Zone 0 Windows California: AB 3074 Ember-Resistant Rule

Zone 0 windows in California are the windows that fall within the 0-to-5-foot horizontal ember-resistant zone immediately surrounding a home in a High or Very High Fire Hazard Severity Zone. The zone itself was established by Assembly Bill 3074, signed into law in September 2020, which directed the State Fire Marshal and CAL FIRE to develop regulations defining the ember-resistant zone for new construction and existing homes. As of May 2026, the final OSFM regulations remain in the rulemaking process — but the Public Resources Code §4291 statutory framework is already in effect, and Chapter 7A of the California Building Code already requires ember-resistant glazing for any window in a WUI Fire Hazard Severity Zone, regardless of where Zone 0 ultimately lands.

For a Colfax homeowner, that overlap is the practical answer. Whether or not the final Zone 0 rule lands at five feet, three feet, or some performance-based alternative, every window within the building envelope of a home in Placer County's High or Very High FHSZ already has to meet §707A.3 ember-resistant glazing standards under the 2026 California Building Code. Zone 0 adds a separate layer — the noncombustible ground plane, removal of attached combustible items, and ember-resistance for everything within five feet of the wall — that sits on top of the window-product requirement.

I'm John, owner of Colfax Glass. I've been installing windows in Colfax, Auburn, Foresthill, and the I-80 Sierra Foothill corridor for 25-plus years and have watched this rule develop in real time since the 2018 Camp Fire. This guide walks through what Zone 0 actually requires for windows in 2026, where the OSFM rulemaking stands, how Zone 0 overlaps with Chapter 7A, and the specific steps a Colfax homeowner should take now — both for compliance and for measurable wildfire risk reduction.

Zone 0 is the innermost defensible space zone established by Public Resources Code §4291, expanded by AB 3074 in 2020 to require ember-resistance from zero to five feet measured horizontally outward from every exterior wall of a structure. The zone is the highest-priority area for ignition prevention because it is where wind-driven embers most often deposit, ignite combustible material, and transfer flame to the building envelope. CAL FIRE's post-fire incident investigations from the 2017 Tubbs Fire, 2018 Camp Fire, 2020 LNU Lightning Complex, and 2024 Park Fire consistently identify the 0-to-5-foot zone as the highest-probability ignition pathway for structures that survived initial radiant heat exposure (CAL FIRE, 2024).

The statute applies to homes in State Responsibility Area parcels classified as High or Very High Fire Hazard Severity Zone. For Placer County, that captures the Colfax I-80 corridor, most of Auburn east of Highway 49, all of Foresthill and Iowa Hill, and substantial portions of Meadow Vista and Weimar. The 2024 OSFM Fire Hazard Severity Zone maps for SRAs and the 2025 Placer County Local Responsibility Area FHSZ adoption are both available through the Placer County FHSZ viewer and the CAL FIRE statewide FHSZ map.

For windows specifically, Zone 0 matters in two ways. First, the zone itself must be ember-resistant — no combustible vegetation, no wood mulch, no attached wood fences, no firewood stacks, no patio furniture made of combustible materials within five feet of the wall. Second, anything within Zone 0 that has the potential to ignite — including the window itself, the surrounding trim, and the cladding immediately around the opening — needs to either be noncombustible or pass an ember-intrusion test. That is where the statute connects directly to glazing product selection and to Chapter 7A's existing window requirements.

AB 3074 was signed by Governor Newsom on September 29, 2020. The statute amended Public Resources Code §4291 to add the ember-resistant zone requirement and directed the Office of the State Fire Marshal to develop implementing regulations. The original statutory deadline was January 1, 2023, but the rulemaking process has been substantially extended through multiple public comment periods, CEQA review, and revisions responding to industry, agency, and homeowner stakeholder input.

