AB 3074 and Zone Zero: how the new law created the 5-foot ember-resistant requirement.

Before AB 3074: California defensible space without Zone 0

For decades, California defensible space law was structured around a single principle: create a 100-foot buffer of managed vegetation around habitable structures in fire hazard areas, with the goal of stopping the flame front before it reaches the building.

The pre-AB 3074 framework had two zones:

• Zone 1 (5–30 ft) — the “lean, clean, and green” zone. Vegetation allowed but managed: thinned, low, kept free of dead material, well-watered.
• Zone 2 (30–100 ft) — the “reduce fuel” zone. Vegetation thinned and spaced to reduce fire intensity.

Notably absent: any specific rules about the first 5 feet from the structure. Pre-AB 3074, bark mulch could touch the foundation. Wood fences could attach directly to the wall. Container plants of any species were allowed anywhere. The implicit assumption was that if Zones 1 and 2 were properly managed, the area within 5 feet of the house didn't need its own rules.

The finding that changed everything

That assumption turned out to be wrong. Beginning with the 2017 Tubbs Fire and continuing through the 2018 Camp Fire and subsequent California fire seasons, post-fire research consistently documented the same failure mode:

Most homes that burned in California wildfires were not consumed by direct flame contact. They were ignited by wind-blown embers that traveled ahead of the fire front and landed in vulnerable spots adjacent to the home — bark mulch against the foundation, pine needles in gutters, a wood fence attached to the wall.

The Insurance Institute for Business & Home Safety (IBHS), the National Institute of Standards and Technology (NIST), and CAL FIRE's own post-fire investigations all reached the same conclusion: embers, not flames, were the dominant ignition mechanism.

Traditional defensible space — the 100-foot buffer of managed vegetation — works well against flame contact. It works poorly against ember storms, because the embers bypass the buffer entirely and ignite the home directly.

For the underlying fire science in detail, see How Zone 0 Stops Wildfire: The Science of Ember Ignition.

The legislative response: AB 3074

Assemblymember Laura Friedman (D-Glendale) authored AB 3074 in early 2020. The bill was developed in close coordination with CAL FIRE, the California Department of Insurance, fire-mitigation research organizations, and the major California insurance industry associations.

The bill's legislative findings explicitly cited ember-driven home loss in the 2017 Tubbs Fire and 2018 Camp Fire as the basis for needing a new rule. AB 3074's findings section noted that traditional defensible space — Zones 1 and 2 — was insufficient to address the ember failure mode and that an additional layer of protection inside the 5-foot perimeter was necessary.

AB 3074 passed both chambers of the California legislature with broad bipartisan support and was signed by Governor Newsom in September 2020. It became effective on January 1, 2021.

What AB 3074 actually changed in PRC §4291

Mechanically, AB 3074 added a new subsection to California Public Resources Code §4291 that:

1. Created the Zone 0 ember-resistant zone covering the first 5 feet from any wall of a structure in a designated Very High Fire Hazard Severity Zone.
2. Required that the Zone 0 perimeter be ember-resistant — free of materials that can ignite from a wind-blown ember and transmit fire to the structure.
3. Directed the California Board of Forestry & Fire Protection to develop implementing regulations specifying what ember-resistant means in operational terms.

The statutory text deliberately delegated the operational details — exactly which materials qualify, how compliance is verified, what enforcement looks like — to the Board's rulemaking process. The Board has been working on those regulations since 2021. For the current status of that rulemaking, see Zone Zero Regulations.

Why 5 feet specifically

The 5-foot dimension wasn't arbitrary. It came from the empirical fire-research literature, particularly IBHS ember exposure testing. The finding: when a combustible material within 5 feet of a wall ignites from an ember, the resulting small fire is close enough to transfer to the structure's siding via radiation, convection, or direct flame contact. When the same material is more than 5 feet from the wall, the gap is usually large enough that even an ignited element doesn't bridge to the building.

The 5-foot perimeter is therefore the empirically-derived distance at which ember-driven ignition transitions from a ground fire to a structure fire. AB 3074 codified this threshold into California law.

What was added: the 12 Zone 0 requirements

AB 3074's implementing framework — the 12-item compliance list the Board has used in successive rulemaking drafts — addresses each known ember-driven ignition path inside the 5-foot perimeter:

• No combustible vegetation
• Non-combustible ground cover only
• No wood fencing attached to the structure
• Stored combustibles relocated 30+ feet away
• Clean roofs and gutters
• No combustible outdoor furniture in the zone
• Tree branches trimmed 10+ feet from structures
• Dead vegetation removed from the entire property
• Area under decks and stairs cleared
• Container plants limited to fire-resistant species in non-combustible containers
• 1/8-inch metal mesh on attic, foundation, and eave vents
• Non-combustible doormats at all entrances

Each item targets a specific, documented ignition mode. For the technical specification behind each, see The 5-Foot Ember-Resistant Zone: Building Code, Materials, and Compliance.

What didn't change: Zones 1 and 2

AB 3074 added Zone 0 on top of the existing rules. It didn't change Zones 1 and 2:

• Zone 1 (5–30 ft) remains “lean, clean, and green.”
• Zone 2 (30–100 ft) remains “reduce fuel.”

Post-AB 3074, the California defensible space framework is three concentric zones rather than two — Zone 0 is the strictest innermost layer, with Zones 1 and 2 unchanged outside it.

For the full three-zone breakdown, see California Defensible Space Zones: Zone 0, Zone 1, and Zone 2 Explained.

What homeowners need to do

The practical implication of AB 3074 creating Zone 0 is that California homeowners in VHFHSZ areas need to bring their 5-foot perimeter into ember-resistant compliance. Most of that work is straightforward — and most of it most homeowners can do themselves.

Run the free 60-second readiness check to see where your Zone 0 stands today: Start the check →

Sources: AB 3074 (2020) legislative text and findings; California Public Resources Code §4291; Insurance Institute for Business & Home Safety ember testing research; National Institute of Standards and Technology post-fire investigations; CAL FIRE operational guidance.