San Diego County

The County of San Diego Planning & Development Services (PDS) department is the single-point-of-contact for ADU permits on parcels in the unincorporated county. Unincorporated San Diego County covers approximately 3,570 square miles (about 79% of the county's 4,526 sqmi land area) and includes densely developed fringe areas (Ramona, Alpine, Lakeside, Spring Valley, Fallbrook, Valley Center), rural back-country (Julian, Warner Springs, Jacumba, Boulevard, Campo), and tribal lands (which are not county-permitted). The 18 incorporated cities (San Diego, Chula Vista, Oceanside, Escondido, Carlsbad, Vista, San Marcos, El Cajon, Santee, La Mesa, Encinitas, National City, Poway, Coronado, Imperial Beach, Lemon Grove, Del Mar, Solana Beach) permit their own ADUs independently. PDS combines planning / zoning review, building plan review, grading / drainage review, fire-district referral (most unincorporated areas are served by CAL FIRE / County Fire Authority or a local Fire Protection District rather than a city fire department), and environmental review (CEQA applicability is normally exempt for ministerial ADUs per Gov. Code 65852.2(f) and Pub. Res. Code 21080(b)(8)).

Process overview: ADU approval in unincorporated San Diego County is a ministerial combined zoning / building / fire / environmental review. Typical sequence: (a) applicant completes the PDS pre-application checklist on the ADU webpage and verifies parcel zoning via the county's parcel lookup and zoning map (Z-maps); (b) applicant submits an ADU Building Permit application through Accela with site plan, floor plans, elevations, Title 24 energy compliance documentation, structural plans (for detached), and a Fire Safety Element attestation if the parcel is in a VHFHSZ; (c) PDS zoning confirms ADU type eligibility, size, setbacks, height, and any overlay triggers (ALUC, CDP, historic, biological); (d) PDS building / plan check reviews for California Building Code, California Residential Code, California Energy Code, and CALGreen compliance; (e) CAL FIRE or the local FPD reviews for defensible space, water supply (minimum fire flow), and access (driveway width, turnarounds) for parcels outside hydranted water; (f) the San Diego Regional Airport Authority ALUC reviews ADUs within ALUCP safety or noise zones; (g) if the parcel is in the County LCP coastal zone, the applicant obtains either an Administrative CDP (most single ADUs) or a CDP heard by the Zoning Administrator; (h) permit issuance, construction, inspections, certificate of occupancy. The ministerial 60-day clock (Gov. Code 65852.2(b)) starts on application acceptance as complete; overlay-triggered sub-reviews (CDP, ALUC) are subject to their own statutory timelines and do not extend the ADU review itself beyond state limits.

Impact fees: San Diego County aligned its impact-fee schedule to SB 13 (2019). ADUs under 750 sqft are exempt from all county impact fees (Traffic Impact Mitigation, Park Lands Dedication, Fire Mitigation, Library Mitigation, Regional Transportation Impact Fee). ADUs 750 sqft or larger pay impact fees proportional to their size as a fraction of the primary dwelling. Building-permit fees, plan-check fees, and fire-district review fees are separate from impact fees and apply at cost-recovery rates regardless of ADU size. Sewer (Metropolitan Wastewater District, Padre Dam, or on-site septic), water (Sweetwater, Otay, Helix, Padre Dam, Rincon del Diablo, Rainbow, Fallbrook, Ramona, San Dieguito, Santa Fe Irrigation, Valley Center, Yuima, or on-site well), and school fees (Ramona USD, Escondido Union, Fallbrook Union, Mountain Empire, Valley Center-Pauma, etc.) are administered by the respective district authorities, not the county. A 750-sqft-ceiling ADU is the dominant cost-minimization design in unincorporated San Diego County because of the hard impact-fee cutoff. (schedule)