As of the most recent OSFM update in early 2026, the final regulatory text has not yet been published in the California Code of Regulations. The most recent draft language released for public comment kept the 0-to-5-foot horizontal measurement, defined what "ember-resistant" means for ground cover and attached structures, and addressed the phased application to existing versus new construction. The phasing is the central political question — applying the rule retroactively to all existing structures in the affected zones would affect hundreds of thousands of California homes.

The practical consequence for 2026 Colfax homeowners is that Zone 0 is statutorily required but not yet enforced through fire inspector citations under a finalized OSFM regulation. Local fire departments and CAL FIRE units may still conduct PRC §4291 inspections under existing pre-2020 standards, which include the 100-foot defensible space requirement (now subdivided into Zone 1 from 0-30 feet and Zone 2 from 30-100 feet under prior Cal Fire guidance). Defensible space compliance is verified during structure-protection inspections, before insurance renewal in some cases, and during real estate transactions in High and Very High FHSZ areas under PRC §4291.5.

Watch the OSFM rulemaking docket directly for the final publication date. Once published, the regulation will set a compliance deadline — likely 12 to 24 months for new construction and a longer phased deadline for existing structures, based on the most recent draft language. Colfax homeowners doing a permitted window replacement project in 2026 should design the project as if Zone 0 will be enforced for new and substantially-altered exterior work, because the building permit can fold the requirement into the inspection process even before the OSFM rule lands.

Not directly — at least not yet. Zone 0 as written in PRC §4291 and the latest OSFM draft regulations focuses on the ground plane, attached combustible items, and the immediate exterior environment within five feet of the wall. The statute does not include a freestanding requirement that every existing window in Zone 0 be replaced with a new ember-resistant unit. The window-product requirement is in Chapter 7A of the California Building Code, which is triggered by new construction, additions, and major remodels — not by Zone 0 enforcement on its own.

That distinction is important because Zone 0 enforcement, when finalized, will likely begin with the things a homeowner can change quickly and inexpensively: removing wood mulch, clearing combustible vegetation within five feet of the wall, relocating firewood stacks, replacing wooden gates that attach to the structure with metal, and similar high-leverage low-cost actions. Replacing every single-pane window within five feet of grade will not be a Zone 0 enforcement action; it will be a Chapter 7A enforcement action triggered when the homeowner pulls a building permit for the work.

Where it does become a window decision is voluntary upgrade and insurance pressure. The California FAIR Plan and the admitted carrier market both reference home-hardening checklists derived from Chapter 7A, IBHS Wildfire Prepared Home, and Cal Fire's Ready For Wildfire program. Multi-pane ember-resistant windows are a checked item on every one of those programs. A Colfax homeowner with single-pane windows facing a Zone 0 vegetation hazard is subject to two compounding pressures: the Cal Fire defensible space inspection that flags the vegetation, and the insurance carrier inspection that flags the windows. Neither is technically Zone 0 enforcement, but both push the same direction.

The practical sequencing I recommend for Colfax homeowners is: address Zone 0 ground-plane items first because they are inexpensive and have no permit overhead, then address window upgrades as part of a planned Chapter 7A WUI window project when budget allows. The two work together — the cleared Zone 0 reduces the ember and flame exposure to the window, and the ember-resistant glazing handles whatever exposure does occur.

California Building Code Chapter 7A §707A.3 is the existing window-product standard for any new window installed in a Wildland-Urban Interface Fire Hazard Severity Zone. It requires that every exterior window or glazed opening either (a) be constructed of multi-pane glazing with a minimum of one tempered pane, (b) be tested and approved as a complete window assembly per SFM Standard 12-7A-2, or (c) be glass block. The tempered-pane requirement is the most common compliance path, and it applies to the entire window — fixed lights, operable lights, picture windows, transoms, and skylights all count.

