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Window Film and Wildfire: What California’s WUI Glazing Rules Actually Say
If your home is in a Fire Hazard Severity Zone, you may have heard that window film helps against wildfire. California’s code, the state fire agencies and the research we read focus on the glass and the frame. Here is what they say, and where film does and does not fit.
Published October 21, 2026 · Armored Glass Solutions
The Short Answer
Short answer: film is not a wildfire product. The glass is what code and research focus on
California’s wildfire building code lists four ways a window can comply, and film is not one of them. None of the code, State Fire Marshal, CAL FIRE, Board of Forestry or Department of Insurance documents we read mentions film as a wildfire measure. They focus on multi-pane tempered glass, rated glazing, glass block, screens, shutters and clearing what can burn near windows. We install film, so we are telling you that up front.
Film can still do its normal jobs on these homes, such as cutting solar heat and UV. We do not suggest it adds any wildfire protection.
The Code
What California’s WUI glazing rule actually says
For the 2025 code cycle, California moved its wildfire construction rules into the California Wildland-Urban Interface Code (Title 24, Part 7); the International Code Council lists its effective date as January 1, 2026. Many guides still use the older names, Building Code Chapter 7A and Residential Code R337. The 2025 Residential Code now points from R337 to Part 7.
Section 504.8 covers exterior windows, window walls, glazed doors, windows within exterior doors, and skylights. It says they “shall be constructed of any of the following”:
- “Multilayered glazed panels with at least one pane of tempered glass complying with Section 2406 of the California Building Code.”
- “Glass block.”
- “Glazing with a fire-protection rating of not less than 20 minutes when tested according to NFPA 257 or UL 9, and shall be exempt from the hose stream test.”
- “Glazing meeting the performance requirements of SFM Standard 12-7A-2.”
Film is not on the list. UC ANR’s Fire Network notes that the tempered pane “can be either the inner or outer pane,” and that options 3 and 4 are performance tests using “a radiant heat flux or a flame impingement exposure.” Section 2406 is the same safety-glazing family we cover in is window film safety glass?
The chapter applies to buildings “hereafter constructed, modified or relocated into or within wildland-urban interface areas,” and its note ties it to Fire Hazard Severity Zones and WUI areas. One exception is “Additions to and remodels of buildings originally constructed prior to July 1, 2008.” We did not find a section on replacing windows in an existing home, so ask your city or county building department whether a replacement has to meet 504.8.
How Windows Fail
How windows fail in a wildfire
CAL FIRE’s Wildfire Home Retrofit Guide says “The most vulnerable part of a window is the glass.” Thermal stress from flames or radiant heat starts cracks at the outer edge that run inward. If the glass falls out, or the frame ignites or deforms, embers or flames can get in. Our reading: it is the same kind of edge stress we describe in window film on dual-pane glass, at far higher heat.
After the January 2025 Palisades and Eaton fires, UC Cooperative Extension advisor Yana Valachovic wrote that “The windows were the weak link,” with radiant heat from nearby burning buildings or landscaping breaking panes or deforming vinyl windows. She wrote that where she saw dual-paned, tempered glass windows and noncombustible siding, homes survived. That is one expert’s field observation, not a survival rate.
How much heat glass takes depends on the glass and the test. CAL FIRE says tempered glass is “three to four times more resistant to heat exposures than typical annealed glass.” A 2023 IBHS research summary puts typical annealed double-pane windows at about 25 kW/m² (kilowatts per square meter), citing Quarles and Gorham (2020), and tempered panes at about 40 kW/m², citing Babrauskas (2003). It reports that in IBHS tests a tempered outer pane of a double-paned window failed after about 10 minutes of heat from a burning shed 30 feet away. A 2025 peer-reviewed lab study of small 23 cm windows found that survival of tempered glass at a radiant heat flux “as low as 30 kW/m² is not consistent.” These are different tests, so there is no single breaking point.
Embers are the other threat. CAL FIRE says they can ignite homes up to a mile away and recommends screens on operable windows.
Guidance
What the agencies and researchers recommend
- CAL FIRE: dual-paned windows with at least one tempered layer, screens on operable windows, and deployable noncombustible shutters if neighbors or outbuildings are within 30 feet. Its low-cost list says: “When it’s time to replace your windows, replace them with multi-paned windows that have at least one pane of tempered glass.”