The San Diego County Assessor/Recorder/County Clerk (ARCC) maintains parcel-level assessment records for all real property in San Diego County, including parcels inside all 18 incorporated cities. California is a statewide Proposition 13 jurisdiction: real property is assessed at the lower of (a) factored base-year value (1975 or last change-in-ownership / new-construction value, escalated at the lesser of 2% or CPI annually) or (b) current fair market value under Prop 8. An ADU is treated as new construction on the host parcel: the ADU itself receives a supplemental assessment at its construction-cost fair-market value as of completion date, while the primary dwelling's Prop 13 base-year value is NOT re-triggered. The supplemental assessment is prorated from the completion date through the end of the fiscal year and the assessment cycle thereafter. This 'addition only' treatment is the single most important ADU economic fact statewide: owners can add square footage via an ADU without resetting the Prop 13 base of the existing home. California law (Rev. & Tax. Code 74.3) further provides a New Construction Exclusion for ADUs used as a 'principal place of residence' of a parent / child (intergenerational-housing ADU), but the exclusion is narrow and must be elected by timely filing.

Assessment policy: ADU new-construction supplemental assessments are issued after the building permit final inspection, typically within 6 to 12 months of completion (the longer end is common in active-permit-year backlogs). The supplemental tax bill is issued by the county Treasurer-Tax Collector separately from the annual roll bill. For most owner-built 500-800 sqft ADUs in unincorporated San Diego County, typical observed supplemental assessments range from $150,000 to $280,000 of new assessed value (reflecting current construction cost, not finished-home-sale comps), yielding a supplemental annual property-tax increase of approximately $1,500-$2,800 at the combined ~1.05-1.15% effective rate (1% Prop 13 base + local assessments / Mello-Roos). Owners planning an intergenerational ADU should file the Rev. & Tax. Code 74.3 Claim for New Construction Exclusion (Parent/Child ADU) promptly after permit issuance; late filings lose benefit for prior fiscal years.

San Diego County administers or co-administers several overlay regimes that materially affect ADU siting on unincorporated parcels: (1) the California Coastal Commission's jurisdiction along the coastal zone (a narrow band up to 5 miles inland in some places), implemented through the county's certified Local Coastal Program (LCP) covering unincorporated coastal segments; (2) Very High Fire Hazard Severity Zones (VHFHSZ) designated by CAL FIRE and reviewed by the State Board of Forestry, which cover very large portions of the unincorporated back-country and drive defensible-space, ignition-resistant-construction, and access requirements; (3) FEMA Special Flood Hazard Areas (SFHA) along the San Diego River, San Dieguito River, San Luis Rey River, Otay River, Sweetwater River, Tijuana River, and associated coastal zones; and (4) Airport Land Use Compatibility Plans (ALUCP) administered by the San Diego County Regional Airport Authority's Airport Land Use Commission around MCAS Miramar (federal military), NAS North Island / Naval Outlying Landing Field Imperial Beach (federal military), Gillespie Field (Santee, county-owned), McClellan-Palomar (Carlsbad, county-owned), Brown Field (Otay Mesa, City of San Diego), Montgomery-Gibbs Executive (Kearny Mesa, City of San Diego), Ramona Airport (county-owned), Fallbrook Community Airpark (county-owned), Oceanside Municipal, and Jacumba Airport. Seismic-retrofit overlays are not a county-administered regime in San Diego (unlike parts of Los Angeles / San Francisco); California seismic building-code compliance applies statewide through the California Building Code adopted by the county.

