California’s newest defensible space requirement — and the zone where most homes are won or lost
Last reviewed: March 2026 · Signed into law: September 2020 · Effective: January 1, 2021
What this law is
Assembly Bill 3074, signed by Governor Gavin Newsom in September 2020 and effective January 1, 2021, added a third defensible space zone to California’s existing framework under Public Resources Code (PRC) 4291. That zone is Zone 0 — the ember-resistant zone covering the 0–5 feet immediately surrounding a structure and any attached deck.
Before AB 3074, California’s defensible space law recognized two zones: Zone 1 (0–30 feet) and Zone 2 (30–100 feet). Research into how homes actually ignite during wildfires had made clear that these zones, while important, left a critical gap — the immediate area around the structure itself, where embers accumulate and find ignition points.
AB 3074 closed that gap by requiring the Board of Forestry and Fire Protection (BOF) to develop regulations governing the ember-resistant zone. Those regulations, adopted under 14 California Code of Regulations (CCR) Section 1299.03, establish the specific requirements for Zone 0. The law also added attached decks to the definition of “structure” for purposes of the ember-resistant zone, recognizing that decks are a primary ember accumulation point.
Zone 0 enforcement has been significantly accelerated. Governor Newsom’s Executive Order N-18-25, issued in January 2025, directed the Board of Forestry and Fire Protection to complete Zone 0 rulemaking no later than December 31, 2025. Property owners should treat Zone 0 as an active requirement and verify current enforcement status with their local CAL FIRE unit or local fire agency.
The fire science behind it
The research that drove AB 3074 is unambiguous. Studies by the Insurance Institute for Business and Home Safety (IBHS), the National Fire Protection Association (NFPA), and post-fire investigations by CAL FIRE and the U.S. Forest Service (USFS) consistently show the same finding: the majority of homes that burn in wildfires are not ignited by direct flame contact. They are ignited by embers.
Embers — also called firebrands — are burning fragments of wood or vegetation that are lofted into the air by a fire and carried by wind. During active wildfire conditions, especially Santa Ana wind events, embers can travel a mile or more ahead of the fire front. They land on and around structures, concentrate in corners, accumulate under decks, collect in gutters, and find their way into vents and gaps. If they find ignitable material — dry vegetation, wood mulch, a wood deck, a pile of leaves — they can start a new fire independently of the main fire front.
This means a structure can ignite even when the fire itself never reaches the property line. It means structures surrounded by otherwise compliant defensible space can still burn if the immediate perimeter contains ignitable material. And it means the first five feet around a structure — Zone 0 — is the single highest-leverage zone for protecting a home.
The physics are straightforward. Embers are small and light. They lose energy quickly. Most come to rest within feet of where they land. The area closest to the structure is where ember density is highest, where accumulation is greatest, and where the consequences of a single ignition are most severe. Eliminating ignitable material in that zone does not require removing trees or clearing an acre — it requires managing a five-foot perimeter with non-combustible materials and keeping it clear of debris.
Standard Zone 1 and Zone 2 management reduces the probability that fire reaches your property. Zone 0 management determines what happens when embers arrive — which, in a Santa Ana wind event, they almost certainly will.
Who this law applies to
AB 3074 applies to all property owners subject to PRC 4291 — anyone who owns, leases, controls, operates, or maintains a building or structure in a State Responsibility Area (SRA) or in a locally designated Very High Fire Hazard Severity Zone (FHSZ) within a Local Responsibility Area (LRA).
The Zone 0 requirement applies to the structure and any attached deck. An attached deck is treated as part of the structure for Zone 0 purposes — the area beneath, around, and on top of an attached deck is subject to the same ember-resistant zone requirements as the structure itself.
Detached structures — sheds, garages, guesthouses — that are separate from the main structure have their own Zone 0 perimeters. Each structure on a property requires its own ember-resistant perimeter.
What it requires
Zone 0 — 0 to 5 feet from the structure and attached deck
Remove all dead plant material, dry leaves, needles, bark, and other organic debris from within 5 feet of the structure and from on top of and underneath any attached deck. This includes debris that accumulates in gutters, on roofs, in valleys, and in corners where walls meet the ground.
No combustible mulch within 5 feet. Use non-combustible ground cover alternatives — decomposed granite, gravel, concrete, pavers, or bare mineral soil. If plants are maintained within Zone 0, they must be low-growing, well-irrigated, and kept free of dead material.
Remove all items stored against the structure that could ignite — firewood, propane tanks, patio furniture with combustible cushions, stored materials. Firewood should be stored at least 30 feet from any structure, or outside Zone 1 entirely.
Screen all vents, eaves, and attic openings with 1/16-inch to 1/8-inch corrosion-resistant metal mesh. Open vents are a primary ember entry point — once an ember enters a structure through a vent, the resulting interior fire is almost always fatal to the building.
