Santa Clarita

Los Angeles County regulates ADUs on unincorporated parcels under Title 22 (Planning and Zoning) of the County Code. The ordinance layers on top of California Government Code sections 65852.2 (ADU) and 65852.22 (JADU) and conforms to AB 68 / AB 881 / SB 13 (2019), AB 345 / AB 976 (2019 owner-occupancy elimination), AB 2221 / SB 897 (2022 permit-timeline tightening), and AB 1033 (2023 optional condo-ADU separation). Per ongoing state ADU reform — including AB 976 (2023 permanent elimination of owner-occupancy requirements), AB 1033 (2023 condo-ADU), AB 2533 (2024 strengthened amnesty / unpermitted-ADU legalization), SB 543 (2024 fee transparency), and AB 1332 (2023 statewide pre-approved plans) — any local provision conflicting with state law is null and void. The county's distinct contributions atop state law are its Hillside Management Area (HMA) design standards, Very High Fire Hazard Severity Zone (VHFHSZ) / WUI requirements for extensive back-country parcels, Coastal Development Permit (CDP) requirements in the certified portions of the county's Local Coastal Program (Santa Monica Mountains, Marina del Rey, and unincorporated coastal fringe), historic-district protections in designated Historic Preservation Overlay Zones and National Register districts, and airport-noise compatibility review around Whiteman, Compton/Woodley, Fox Field, General Fox, and the military influence areas.

• Los Angeles County Code Title 22 (Planning and Zoning), Section 22.140.640 — Accessory Dwelling Units
• Los Angeles County Code Title 22 Section 22.140.645 — Junior Accessory Dwelling Units
• Ordinance No. 2020-0019 — Initial comprehensive ADU ordinance conforming to 2019 state reform package
• Ordinance No. 2023-0041 — ADU Ordinance Update
• County Planning ADU program webpage and technical bulletins

State-floor overlay: California state law (Gov. Code 65852.2, 65852.22) preempts most local ADU regulation. The state sets ministerial-approval requirements; caps owner-occupancy restrictions (permanently eliminated by AB 976, effective 2024); mandates 60-day permit review timelines (AB 2221 / SB 897); sets minimum allowed sizes (state-floor 850 sqft one-bedroom, 1000 sqft two-bedroom for detached ADUs); forbids parking requirements within 1/2 mile of transit or for ADUs created via garage conversion; caps impact fees at zero for ADUs under 750 sqft (SB 13); requires utility connection handling (AB 2221 / SB 897 prohibit separate sewer/water capacity fees for ADUs under certain thresholds); and preempts local design-review triggers beyond objective design standards. AB 2533 (2024) requires jurisdictions to administratively legalize pre-2020 unpermitted ADUs that meet current state standards. AB 1033 (2023) permits — but does not mandate — cities and counties to opt into an optional program allowing ADUs to be sold as condominium units separately from the primary dwelling. Los Angeles County's ordinance reiterates and applies these state floors, adding only the locally-controlled hillside, fire, coastal, historic, and airport-noise overlays. Where a project is in a VHFHSZ, the Santa Monica Mountains Local Coastal Program jurisdiction, or a Historic Preservation Overlay Zone, state ADU preemption still applies to the ADU allowance itself but does not preempt the county's separate fire, coastal, or historic-preservation authority over site-design standards.

Los Angeles County administers or co-administers an unusually wide set of overlay regimes that materially affect ADU siting on unincorporated parcels, reflecting its combined coastal, mountain, desert, and urban geography: (1) California Coastal Commission jurisdiction in the unincorporated coastal zone, implemented through the county's certified Local Coastal Programs for the Santa Monica Mountains (Malibu/Topanga area) and Marina del Rey; (2) Very High Fire Hazard Severity Zones (VHFHSZ) designated by CAL FIRE / State Board of Forestry across the Angeles, San Gabriel, and Santa Monica Mountains and the Antelope Valley foothills, driving California Building Code Chapter 7A (WUI) ignition-resistant-construction and Pub. Res. Code 4291 defensible-space requirements; (3) Hillside Management Areas (HMA) defined under Title 22 on parcels with slope 25% or steeper — a county-unique overlay that adds objective hillside design standards on top of state ADU allowance; (4) FEMA Special Flood Hazard Areas along the Los Angeles, San Gabriel, Rio Hondo, Santa Clara, and Antelope Valley washes, administered by DPW through the county Floodplain Management program; (5) Historic Preservation Overlay Zones and National Register districts — most concentrated in Altadena, Florence-Firestone, East Los Angeles, and specific unincorporated historic enclaves — where design review applies; (6) Airport Land Use Compatibility Plans administered by the Los Angeles County Airport Land Use Commission for Whiteman (Pacoima), Compton/Woodley, Fox Field (Lancaster), General Fox, Brackett Field (La Verne), San Gabriel Valley, Catalina (Avalon), plus military AIAs around Los Alamitos JFTB, Point Mugu, and the Edwards AFB southern extensions; (7) the Santa Monica Mountains North Area Community Standards District and other Community Standards Districts (CSDs) that add area-specific objective standards on top of the base zone.

