Zone 0 in California: AB 3074 defensible space requirements.

Why California has Zone 0 and most states don't

California's wildfire problem is a particular combination of climate, fuel, wind, and the wildland-urban interface (WUI) — the pattern of homes built into wildland. The state writes some of the most aggressive wildfire mitigation rules in the country because the consequences are some of the most catastrophic. AB 3074 Zone 0 is the latest layer in that framework, added on top of the existing 100-foot defensible space requirement codified in California Public Resources Code §4291.

Zone 0 was designed specifically to address the failure mode California fires have shown again and again: a home survives the flame front passing through the wildland, but an ember lands in bark mulch against the foundation or a pine-needle drift in a gutter — and the structure ignites from the perimeter.

Which California counties Zone 0 applies to

AB 3074 Zone 0 applies to homes in designated Very High Fire Hazard Severity Zones (VHFHSZ). The Office of the State Fire Marshal publishes the official Fire Hazard Severity Zone map for every property in the state. Counties with substantial VHFHSZ acreage fall into a few major regional clusters:

Southern California

Los Angeles, San Diego, Orange, Riverside, San Bernardino, Ventura, Santa Barbara. The largest population centers exposed to Zone 0. LA and San Diego counties together contain millions of homes in or adjacent to VHFHSZ areas. The 2017–2018 SoCal fires (Thomas, Woolsey, Lilac) and the 2025 Eaton/Palisades fires are the events that most directly drove the political will behind AB 3074's passage.

Bay Area and North Coast

Sonoma, Napa, Marin, Alameda, Contra Costa, Lake, Mendocino, Solano. The 2017 Tubbs, 2018 Camp, and subsequent Bay Area fires drove some of the strictest local defensible space ordinances in the country — Marin County in particular has been an early adopter of Zone 0-like requirements at the local level even before the state rulemaking finished.

Sierra foothills and Gold Country

Placer, El Dorado, Nevada, Tuolumne, Calaveras, Amador, Mariposa. The foothill counties carry some of the highest per-home risk in the state — dense fuel, narrow access roads, and aging housing stock from the original Gold Country development.

North state

Butte, Shasta, Trinity, Siskiyou, Plumas. Paradise (Butte County) lost in the 2018 Camp Fire. The rebuilt Paradise — and the surrounding north-state communities — are now some of the country's most carefully rebuilt-to-Zone-0 housing stock.

Central Coast and Central Valley pockets

Monterey, San Luis Obispo, Tulare, Madera, Fresno. Smaller VHFHSZ footprints, but real exposure — especially in the foothill-adjacent areas.

State law vs local ordinances

California fire code lets local jurisdictions adopt stricter rules than the state baseline. The result is a patchwork: the AB 3074 Zone 0 framework is the statewide minimum, but many cities and counties have layered their own ordinances on top.

A few examples of stricter local rules already in force:

• Marin County has had a Zone 0-equivalent local ordinance since 2021, ahead of the state rulemaking process.
• Lafayette, Orinda, and Moraga (Contra Costa) have adopted defensible space rules that combine the state framework with WUI building code overlays.
• City of San Diego has issued homeowner guidance setting a February 2027 voluntary Zone 0 compliance target ahead of the state.
• City of Pasadena is targeting a 2029 existing-home compliance date.

The practical implication: even if you're not in a state VHFHSZ, check your local fire department's defensible space ordinance. The local rule may already apply.

What California's fire ecology means for Zone 0

Zone 0 was written for California-specific wildfire behavior. Four characteristics of California fire make the 5-foot ember-resistant zone particularly important:

1. Mediterranean drying. California's summer-fall fire season produces extremely low fuel moisture — chaparral and grass loads burn explosively, and the airborne ember load during a wind event is unusually high.
2. Predictable wind events. Santa Ana (Southern California, fall) and Diablo (Bay Area, fall) winds drive embers downwind for miles. Embers in a 15–40 mph wind event are the dominant ignition mechanism for California home loss, not flame contact.
3. Wildland-urban interface density. California has roughly 4.5 million homes in or adjacent to the wildland-urban interface — the highest density in the country. The aggregate ember exposure across the WUI is extraordinary.
4. Fuel accumulation from suppression. Decades of fire suppression have produced unusually heavy fuel loads in many California wildlands. When those fuels burn, they produce fires more intense than the historical baseline — which generates more embers per acre.

Where California enforcement is heaviest right now

State-level CAL FIRE enforcement is uneven by county. The most consistent enforcement today comes from:

• Insurance carriers — universal across California. Carriers use aerial imagery at renewal in every county; non-renewals tied to defensible space are happening in every region.
• Marin, Sonoma, Napa, and parts of the East Bay — the most active local fire-department inspection programs.
• LA County (especially the western foothills) and Orange County canyons — heavy post-fire scrutiny since 2017–2018; rebuilt areas have very active inspection programs.
• Sierra foothills (Placer, El Dorado, Nevada) — active CAL FIRE inspection programs running April through September.
• Point-of-sale across the state — listing a home in a VHFHSZ now commonly triggers a defensible space inspection requirement.

What to do if you're in California Zone 0 territory

Three actions move every California homeowner forward:

1. Look up your property on the official FHSZ viewer. Office of the State Fire Marshal viewer →
2. Run the free Zone 0 readiness check. The 12-item framework against your property, with the gaps listed and an estimated cost range. Start the check →
3. Check your local fire department's ordinance page. If your jurisdiction has adopted stricter Zone 0 rules, those apply on top of (or ahead of) the state framework.

Status as of May 2026. California Board of Forestry rulemaking and local ordinances continue to evolve. Sources: California Public Resources Code §4291, Office of the State Fire Marshal Fire Hazard Severity Zone Maps, CAL FIRE public documents, and local jurisdiction fire-code adoption records.