For a Colfax home in a High or Very High FHSZ, this standard is in effect today regardless of Zone 0. Any building permit pulled for a window replacement, addition, or major remodel will be inspected against §707A.3. The Placer County Building Department flags non-compliance at the rough inspection and at final, and a noncompliant unit will not pass — meaning the window has to be replaced before certificate of occupancy or final approval. That is not a Zone 0 question; it is a Chapter 7A question that has been the rule since 2008.

The relationship between §707A.3 and Zone 0 becomes important once the OSFM rule is finalized. The most recent draft language requires that any combustible material within Zone 0 — which includes window frames if they are vinyl or wood and any combustible trim around the opening — meet ember-intrusion performance criteria. SFM 12-7A-2 is the tested standard for the complete window assembly, and a window certified to that standard provides documented evidence that the assembly resists ember intrusion at the head, jamb, sill, and glass-to-frame interface. For new construction, that is the cleanest path. For existing homes, an SFM 12-7A-2 retrofit is feasible but typically requires full-frame replacement rather than insert-style retrofit, because the nailing flange and the surrounding flashing are part of the tested assembly.

For a complete walk-through of the §707A.3 product options and the SFM 12-7A-2 testing protocol, see our dedicated fire-resistant windows for WUI zones guide. For the broader assembly-level detailing including the wall around the window, the Chapter 7A wall assembly guide covers §707A.4 and the window-to-siding interface.

The technical basis for ember-resistant glazing rests on three reference documents that any Colfax homeowner getting deep on this should know about: ASTM E2588, NIST Technical Note 1925, and the IBHS roof and window component studies. ASTM E2588 is the standard test method for ember intrusion through building envelope penetrations, including window assemblies. The test exposes a sample assembly to a controlled ember stream and measures whether ignition occurs on the interior side over a defined exposure period. SFM 12-7A-2 incorporates ASTM E2588 protocols for the window-assembly test.

NIST Technical Note 1925, published in 2017, documented experimental ember-flux measurements during simulated wildfire exposures. The study quantified ember deposition rates at building surfaces under varying wind speeds and vegetation densities, providing the empirical foundation for the 0-to-5-foot Zone 0 distance specifically. Embers concentrate in the leeward zone immediately adjacent to vertical walls, and the 0-to-5-foot distance captures more than 80 percent of the ember-deposition mass under the test conditions (NIST, 2017). That is why AB 3074 picked five feet rather than three or ten — the empirical data supported five feet as the high-leverage distance.

The IBHS Wildfire Prepared Home component studies extended this work specifically to glazing. IBHS testing identified single-pane glass as a primary failure mode under both ember and radiant exposure, with failure typically occurring within 90 to 180 seconds of sustained radiant heat at flame-front intensity. Tempered dual-pane glass extended survival times to over 10 minutes under the same exposure conditions, with the inner pane intact even after the outer pane failed thermally. That extended survival window is what allows ember-resistant glazing to actually deliver wildfire protection in real fire-front passage scenarios — the building envelope holds long enough for the front to pass, after which interior ignitions become unlikely.

The practical takeaway for Colfax homeowners: the test data supports the rule. Single-pane windows are the highest-leverage upgrade target in the Zone 0 envelope. Tempered dual-pane glass is the mainstream solution. SFM 12-7A-2 tested assemblies are the premium solution for new construction or substantial remodels. The choice between them depends on budget, project scope, and how aggressive the homeowner wants to be on insurance and resale positioning.

The cleanest 2026 sequencing for a Colfax homeowner in a High or Very High FHSZ is to address Zone 0 ground-plane items first, then window upgrades on a planned timeline that aligns with budget and natural replacement cycles. Ground-plane items are inexpensive, do not require permits, deliver immediate ember-deposition risk reduction, and demonstrate hardening intent to insurance carriers. Window upgrades are larger investments with permit overhead, but they pair with the cleared Zone 0 to deliver the actual fire-front survival capability.