• California Coastal Commission / County Local Coastal Program (LCP) — The county's LCP covers the unincorporated coastal segments near Del Mar Mesa, Torrey Pines extensions, Crest / Harmony Grove (tributary areas), and the Camp Pendleton / Oceanside boundary. An ADU within the coastal zone requires a Coastal Development Permit (CDP) unless categorically excluded; most single detached ADUs qualify for an Administrative CDP (noticed but ministerial-like) while those in sensitive-biological or visually-sensitive settings may require a heard CDP. The Coastal Commission retains appeal jurisdiction over county CDPs within the defined appeals area. State law (Gov. Code 65852.2(j)) preserves the CDP requirement for ADUs in the coastal zone notwithstanding the otherwise-ministerial state ADU framework.
• CAL FIRE / State Board of Forestry Very High Fire Hazard Severity Zones (VHFHSZ) and County Fire Code — Very large portions of unincorporated San Diego County — most of the East County back-country including Julian, Warner Springs, Descanso, Pine Valley, Jacumba, Campo, Boulevard, Dulzura, Potrero, Palomar Mountain, Cuyamaca, and the San Diego / Cleveland National Forest interface — are designated VHFHSZ in either the State Responsibility Area (SRA) or the county's Local Responsibility Area (LRA). An ADU in a VHFHSZ must comply with California Building Code Chapter 7A (WUI-rated exterior materials: ignition-resistant siding, dual-pane windows, 1/8-inch-max vent screens, Class A roofing, non-combustible eaves / soffits / decks), minimum 100-foot defensible-space per Pub. Res. Code 4291, minimum driveway width and turnaround per fire-district standards, and minimum fire-flow water supply (2,500 gpm residential standard, reduced for sprinklered ADUs per Sec. R313). CAL FIRE or the local FPD (Alpine, Bonita-Sunnyside, Deer Springs, Julian-Cuyamaca, Lakeside, North County, Pine Valley, Rancho Santa Fe, Rural FPD of San Diego County, Valley Center, etc.) reviews the ADU permit. The 2025 wildfire season reinforced these requirements; no county-wide moratorium has been imposed, but permit backlogs lengthen post-fire when affected areas surge rebuild applications.
• FEMA Special Flood Hazard Areas (SFHA) — National Flood Insurance Program — The county administers FEMA NFIP floodplain regulations for unincorporated parcels. Principal SFHA extents are along the San Luis Rey River (Bonsall, Pala, Pauma), San Dieguito River (Lakeside, Ramona uplands), San Diego River (Lakeside, Santee extensions), Sweetwater River (Spring Valley extensions), Otay River (Jamul, Dulzura, Otay Mesa extensions), and Tijuana River estuary (Tijuana / Imperial Beach extensions). ADUs in an SFHA require lowest-floor elevation to or above Base Flood Elevation plus 1 ft county freeboard, flood vents on enclosures below BFE, anchoring, and a post-construction Elevation Certificate. 2024-2025 saw several FEMA FIRM revision studies for Otay, San Luis Rey, and Sweetwater watersheds; owners should confirm current effective panel before design.
• Airport Land Use Compatibility Plans (ALUCP) — San Diego Regional Airport Authority ALUC — The San Diego County Regional Airport Authority serves as the ALUC for all airports in the county. ALUCP airport influence areas (AIAs) extend roughly 2-5 miles beyond each airport depending on runway configuration and establish safety zones (Zones 1-6) and noise contours (60/65/70 dB CNEL). Principal ALUCP overlays affecting unincorporated parcels are MCAS Miramar (extensive AIA covering Scripps Ranch fringes, Miramar Ranch North, Tierrasanta approaches, into unincorporated Rancho Santa Fe / Poway fringes), Gillespie Field (AIA extending into unincorporated Lakeside, El Cajon fringes, Bostonia), McClellan-Palomar (Carlsbad-adjacent unincorporated areas), Ramona Airport (large rural AIA), and Fallbrook Community Airpark (Bonsall / Fallbrook). An ADU in a safety zone may face density restrictions, CC&R / avigation-easement recording requirements, and noise-attenuation construction standards (STC-rated windows, forced-air HVAC with acoustic treatment). The ALUC reviews county-referred projects; in a safety-zone conflict the county may override only by a super-majority Board vote per PUC 21676.
• San Diego County Biological Mitigation Ordinance / Multiple Species Conservation Program (MSCP) — The county's MSCP covers south county unincorporated areas and establishes Pre-Approved Mitigation Areas and a Biological Mitigation Ordinance that triggers biological review for grading and construction in designated preserve-land overlays. An ADU outside the existing dwelling footprint that requires grading in a designated MSCP preserve or Biological Resource Core / Linkage area will trigger a biological review / mitigation obligation on top of the ministerial ADU permit. Inside a parcel's previously-disturbed building envelope the MSCP typically does not add requirements. The East County MSCP Subarea Plan remains pending final approval as of 2026-04-20.