Los Osos

San Luis Obispo County portion

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ADU Pass helps homeowners in Los Osos, San Luis Obispo County, California navigate the permit paperwork for building an accessory dwelling unit. This area covers 1 ZIP code.

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San Luis Obispo County — county ADU rules and overlays

County ADU ordinance

San Luis Obispo County (population ~283,000) sits on the central California coast between Monterey County to the north and Santa Barbara County to the south. The county seat is San Luis Obispo (~47,000); the largest city is Paso Robles (~32,000); other incorporated cities are Atascadero, Arroyo Grande, Pismo Beach, Morro Bay, and Grover Beach. The unincorporated population is large and dispersed: Nipomo (~17,000), Los Osos / Baywood Park (~14,000), Templeton (~7,700), Cambria (~5,800), Oceano (~7,500), Avila Beach, Cayucos, Creston, Santa Margarita, Pozo, San Miguel, Shandon, San Simeon, Harmony, Cholame, and many smaller wine-country and coastal hamlets. The Hearst Castle / Hearst San Simeon State Historical Monument anchors the north coast; Diablo Canyon Nuclear Power Plant (PG&E) sits at Diablo Cove south of Avila Beach, with extended operations through 2030 (Sen. Bill 846, 2022) preceding decommissioning. Vandenberg SFB extends into the southern county along the coast. The county Board of Supervisors administers ADU permitting in unincorporated territory under California Government Code Sec. 65852.2 (state ADU preemption) and Sec. 65852.22 (JADU preemption), overlaid by California Coastal Commission jurisdiction along the coast and Airport Land Use Commission (ALUC) overlay across the entire county.

State-floor overlay: California state ADU preemption applies in full to all unincorporated parcels. Coastal Zone parcels still require a Coastal Development Permit (or an appealable equivalent under the certified Local Coastal Program) on top of the state-floor ministerial review; ADUs that fit within an LCP-defined exempt or de minimis category may avoid CDP appeal exposure. ALUC overlays do not preempt the state ADU regime but layer compatibility review (noise, safety, height) on top. AB 976 prohibits owner-occupancy mandates on detached ADUs. AB 2221 / AB 2533 (2022-2023) further constrain local denial grounds.

County regulatory overlays

San Luis Obispo County overlays of consequence: California Coastal Zone with certified Local Coastal Program (Title 23) covering Cambria, San Simeon, Cayucos, Los Osos / Baywood Park, Avila Beach, Pismo Beach (incorporated), Oceano, and Nipomo Mesa; Airport Land Use Commission overlays for SLO Regional Airport, Paso Robles Municipal, Oceano County, and the Diablo Canyon ISFSI airfield; Diablo Canyon Nuclear Power Plant Emergency Planning Zone (10-mile EPZ); Hearst Castle / Hearst San Simeon State Historical Monument (state landmark + National Register); Vandenberg Space Force Base extending into southern SLO County; Hosgri Fault Zone (offshore) and San Simeon Thrust Fault Zone (Alquist-Priolo); CAL FIRE State Responsibility Area on the Santa Lucia Range and inland foothills; FEMA SFHA along the Salinas River, Estrella River, Arroyo Grande Creek; Williamson Act / agricultural preserves in Paso Robles wine country and Edna Valley; Carrizo Plain National Monument in the southeast (federal BLM); the Pinnacles eastern environs / Salinas River corridor scenic designations; and the Morro Bay National Estuary federal designation.