Start with the items inside five feet of the wall. Remove all wood mulch, bark chips, pine needles, and combustible vegetation from the 0-to-5-foot horizontal band around the entire structure. Replace with decomposed granite, gravel, river rock, concrete, or stone. Remove or relocate firewood stacks to at least 30 feet from the structure. Replace any wooden fence or gate that attaches directly to the home with metal; if the fence cannot be replaced, install a noncombustible swing gate or break section in the first five feet from the wall. Move propane tanks to at least ten feet from the structure if they are within Zone 0. Remove combustible patio furniture, doormats, and stored items from within five feet of the wall during fire season.

Next, evaluate the windows specifically within Zone 0 — typically all ground-floor windows and any second-floor windows on grade-level walls (split-level or hillside homes). Identify which are single-pane, which are aging double-pane with potential seal failure, and which are tempered dual-pane in good condition. Single-pane windows are the priority replacement target. Failed-seal double-pane windows are second priority because they signal the broader window system is approaching end of life and the glass-only IGU swap option often makes more sense than full-frame replacement when the frames are still sound.

For any planned permitted window work, design to Chapter 7A §707A.3 from the start. Specify tempered dual-pane glass minimum, ENERGY STAR Most Efficient if possible to also hit the Title 24 prescriptive path, and SFM 12-7A-2 tested assemblies if the budget supports the premium. Document the install with NFRC labels, contractor invoices, and permit final inspection sign-offs — these become the documentation package for FAIR Plan and admitted-carrier hardening discounts and for any future Zone 0 enforcement once the OSFM rule is finalized. The California Wildfire Mitigation Program grants may cover all or part of the cost for income-qualified homeowners in active project areas.

Zone 0 compliance is a meaningful insurance lever in 2026, even before the OSFM rule is final. The California FAIR Plan and the admitted-carrier market both reward documented home-hardening using checklists that overlap heavily with Zone 0 and Chapter 7A requirements. The Safer from Wildfires regulation, adopted by the California Department of Insurance in 2022, requires admitted carriers to offer rate reductions for combinations of hardening measures, with discounts of up to 16.4 percent on the FAIR Plan and varying amounts in the admitted market (CDI, 2025).

Multi-pane ember-resistant windows are on the Safer from Wildfires checklist, as are the Zone 0 ground-plane items: noncombustible ground cover within five feet, no combustible storage in Zone 0, defensible space compliance, ember-resistant vents, and Class A roofing. Stacking these earns the larger end of the discount. A Colfax homeowner with $4,500 to $5,500 annual premium can typically save $500 to $900 per year by documenting the full hardening package, which compounds quickly against the project cost.

The California Wildfire Mitigation Program (CWMP), funded through FEMA and Cal OES and administered locally through county OES departments, continues to fund full home-hardening retrofits at no cost for income-qualified homeowners in active project areas. The program prioritizes High and Very High FHSZ parcels and explicitly includes window replacement, vent retrofits, deck upgrades, and Zone 0 ground-plane work. As of spring 2026, Placer County has active CWMP project areas, and we have helped Colfax and Foresthill customers complete the application process. For the detailed program walk-through, see our California wildfire home hardening grants for windows post.

The overall economic stack for a Colfax Zone 0 + Chapter 7A window project in 2026 looks like this: project cost (varies with scope), minus any CWMP grant funding (potentially full project cost for qualifying homes), minus the recurring annual insurance discount (typically $400 to $900 per year for a fully-hardened home), plus the long-term durability premium of tempered dual-pane glass over single-pane in the Sierra Foothill freeze-thaw cycle. The federal Section 25C tax credit ended December 31, 2025 under the One Big Beautiful Bill Act and is no longer part of the math — see our federal tax credit windows 2026 post for the full breakdown of what changed.

Several Zone 0 myths circulate in Colfax homeowner forums, real estate disclosures, and contractor sales pitches that are worth correcting before they drive bad decisions. The first is that Zone 0 already requires window replacement on existing homes — it does not, at least not under current published regulation. The window-product requirement comes from Chapter 7A and is triggered by permits, not by Zone 0 enforcement.