For attached decks, the area beneath the deck is treated as Zone 0. Remove all stored items, debris, and combustible material from beneath the deck. If the deck surface itself is wood, the underside and the area beneath are particularly vulnerable to ember accumulation and ignition.
Year-round maintenance
Zone 0 is not a fire season preparation — it is a permanent condition. Leaves accumulate year-round. Debris builds up in gutters in fall and winter. Zone 0 requires regular inspection and maintenance throughout the year, not a single annual clearing.
Official statutory text
The full text of AB 3074 is available at the California Legislative Information website.
- Read the official text
- Read PRC 4291 (as amended to include Zone 0)
- Read 14 CCR Section 1299.03 (Zone 0 regulations):
Enforcement
CAL FIRE’s enforcement of Zone 0 has been significantly accelerated. Governor Newsom’s Executive Order N-18-25, issued in January 2025, directed the Board of Forestry and Fire Protection to complete Zone 0 rulemaking no later than December 31, 2025. That deadline has passed. Property owners in State Responsibility Areas and Very High FHSZ zones should treat Zone 0 as an active enforceable requirement and verify current enforcement status with CAL FIRE or their local fire agency.
This does not mean Zone 0 compliance is optional. Insurance companies are increasingly examining the immediate structure perimeter as part of wildfire risk assessment. A property that fails Zone 0 standards may face non-renewal or higher premiums regardless of formal CAL FIRE enforcement status. Real estate transactions in fire zones are increasingly scrutinized for Zone 0 compliance as well.
Property owners should treat Zone 0 as an active requirement — both because enforcement will come and because the fire science that drives it is not waiting for enforcement to become real.
Addressing the underlying risk
Zone 0 is where the most impactful and most achievable work happens on any fire-risk property. The five feet around your structure does not require heavy equipment, large crews, or multi-day clearing. It requires attention to detail, the right materials, and consistent maintenance.
Start with the deck
If your property has an attached wood deck, that is your highest priority. The underside of a wood deck facing a fire creates a natural ember trap — embers accumulate, heat builds, and ignition follows. Options include enclosing the underside with ignition-resistant materials, using composite or non-combustible decking on the surface, and keeping the area beneath completely clear of stored items, debris, and vegetation. A fire-informed assessment can evaluate your specific deck construction and identify the most cost-effective path to Zone 0 compliance.
Replace combustible mulch
Wood chip and bark mulch within 5 feet of the structure is one of the most common and most easily fixed Zone 0 vulnerabilities. Replacing it with decomposed granite, gravel, or rock costs little and eliminates a significant ignition risk. The visual transition from organic to mineral mulch at the 5-foot line is also a practical guide for ongoing maintenance.
Address vents systematically
Vent screening is a one-time investment with permanent protection value. Eave vents, foundation vents, attic vents, and any other openings in the structure’s envelope should be screened with 1/16-inch mesh. This is a standard home hardening measure that is also addressed under Chapter 7A of the California Building Code for new construction — retrofitting existing structures follows the same logic.
Clear gutters and roof surfaces
Debris in gutters is a direct ignition pathway — embers landing on accumulated leaf litter in a gutter can start a fire that enters the structure through the roofline. Gutters should be cleared before fire season and inspected after any major wind event. Metal gutter guards can reduce accumulation but do not eliminate the need for periodic inspection.
Every Zone 0 vulnerability is a problem that can be solved. A fire-informed property assessment identifies each one specifically, explains the risk it creates, and gives you a prioritized action plan — not a generic checklist, but a property-specific analysis grounded in how fire actually approaches and ignites structures.
Related laws
- PRC 4291 — The foundational defensible space law that AB 3074 amends
- AB 38 — Home hardening disclosure at point of sale
- Civil Code 1102.19 — Defensible space compliance documentation at point of sale
- Chapter 7A — California Building Code requirements for fire-resistant construction
- SB 504 — Insurance mitigation credits that may apply to Zone 0 improvements
Resources and references
- CAL FIRE Defensible Space — fire.ca.gov/dspace — Official Zone 0 guidance and self-assessment
- AB 3074 Official Text — leginfo.legislature.ca.gov — Full bill text as signed
- 14 CCR Section 1299.03 — Board of Forestry Zone 0 regulations
- IBHS Ember-Resistant Zone Research — ibhs.org — Research basis for Zone 0 requirements
- ReadyForWildfire Zone 0 Guide — readyforwildfire.org — CAL FIRE consumer guidance on Zone 0
- NFPA Home Ignition Zone — nfpa.org — Fire science behind structure ignition
Disclaimers
The content on this page is provided for educational purposes only and does not constitute legal advice. Laws and regulations change — always verify current requirements with CAL FIRE or a licensed attorney. Last reviewed March 2026.
Fire science content on this site has been developed with the assistance of AI tools and reviewed for accuracy against current CAL FIRE, NFPA, and peer-reviewed fire behavior research. This content is educational and does not constitute legal or professional advice. For property-specific guidance, consult a qualified wildfire mitigation professional.