County permitting (unincorporated parcels)

The San Luis Obispo County Department of Planning and Building issues ADU permits for unincorporated parcels including Nipomo, Los Osos / Baywood Park, Templeton, Cambria, Oceano, Avila Beach, Cayucos, Creston, Santa Margarita, Pozo, San Miguel, Shandon, San Simeon, Harmony, Cholame, and the wine-country and coastal hamlets. Practical permitting frictions: Coastal Zone Local Coastal Program review on coastal unincorporated parcels (Cambria, San Simeon, Cayucos, Los Osos, Avila, Oceano, Nipomo Mesa); ALUC compatibility review on parcels within airport influence areas (San Luis Obispo Regional, Paso Robles Municipal, Oceano County, Diablo Canyon ISFSI airfield); CAL FIRE State Responsibility Area on the Santa Lucia Range and inland foothills with Very High FHSZ designations; FEMA SFHA along Salinas River, Estrella River, Arroyo Grande Creek, San Luis Obispo Creek, Santa Rosa Creek; Coastal Zone septic regulations (post-Los Osos sewer-mandate experience); seismic zones (Hosgri Fault offshore, San Andreas inland, San Simeon thrust); and Diablo Canyon Emergency Planning Zone overlay extending ~10 miles around the plant site.

DepartmentSan Luis Obispo County Department of Planning and Building

Address976 Osos Street, Room 300, San Luis Obispo, CA 93408

Phone805-781-5600

California state — ADU law and programs

State ADU law

California has the most aggressive statewide ADU preemption regime in the US, built from ~15 bills passed 2019-2025 and enforced by the Department of Housing and Community Development (HCD). The 2026 HCD ADU Handbook addendum (in effect with the 2025 Title 24 code cycle) is the operative state-level reference. The regime does four things at once: (1) preempts local zoning that would ban or unreasonably restrict ADUs; (2) imposes by-right ministerial approval with short statutory deadlines; (3) caps fees and utility-connection charges; and (4) empowers HCD to void non-compliant local ordinances.

State HOA preemption

California has the strongest statewide HOA-preemption regime in the US for accessory dwelling units, built from two bills: AB 670 (2019) voided ADU-prohibiting covenants on single-family residential lots, and AB 3182 (2020) extended and codified the preemption into the Davis-Stirling Common Interest Development Act (Civil Code §§ 4740 / 4741). The combination prohibits common-interest communities from banning ADUs, restricting rentals below 25% of separate interests, or treating ADUs as separate HOA interests. Limits remain: HOAs retain authority over reasonable design standards and statutory height limits, and the 2026 Carlsbad case (CalMatters coverage) established that an HOA's documented design-standards regime can effectively delay or constrain ADU approval short of outright prohibition.

State financing programs

California's flagship state-level ADU financing program — the CalHFA ADU Grant Program — is paused and has not been refunded since the original $100 million allocation was fully deployed 2023-12-28. The program provided up to $40,000 per qualifying homeowner for pre-construction and non-recurring closing costs and financed approximately 2,500 ADUs in two rounds. As of 2026-04, no new funding round has been announced in the state budget. CalHFA continues to publish anti-scam warnings because bad actors actively solicit homeowners claiming access to grant funds that no longer exist. State-level financing activity has shifted to local pilot programs (San Francisco, San Jose, Los Angeles, San Diego) and private financing products (Fannie Mae ADU mortgage, HELOC, construction-to-permanent).

CalHFA ADU Grant Program
HCD ADU Funding index

State housing programs

California's state-level ADU programs are concentrated at HCD (technical guidance, ordinance review, enforcement) and the paused CalHFA grant pipeline (covered under stateFinancing). The state does not operate a central pre-approved ADU plan library — instead, AB 1332 (2024) created a preemption framework for local pre-approved plans with a 30-day ministerial-approval deadline, and major cities (Los Angeles, San Diego, San Jose, Sacramento, Berkeley) have rolled out their own plan catalogs. The California YIMBY coalition and other housing-policy organizations play an influential role in bill drafting; they are not state agencies but effectively drive much of the ADU legislative agenda. The Title 24 code cycle (now 2025, in effect for 2026 permits) is the authoritative building-code baseline.

Federal (United States) — ADU-relevant rules and programs

Federal ADU law

The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.

Federal financing programs

Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.

Federal tax credits

There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.

Federal housing programs

HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.

ZIP Code

93402

Post Office

1189 Los Osos Valley Rd, 93402