• California Coastal Commission / Santa Monica Mountains and Marina del Rey Local Coastal Programs — State law (Gov. Code 65852.2(j)) preserves the CDP requirement for ADUs in the Coastal Zone notwithstanding otherwise-ministerial ADU preemption. The ADU itself is still allowed by right; the site-specific CDP review addresses visual, habitat, and public-access impacts separately. The Santa Monica Mountains LCP imposes the most distinctive overlay-specific restrictions on ADU siting in LA County — including ridgeline-avoidance setbacks, ESHA buffer requirements, and fuel-modification-zone coordination with LACoFD.
• CAL FIRE / LACoFD Very High Fire Hazard Severity Zones and Hillside Management Area Fire Requirements — The 2025 wildfire season reinforced fire-hardening requirements across the county. LACoFD may impose additional project-specific conditions in post-fire rebuild areas (Eaton Fire / Palisades Fire rebuild zones). Note: the 2024 'Fire Hazard Severity Zone' statewide update (effective 2025) expanded LRA VHFHSZ boundaries in many LA County unincorporated communities; owners should verify current designated status via the OSFM / CAL FIRE web map. The WUI Chapter 7A premium commonly adds 8-15% to ADU construction cost in unincorporated VHFHSZ communities.
• Hillside Management Area (HMA) — Title 22 objective design standards for sloped parcels — The HMA overlay is largely unique to LA County among California counties of comparable size and often governs the buildable-envelope question before the ADU allowance question. Owners should retain a civil engineer early to verify buildable envelope within HMA constraints; an ADU is still allowed as of right under state law but may be limited to the existing dwelling footprint (conversion) where hillside-envelope constraints preclude a detached addition.
• FEMA Special Flood Hazard Areas — National Flood Insurance Program — Mandatory flood insurance applies to ADUs in SFHA with federally-backed mortgages. Owners should verify effective FIRM panel status before design. Post-2025 wildfire burn scars in the Santa Monica and San Gabriel mountains have elevated debris-flow risk and may result in emergency or post-event FIRM revisions.
• County Historic Preservation — HPOZ-equivalent protection and National Register districts — ADUs within the footprint of a designated historic structure (attached, conversion, JADU) trigger historic-review for building-envelope modifications. Detached ADUs on historic parcels are generally less restricted as long as they are visually subordinate and set back from the historic structure. National Register listing by itself does not impose private-property regulatory limits; it becomes enforceable only when federal funding or permits are involved — but local HPOZ-equivalent designation does impose objective design review.
• LA County Airport Land Use Commission — ALUCP review — In a safety-zone inconsistency, the Board of Supervisors may override only by super-majority vote per PUC 21676. Most single detached ADUs outside the innermost safety zones face only noise-attenuation requirements; ADUs in Safety Zone 1 (runway protection zone) may be prohibited, and those in Safety Zones 2-3 may face density limits that preclude new dwelling units.
• Community Standards Districts (CSDs) — area-specific objective design overlays — CSD standards must remain objective under state ADU preemption. Any CSD provision that would turn a ministerial ADU into a discretionary project or impose non-objective design review is null and void as to ADUs. Applicants and reviewers should cross-reference base zone, CSD, HMA, HPOZ, CDP, and ALUC layers for any given parcel via GIS Net before design.

The Los Angeles County Department of Regional Planning (DRP) is the lead planning / zoning authority for ADU applications on unincorporated parcels, working in tandem with the Department of Public Works — Building and Safety Division (DPW B&S) for building-code plan check and inspection, the Los Angeles County Fire Department (LACoFD — which also serves most contract cities) for fire-defensible-space and WUI review, and the county's Department of Public Health (DPH Environmental Health) where on-site septic or well-water systems are involved. Unincorporated Los Angeles County is vast and diverse: it covers approximately 2,650 square miles and includes dense urbanized fringe areas (East Los Angeles, Florence-Firestone, Willowbrook, West Rancho Dominguez, West Whittier-Los Nietos, Hacienda Heights, Rowland Heights, Altadena, La Crescenta-Montrose, Ladera Heights, View Park-Windsor Hills, Marina del Rey), suburban communities (Walnut Park, Topanga, Agua Dulce, Acton), and extensive rural back-country (Antelope Valley unincorporated — Leona Valley, Littlerock, Llano, Lake Hughes, Green Valley; Angeles and San Gabriel National Forest fringe; Santa Monica Mountains; Santa Clarita Valley unincorporated fringe). ADU permit review therefore traverses materially different zoning, fire-hazard, and overlay regimes depending on where the parcel sits.