking requirements for ADUs within half a mile walking distance of public transit, in a historic district, built inside the house or an accessory structure, where on-street permits aren't offered to the ADU's tenant, or within one block of a car-share vehicle. An ADU applied for together with a new house is also exempt, but only if it meets one of those other conditions. The County lists these same exemptions for ADUs at apartment complexes. [2][6]

Junior ADUs

A JADU is up to 500 sq ft and must be entirely inside an existing or proposed house. It needs an efficiency kitchen (a cooking appliance, a food prep counter and storage cabinets) and can have its own bathroom or share one with the house. If it shares a bathroom, it must have an interior entrance to the main living area. A JADU may not have a separate electric meter, can be rented but not for less than 30 days, and can't be sold separately. More in our junior ADU guide.

Where the County and HCD disagree. The County's handout says the owner must live in the house or the JADU, that a JADU can't be attached to an ADU, and that converting a garage into a JADU means replacing the two required parking spaces. HCD's July 2026 letter says state law requires owner occupancy only when the JADU shares a bathroom with the house, that the County must remove the rule barring JADUs attached to an ADU, and that the County can't require replacement parking for a JADU. The County's Director has also said that when the Zoning Ordinance conflicts with state law, state law takes precedence. If any of these rules affects your project, confirm with the PDS Zoning Counter. [2][4][7]

Fees

The County's trial impact fee waiver for ADUs ran from January 9, 2019 to January 9, 2024 and has ended. Projects whose permits weren't issued by then pay all fees normally collected at permit issuance. Fees vary by size and construction method. You can estimate them with the County's Building Forms, Handouts and Fee Estimator page; PDS also offers estimators for transportation impact, drainage and parks fees through Online Services Central.

State law limits these fees. No impact fees may be charged on an ADU with 750 sq ft or less of interior livable space or a JADU of 500 sq ft or less; larger ADUs pay in proportion to the size of the main house. School districts can't charge impact fees on ADUs under 500 sq ft. Utilities can't treat an ADU or JADU as a new residential use for connection fees or capacity charges unless it is built at the same time as a new house. See our ADU cost guide. [1][5][6][8]

Septic, fire and site issues

Septic. Parts of the county have no public sewer. If your house is on septic, an ADU may need an extra septic tank or a new system. Approval from the Department of Environmental Health and Quality (DEHQ) on an On-site Wastewater Treatment System layout application determines whether the ADU is feasible, so contact DEHQ early.

Fire. Find out which fire protection district serves your property and ask about its requirements. Fire sprinklers are required in an ADU only if they are required for the main house. Properties in the Wildland Urban Interface have extra building and fire requirements, and fuel modification and defensible space rules apply.

Grading and solar. Steep lots may need grading permits; call the Land Development Counter at (858) 694-2055 to ask. Under the state energy code, newly built, non-manufactured detached ADUs may need solar panels; attached ADUs, conversions, prefab ADUs and JADUs are exempt. [2][5]

Renting it out or selling it

You don't have to live on the property to have an ADU. ADUs and JADUs can't be rented for less than 30 days, so vacation rentals aren't allowed.

Selling an ADU. On March 4, 2026, the Board of Supervisors adopted a program that lets owners in unincorporated communities sell an ADU separately by creating condominiums. The County's ADU Condo Guidance and Checklist explains eligibility. It supplements an application for a Tentative Parcel Map or Tentative Map and doesn't replace that process. The County's PDS-611 handout (revised September 2026) still says an ADU is not intended for sale separate from the house, so ask PDS for the current checklist and confirm your project qualifies. JADUs can't be sold separately.

Unpermitted ADUs. Under AB 2533, an unpermitted ADU or JADU built before 2020 may be able to get a permit if it meets basic health, safety and building standards. You can get a confidential third-party inspection from a licensed contractor before you apply. [1][2][5]

Permit steps in San Diego County

1. Confirm you're in the unincorporated area and check your zoning

   Check the County's unincorporated area map and get your property's zoning from a Property Summary Report (you need your APN), linked from the County ADU page. Read PDS-611. [1][2]

2. Check septic, fire and site constraints

   If you're on septic, contact DEHQ early. Ask your fire protection district about fire setbacks, sprinklers and hydrants. Ask the Land Development Counter whether you need a grading permit. [2][5]

3. Choose a design

   Hire a designer or architect, draw your own plans, buy plans or a prefab unit, or use one of the County's free standard ADU plans, completed using the Standard ADU Checklist (PDS-607). [3][5][9]

4. Submit for plan review and pay fees

   Finish your construction drawings and required calculations, then go through the pre-intake process at the County Permit Center, 5510 Overland Ave., and set up an appointment for record creation, which starts plan review. [5][10]

5. Revise and get your permit

   Revise and resubmit plans until they are approved, then pay fees and get your building permit. The permit expires after 2 years but can be extended. [5]

6. Build, pass inspections and get a certificate of occupancy

   Your contractor calls for inspections as work goes on. A Certificate of Occupancy is issued once all inspections are approved. [5]

Pre-approved and sample plans

• County of San Diego Dwelling Unit Building Plans

  Six free downloadable plan sets that can be used as detached ADUs in unincorporated areas, from 600 to 1,200 sq ft; they are about 85% complete and you add project-specific information. [1][3][5]

Who to call

• San Diego County PDS Zoning Counter

  Zoning and ADU rule questions for unincorporated areas; email PDSZoningPermitCounter@sdcounty.ca.gov or PDS.ADUQuestions@sdcounty.ca.gov

  (858) 694-8985

  County Permit Center, 5510 Overland Ave., San Diego, CA 92123 (Monday-Friday, 8:00 a.m.-11:45 a.m. and 12:30-4:00 p.m.)

  [1][10]

• San Diego County PDS Building Services

  Building permits, plan check and inspections

  (858) 565-5920

  [10]

• Department of Environmental Health and Quality

  Septic (on-site wastewater) review for ADUs; email lwqduty.deh@sdcounty.ca.gov

  (858) 694-2888

  [5]

Questions people ask