The second is that the 0-to-5-foot zone is measured from the property line. It is not. Zone 0 is measured horizontally from every exterior wall of the structure, outward five feet. A home set 30 feet from the road has Zone 0 wrapping around the entire building footprint, not extending from the road.

The third is that vinyl windows automatically fail Zone 0. The current OSFM draft language addresses combustible materials within Zone 0 broadly but does not categorically prohibit vinyl windows that meet §707A.3. The most likely final outcome is that windows tested per SFM 12-7A-2 satisfy Zone 0 regardless of frame material, while non-tested vinyl windows may face additional scrutiny under the final ember-resistance criteria. Until the rule is final, vinyl tempered-dual-pane windows that meet §707A.3 remain code-compliant for Chapter 7A and are a reasonable path for budget-constrained projects.

The fourth is that Zone 0 only applies to brand-new homes. The statute does not exempt existing structures — it directs OSFM to develop regulations addressing both new and existing — and the most recent draft includes phased compliance for existing homes. The final phasing schedule is pending, but the political signal from the 2024 and 2025 fire seasons is that the existing-home phase will not be skipped.

The fifth is that Zone 0 replaces or supersedes Chapter 7A. It does not. They are complementary regulations. Chapter 7A is in the California Building Code and governs what gets installed during permitted construction. Zone 0 is in the Public Resources Code and governs the immediate environment around the structure regardless of permit activity. Both apply concurrently to homes in High and Very High FHSZ.

The single best 2026 move for a Colfax homeowner in a High or Very High FHSZ is to act on Zone 0 ground-plane items now and plan window upgrades to Chapter 7A on a budget-aligned timeline. Ground-plane items deliver immediate ember-deposition risk reduction at low cost, demonstrate hardening intent to insurance carriers, and pre-comply with the most likely final OSFM rule regardless of what the precise distance and material specifications turn out to be. Window upgrades are a larger investment but pair with the cleared Zone 0 to deliver the actual structure-protection capability — and they are increasingly required by insurance carriers regardless of statutory enforcement.

Do not wait for the final OSFM rule before clearing Zone 0. The vegetation, mulch, and combustible-storage items within five feet of the wall are the highest-leverage actions on every IBHS, Cal Fire, FAIR Plan, and admitted-carrier checklist already published. Even if the final rule lands at three feet rather than five, the work done at five feet is fully credit-eligible. If the final rule lands at five feet — the most likely outcome based on current draft language and the NIST TN 1925 empirical data — the work is exactly compliant.

For windows, pace the project to your natural replacement cycle and budget. If you have failed-seal double-pane windows or single-pane windows in Zone 0, prioritize those for a planned 2026 or 2027 replacement to Chapter 7A §707A.3 with SFM 12-7A-2 tested assemblies where the budget supports the premium. If your existing windows are tempered dual-pane in good condition, you are already most of the way to compliance — focus on the surrounding wall assembly, flashing, and the ground-plane items rather than tearing out functional glazing.

Track the OSFM rulemaking docket and the Placer County Building Department updates. Subscribe to the OSFM email list at osfm.fire.ca.gov for rulemaking notifications. The final rule will set a specific compliance deadline, and the deadline determines whether 2026 voluntary upgrades become 2027 or 2028 mandatory compliance work. Acting voluntarily now lets you choose the timing, the contractor, and the product mix. Waiting until the deadline narrows all three.

For a complete Zone 0 and Chapter 7A assessment on a Colfax, Auburn, Foresthill, Iowa Hill, or other Placer County foothill home, contact Colfax Glass for a free site review. We walk through the FHSZ classification, the Zone 0 ground-plane items, the window product options, the FAIR Plan documentation requirements, and the CWMP eligibility check in a single visit, and the inspection itself is no-charge regardless of whether the project moves forward.