Reference
The Zone 0 glossary
Zone 0 / ember-resistant zone
The first five feet measured outward from a structure (the exterior wall, roof edge, attached deck, stairs or pergola), extending five feet or to the property line, whichever comes first. Created in statute by AB 3074 (2020); the statewide implementing regulation was adopted August 19, 2026 and is not yet in effect. Full explainer.
Zone 1 / Zone 2
California's existing defensible space layers under PRC §4291: Zone 1 is 0–30 feet ("lean and green"), Zone 2 is 30–100 feet ("reduced fuel"). Zone 0 layers on top as the strictest innermost band.
AB 3074
The 2020 California law that amended Public Resources Code §4291 to require an ember-resistant zone within five feet of a structure, "based on regulations promulgated by the board." Those regulations are the Zone 0 rule the Board approved on August 19, 2026, which is not yet in effect.
Board of Forestry and Fire Protection
The state board that writes the Zone 0 regulations. It missed the December 31, 2025 deadline set by Executive Order N-18-25, then approved the statewide Zone 0 regulation on August 19, 2026. Approval is not the effective date; Office of Administrative Law review comes next. Tracker.
SRA: State Responsibility Area
Land where the state (CAL FIRE) is financially responsible for wildfire protection, about 31 million acres. The adopted Zone 0 regulation applies to all of it, every hazard class, under PRC §4291, once it takes effect. Check your coverage.
LRA: Local Responsibility Area
Land where a city, county, or district is responsible for fire protection. The adopted Zone 0 regulation reaches the LRA only in Very High Fire Hazard Severity Zones, under Gov. Code §51182. Its LRA track (§1298.04) is worded differently from the SRA track (§1299.03): only the LRA version bars new combustible fencing run "parallel" to the structure, and the SRA version keys to a "Building or Structure" rather than an "Occupied Structure."
FHSZ: Fire Hazard Severity Zone
CAL FIRE's hazard classification (Moderate, High, Very High) based on fuels, terrain, weather and ember production. LRA maps were redrawn February–March 2025, the first update since 2011. Check your address.
Noncombustible
Under the adopted statewide regulation, carried over unchanged from the July 2026 draft: a material that passes the ASTM E136 test. In practice aluminum, steel, wrought iron, chain link, masonry, concrete, and stone. Not the same as "fire-resistant," "fire-rated," or "Class A." Materials guide.
ASTM E136
A vertical tube furnace test at 750 °C measuring whether a material itself can burn or add fuel. The regulation's definition of noncombustible. Wood, vinyl, composite, and fire-retardant treated wood all fail it.
ASTM E84 / "Class A"
A tunnel test of surface flame spread designed for interior finishes. A "Class A" rating is not noncombustibility and does not satisfy the regulation's fence material standard, a distinction some marketing blurs.
FRTW: Fire-retardant treated wood
Wood pressure-treated with fire retardants. It slows ignition but does not pass ASTM E136, so it does not qualify under the adopted state regulation. San Diego's local ordinance allows OSFM-listed FRTW in one narrow case (new parallel fencing).
Occupied Structure (regulation term)
The term used in the Local Responsibility Area track for the buildings that trigger Zone 0 obligations; the State Responsibility Area track says "Building or Structure" instead. The fence provisions run from the Occupied Structure and its attachment points. The August 19, 2026 package narrowed the definition: an attached deck, stairs or pergola counts as part of the structure, and only patios made of noncombustible materials are excluded.
Noncombustible span / transition span
The five feet of fence nearest the structure, in noncombustible material, required by the adopted regulation (in both the LRA and SRA tracks) where a fence or gate attaches to (or comes within one foot of) the structure. Anatomy of the span.
Defensible space
The buffer of managed vegetation and materials around a structure required by PRC §4291 (100 feet in the SRA). Zone 0 is its innermost, strictest band.
WUI: Wildland-Urban Interface
Where development meets wildland fuels. California's WUI building code (Title 24 Part 7) is where the regulation's noncombustibility reference standard lives.
Safer from Wildfires (10 CCR §2644.9)
The 2022 insurance regulation requiring insurers that price wildfire risk to credit twelve mitigation measures. Noncombustible fences and gates within five feet is listed first on carrier certification forms. It binds insurers, not homeowners. Insurance guide.
Rating vs. underwriting
Rating = how a premium is calculated (the §2644.9 credits live here). Underwriting = whether a carrier will write or renew the policy at all. A required credit is not a coverage guarantee. The Board itself says Zone 0 compliance "won't guarantee insurance."
IBHS Wildfire Prepared Home
A voluntary, inspected designation from the Insurance Institute for Business & Home Safety requiring (among other things) noncombustible fencing within five feet, with vinyl explicitly banned. Some carriers tie discounts or renewal commitments to it. Details.
FAIR Plan
California's insurer of last resort. Offers wildfire hardening discounts (up to 16.4% on the wildfire portion for dwelling policies) naming fences and gates within five feet.
OAL: Office of Administrative Law
The state office that reviews and files regulations. This is where the Zone 0 rule sits now: the Board approved it on August 19, 2026, and it takes effect only after OAL reviews the package (a five-day public comment period is provided during that review) and the Secretary of State publishes it. That review is the gap between "adopted" and "effective," and it is why no statewide deadline is running yet.
Emergency rulemaking
The accelerated OAL review pathway created by AB 1455 (2025). Board staff said they would submit the Zone 0 package this way immediately upon approval, which is why staff expected the rules "could become effective as early as September 2026." That is an expectation, not a scheduled date: no effective date exists until OAL completes its review.
Phase 1 / Phase 2 (compliance phases)
The regulation's runway for existing homes. Some items are due on the effective date itself, including roof and gutter debris (moved up in the August package) and the tree-maintenance items already required by statute. Phase 1 (within 3 years) covers combustible materials, mulch, debris and firewood; Phase 2 (3 years, or up to 5 on a local fire agency's timeline) covers vegetation buffers, fences, gates, and outbuildings. New construction complies from the effective date, which does not exist yet. Timeline.
Ember cast / ember attack
Wind-driven embers landing ahead of a fire front. This is the ignition mechanism behind most home losses, and the scientific basis for the five-foot zone. The fire science.
Missing a term you've seen in a mailer or an ordinance? Tell us. If it's real, we'll define it; if it's marketing, we'll say that too.