ADU rules in San Diego County

Detached ADUs are allowed with any proposed or existing primary residence, single-family or multifamily, on lots where the Zoning Ordinance permits Residential and Agricultural use types in the unincorporated county (the 18 cities, including the City of San Diego, have their own rules): Section 6156 lists ADUs among the accessory uses permitted in those zones, and 6156.x.A.1 requires only that a detached unit sit on the same legal lot as the house. Under the local standards of 6156.x.A a detached ADU may reach 1,200 sq ft and 25 feet, with 4-foot side and rear setbacks and the zone's front setback, which it may encroach into when needed to fit a unit of 800 sq ft or less (A.15 to A.17). The ministerial track of 6156.x.B (Gov. Code 66323) adds an 800 sq ft, 18-foot detached unit with 4-foot setbacks that can be combined on a single-family lot with an ADU converted from existing space and a JADU, and on multifamily lots allows up to eight detached ADUs beside an existing building (never more than its existing unit count) or two beside a proposed one. HCD's July 7, 2026 findings letter reads 6156.x.A.22 and B as limiting a single-family lot to one of each and calls that unlawful, because at least one Gov. Code 66314 unit (its example: a new 1,000 sq ft detached ADU) must be allowed in any order alongside the 66323 units, which would permit a larger detached ADU in addition to the 800 sq ft exempt one; Ord. No. 11016 re-enacted the text unchanged on August 19, 2026, so the count remains contested.

Attached ADUs (additions sharing a wall with the house) and conversions of existing space inside the house, an attached garage, or an existing permitted accessory structure are allowed with any proposed or existing primary residence (6156.x.A.1, A.11 to A.13). A new attached ADU is capped at 50 percent of the primary residence's floor area and 1,200 sq ft, but the 50 percent limit never applies to attached units up to 850 sq ft (1,000 sq ft with more than one bedroom). Conversions of existing permitted space carry no size cap and no setbacks beyond fire safety, private wells and septic systems, and under the ministerial track a converted ADU may add up to 150 sq ft to accommodate ingress and egress (6156.x.B.1.a). A JADU of up to 500 sq ft may also be created inside the single-family home, and on existing multifamily buildings non-livable space such as storage rooms, attics, basements or garages may become at least one ADU and up to 25 percent of the existing unit count (6156.x.B.1.c). HCD's July 7, 2026 findings letter adds that a new-construction attached ADU under Gov. Code 66314 must remain available in addition to the 66323 converted unit and JADU, a point the county's re-enacted text (Ord. No. 11016) does not yet state.

Section 6156.x.A.5 caps a detached ADU at 1,200 sq ft regardless of the size of the main home, and A.4 caps an attached ADU at 50 percent of the primary residence up to 1,200 sq ft, except that the 50 percent limit does not apply to attached units up to 850 sq ft (1,000 sq ft with more than one bedroom), matching the Gov. Code 66321(b)(2) floors; detached ADUs may be 25 feet tall (A.10) and JADUs are capped at 500 sq ft. The ministerial state-exempt detached unit of 6156.x.B.1.b (Gov. Code 66323(a)(2)) is limited to 800 sq ft and 18 feet, and conversions of an existing permitted accessory structure carry no size cap while they stay within the existing envelope (A.11, B.2.a); PDS-611 applies the same rule to converting part of the house so long as a portion remains the main residence. How the square footage is measured is disputed: codified A.6 computes floor area from the exterior dimensions of the outside walls, HCD's July 7, 2026 findings letter says the county must state its limits in square feet of interior livable space (Gov. Code 66313(d), 66321(b)(2)-(3), 66323(a)(2)), and the county's handout PDS-611 (Rev. 09/02/2026) already tells applicants to use interior dimensions, while Ord. No. 11016 left A.4 and A.6 unchanged. On August 19, 2026 the Board of Supervisors directed staff to report back within 180 days on raising the 1,200 sq ft cap to 1,400 or 1,600 sq ft or more, by right or through a discretionary permit.

