Who this applies to
County Planning & Development Services (PDS) covers ADUs on residential property in the unincorporated areas, where the lot has or will have a main house. Your property must be zoned residential. You can check zoning with a Property Summary Report using your Assessor's Parcel Number (APN).
The county says that where its zoning rules conflict with state law, state law wins.
Source: https://www.sandiegocounty.gov/content/sdc/pds/bldg/adu.html. Checked 2026-10-22.
Size
| Type | Limit |
|---|---|
| Detached ADU | Up to 1,200 sq ft; size does not depend on the main house |
| Attached ADU | Up to 50% of the main house, capped at 1,200 sq ft; exceptions to the 50% limit may apply if the main house has more than one bedroom |
| JADU | Up to 500 sq ft, entirely inside an existing or planned house |
The county's April 2024 handbook adds that a conversion of an existing permitted building is not held to size, height or lot coverage standards. It also says conversions keep their existing setbacks.
Source: https://www.sandiegocounty.gov/content/sdc/pds/bldg/adu.html; https://www.sandiegocounty.gov/content/dam/sdc/pds/bldg/adu_info/COSD_ADU_Handbook.pdf (April 2024 handbook). Checked 2026-10-22.
Setbacks, height and parking: what the handbook says
These figures come from the county's April 2024 ADU Handbook. The county amended its ADU ordinance on March 4, 2026, and state law now bars parking requirements in more cases than the handbook lists (see the state guide). Confirm each figure with PDS before relying on it.
| Item | What it says |
|---|---|
| Detached ADU height | 25 ft (18 ft on multifamily complexes) |
| Attached ADU height | No more than the main building or 16 ft, whichever is higher; if built above part of an existing home, the zone height limit |
| Side and rear setbacks | 4 ft minimum for new detached and attached ADUs |
| Front setback | The zone setback; for a detached ADU, unless lot constraints make that impossible |
| Conversions | Existing setbacks stay; no parking required; no size, height or lot coverage standards for a permitted structure |
| Parking (new ADU) | One space, which can be in setbacks or a driveway; none if within half a mile of public transit or in a historic district |
| JADU parking | Not required |
Source: https://www.sandiegocounty.gov/content/dam/sdc/pds/bldg/adu_info/COSD_ADU_Handbook.pdf. Checked 2026-10-22.
How many units
A single-family lot can have one ADU (attached, detached or converted) and one JADU, per the 2024 handbook. The handbook also says multifamily lots get at most two detached ADUs. State law has since raised that to up to eight on a lot with an existing multifamily building (see the state guide), and the county's project page says its 2026 ordinance amendment incorporates that change.
Source: https://www.sandiegocounty.gov/content/dam/sdc/pds/bldg/adu_info/COSD_ADU_Handbook.pdf; https://www.sandiegocounty.gov/content/sdc/pds/longrangeplanning/ADU-ZO.html. Checked 2026-10-22.
Renting and owner occupancy
The county does not require the owner to live on the property for an ADU. It does for a JADU. ADUs and JADUs must be rented for more than 30 days, so no vacation rentals.
Source: https://www.sandiegocounty.gov/content/sdc/pds/longrangeplanning/ADU-ZO.html; https://www.sandiegocounty.gov/content/dam/sdc/pds/bldg/adu_info/COSD_ADU_Handbook.pdf (FAQ, April 2024). Checked 2026-10-22.
Permit steps
- Confirm your property is in the unincorporated county, residential, and has or will have a main house.
- Read the county ADU Handbook and the plan submittal checklist.
- Check septic and fire district requirements early. Properties on septic need Department of Environmental Health and Quality sign-off, and your fire district sets fire rules.
- Submit plans for a building permit. The handbook says to expect several weeks and possibly several rounds of comments.
- Pay fees, build, pass inspections, then occupy.
Source: https://www.sandiegocounty.gov/content/sdc/pds/bldg/adu.html; https://www.sandiegocounty.gov/content/dam/sdc/pds/bldg/adu_info/COSD_ADU_Handbook.pdf. Checked 2026-10-22.
Fees and the ended waiver
The county's ADU plan check fee waiver trial started January 9, 2019 and ended January 9, 2024. If your permit was not issued by that date, you pay the fees normally collected at permit issuance. The county points to its Building Forms, Handouts and Fee Estimator for amounts; none are quoted here.
Source: https://www.sandiegocounty.gov/content/sdc/pds/bldg/adu.html. Checked 2026-10-22.
County pre-approved plans
The county offers dwelling unit plans you can use as a detached ADU, about 85% complete. You fill in project-specific details. Plans A through F are ADU-eligible and range from 600 to 1,200 sq ft; plans G and H are for single-family homes only.
| Plan | Size | Rooms |
|---|---|---|
| A | 1,200 sq ft | 3 bedroom, 1 bath |
| B | 1,200 sq ft | 2 bedroom, 1 bath |
| C | 1,200 sq ft | 2 bedroom, 2 bath |
| D | 1,000 sq ft | 1 bedroom, 1.5 bath |
| E | 800 sq ft | 1 bedroom, 1 bath |
| F | 600 sq ft | 1 bedroom, 1 bath |
The county says it has offered pre-approved ADU plans since 2019.
Source: https://www.sandiegocounty.gov/content/sdc/pds/bldg/adu_plans.html; https://www.sandiegocounty.gov/content/sdc/pds/longrangeplanning/ADU-ZO.html. Checked 2026-10-22.
Selling an ADU separately (2026)
On March 4, 2026 the Board of Supervisors adopted a program under state law AB 1033 that allows an ADU to be sold separately through a condominium conversion. It took effect April 4, 2026.
Effective September 18, 2026 the county added three rules for ADU condominiums: a right of first refusal contract that each condominium owner on the lot must set up with an existing tenant or another owner on the lot, an affidavit from new buyers that they or a family member will live in the unit as a primary residence for a defined period, and a required public listing period, with a disclosure that the unit is offered to buyers who will live in it, each time a unit is listed. The county's pages do not give the length of the periods in the text read here.
Source: https://www.sandiegocounty.gov/content/sdc/pds/longrangeplanning/ADU-ZO.html. Checked 2026-10-22.
Older unpermitted ADUs
If you have an unpermitted ADU or JADU built before January 1, 2020, state law AB 2533 may let you get it permitted if it meets health, safety and building standards. The county offers a substandard structure checklist and allows a confidential third-party code inspection before you apply.
Source: https://www.sandiegocounty.gov/content/sdc/pds/bldg/adu.html. Checked 2026-10-22.
What this guide leaves out
- Current setbacks, height and parking under the March 2026 ordinance. This guide uses the April 2024 handbook for those, so check them with PDS.
- County fee amounts and plan check times.
- Fire district rules, which vary by district.
Confirm with County PDS before you rely on any figure.
Weighing an ADU as a rental? Run the rental cash flow calculator with your own numbers. Inside the city, see the city ADU guide. For the state baseline, see California ADU rules.
FAQ
Which ADU rules apply if I live in the unincorporated county?
County Planning and Development Services rules apply, not a city's. Check that your address is in the unincorporated area first.
Is there still a county ADU fee waiver?
No. The county trial waiver of the plan check fee ended on January 9, 2024.
Does the county have pre-approved ADU plans?
Yes. Plans A through F, from 600 to 1,200 square feet, are about 85 percent complete and can be used as a detached ADU.
Can I rent my county ADU on Airbnb?
No. The county says ADUs and JADUs must be rented for more than 30 days.