No owner-occupancy requirement applies to ADUs: Section 6156.x contains none, the county's ADU ordinance project page states 'The county does not require owner occupancy for ADUs', and Gov. Code 66315 bars one. JADUs are the exception on paper: the county's text still conditions every JADU on a recorded deed restriction making it legal 'only so long as either the primary residence, or the ADU, is occupied by the owner of record' (6156.x.B.3.a.iii and B.3.k, re-enacted unchanged by Ord. No. 11016 on August 19, 2026; handout PDS-611, Rev. 09/02/2026, repeats it). Since January 1, 2026, however, Gov. Code 66333(b) as amended by AB 1154 requires owner occupancy only when the JADU shares sanitation facilities with the house, 66339.5 makes the state JADU article supersede conflicting local ordinances, HCD's July 7, 2026 findings letter directs the county to delete the 'considered legal' language on exactly that ground, and the county's January 29, 2025 Director's Determination says state law prevails, so a JADU with its own bathroom carries no owner-occupancy requirement under operative law. Separately, since September 18, 2026 each buyer of a separately sold ADU condominium must sign a recorded affidavit that they or a family member will live in it as a primary residence for at least one year (6156.x.D.11).

Section 6156.x.A.20 requires one parking space per ADU, which may sit in setbacks or as tandem parking in an existing driveway, and a garage, carport or covered space demolished or converted for an ADU need not be replaced. A.21 waives the space for ADUs within one-half mile of public transit, in an architecturally and historically significant historic district, that are part of the proposed or existing primary residence or an accessory structure, where on-street permits are required but not offered to the occupant, within one block of a car-share vehicle, or filed together with a new single-family or multifamily dwelling. The county's handout PDS-611 (Rev. 09/02/2026) accordingly says a space is only required for a proposed detached ADU and none for an ADU of 800 sq ft or less, consistent with Gov. Code 66323(b), which bars unauthorized standards on state-exempt units. JADUs need no additional parking (B.3.i), but the county text (B.3.h, re-enacted by Ord. No. 11016) and PDS-611 still require the lot's required spaces (two for the house) to be replaced when a garage, carport or covered space is converted or demolished for a JADU; HCD's July 7, 2026 findings letter says that replacement amounts to additional parking barred by Gov. Code 66334 and directed the county to remove B.3.h, and 66339.5 makes the state JADU article control.

ADUs and JADUs are approved ministerially through a building permit from Planning & Development Services, with no discretionary review or hearing: 6156.x.A sets objective criteria, 6156.x.B provides ministerial approval of the Gov. Code 66323 unit combinations in residential and mixed-use zones, and Gov. Code 66317 (15-business-day completeness check, 60-day decision) governs. The county's January 29, 2025 Director's Determination, interpreting Zoning Ordinance Section 1012, directs staff to follow mandatory state housing law wherever the Zoning Ordinance conflicts. The codified text still says ministerial review is unavailable for a JADU attached to an ADU (B.3.g, re-enacted by Ord. No. 11016), but HCD's July 7, 2026 findings letter says any JADU consistent with state law must be considered ministerially and directed the county to delete that line, which Gov. Code 66335 and 66339.5 support. Real exceptions: in the small unincorporated Coastal Zone (Part Nine, around San Elijo Lagoon and San Dieguito) a Coastal Administrative Permit or Coastal Development Permit is also needed because the Section 9404.c exemption for improvements to single-family homes excludes 'self-contained residential units', although Gov. Code 66329(a) bars required hearings for ADU coastal permits and sets a 60-day decision; accessory structures attached to an ADU beyond the 6156.g allowances need an Administrative Permit (A.7); and separate sale requires a Tentative Parcel Map or Tentative Map (6156.x.D).

ADUs may be rented separately from the main home, but 6156.x.A.3, B.2.c and B.3.k bar rental terms of less than 31 days for ADUs and JADUs alike, so short-term rentals are not allowed in them; the county has no short-term-rental permit program, only Transient Occupancy Tax registration for stays of 30 consecutive days or less elsewhere (County Code §§ 22.202(c) and 22.206, whose certificate 'is not a permit to operate'). Separate sale is allowed only (1) as a condominium under the AB 1033 program of Ord. No. 10986 (adopted March 4, 2026, effective April 4, 2026; 6156.x.D requires a Davis-Stirling condominium created by Tentative Parcel Map or Tentative Map, a final inspection, lienholder consent, utility notification, DEHQ and fire-district sign-off, and HOA authorization in planned developments), (2) through an SB 9 two-lot split giving each dwelling its own lot, or (3) under the Gov. Code 66341 qualified-nonprofit path (6156.x.C). Ord. No. 11016 (adopted August 19, 2026, effective September 18, 2026) added three sale rules for ADU condominiums: a right of first refusal held by a rent-paying tenant or co-owner on the lot with 30 days to match any offer, a recorded affidavit that each new buyer or a family member will occupy the unit for at least one year, and a 30-day public MLS listing aimed at owner-occupant buyers (6156.x.D.10 to D.12). JADUs can never be sold separately from the house (B.3.a.i).