- Board of Forestry, Zone 0 (0 to 5 feet from the house): adopted by the Board in August 2026 and, when we checked, still in final state review with no effective date published. The draft rule bars vegetation “within two (2) feet of windows.” The guidance highly recommends tempered glass on windows facing a neighboring structure within 30 feet. Zone 0 is a defensible-space rule, not a glazing rule.
- IBHS Wildfire Prepared Home (voluntary, December 2025): its Plus level calls for “Multipaned glass with at least two tempered panes,” 20-minute rated glass, or glass block. IBHS’s 2023 research summary says “it is necessary to have both panes tempered.”
Code minimum: one tempered pane in multi-pane glass. Voluntary standard: two. Insurance lists: multipane windows or shutters, no tempering. Different bars, and none includes film.
Where Film Fits
Where film fits, and where it does not
The 2022 edition of the State Fire Marshal’s WUI Products Handbook that we read lists complete window assemblies, frame and glass, and no film. We could not check the current listing.
Section 503.2.5 says: “Use of paints, coatings, stains or other surface treatments are not an approved method of protection as required in this chapter.” It sits in the section on ignition-resistant materials, not the glazing section, and does not name film. We read it as the code’s general stance that an applied surface layer is not itself a way to meet the chapter. How it applies to anything on glass is for your building official.
The only primary-source statement we found tying film to wildfire is from a 2010 UC ANR publication: “Research conducted in Australia has shown that a reflective film on the exterior surface of the outside glass provides effective protection against radiant exposures (Bowditch et al. 2006).” That is reflective film on the outside of the glass, from one 2006 report we could not retrieve, and the later CAL FIRE, IBHS and code documents we read do not adopt it. NFRC notes film is often applied to the room-side glass surface, so our reading is that the finding does not describe a typical interior install. The same publication says laminated glass “did not perform any better than annealed glass” in that research, and we found no source on how security film behaves in a wildfire.
A 2025 study in Fire Technology found double-pane windows passed 13% to 43% of the incoming heat, against 39% to 60% for single pane, and a low-emissivity coating cut that to 5% to 14%. Those were factory coatings on the pane facing the heater, not window film. We found no test of retrofit film under wildfire-type heat.
A note on words: in our ceramic solar film post, “radiant heat” means the sun’s infrared. In wildfire research it means heat from burning buildings and vegetation; the 2025 study tested 10 to 50 kW/m². A film’s solar heat-rejection figure is not a wildfire rating.
Spec Sheets
“Class A” on a film spec sheet is not a fire rating for your window
Some film data sheets list an ASTM E84 class; 3M’s Scotchshield Ultra S800 sheet lists “Flammability (ASTM E84) Class A.” ASTM describes E84 as “a 10-min fire-test response method” that measures flame spread along a surface, compared with red oak and fiber-cement board. ASTM also says the test “does not by itself incorporate all factors required for fire-hazard or fire-risk assessment” under actual fire conditions. In 3M’s E84 bulletin, Class A means a flame spread index of 0 to 25 and smoke developed of 0 to 450.
Our reading: E84 asks how far flame spreads along a surface; the WUI glazing paths ask whether a window resists radiant heat or flame. None of the 3M film sheets we read mentions wildfire. Our post on decorative film on office glass makes the same point: it is a surface-burning test for the film, not a fire rating for glass.
Insurance
Insurance: what the discount lists actually name
The California Department of Insurance’s Safer from Wildfires page lists “Upgraded windows” and says: “Multi-paned glass or added shutters all qualify.” The regulation behind the program, 10 CCR § 2644.9 (operative October 14, 2022), requires insurers that use wildfire risk rating to reflect “Multipane windows, including dual pane windows, or functional shutters, which when closed, cover the entire window and do not have openings.”
Neither names film or requires tempered glass, so an insurance credit and the building code are different standards. We did not research discount amounts; ask your insurer.
Your Home
If your home is in a Fire Hazard Severity Zone: what to check
- The tempered label: UC ANR says to “look for a small label in a corner of the window.” Our safety glass post explains the permanent mark.
- Pane count and glass type: single-pane or all-annealed glass is a replacement question, not a film question. See window film or new windows.
- Neighbors within 30 feet: tempered glass on windows that face them, per Board of Forestry guidance, and possibly noncombustible shutters, per CAL FIRE.
- Screens: on operable windows, to catch embers.
- Vegetation: within two feet of windows, which the draft Zone 0 rule addresses.
- Before you evacuate: close windows and skylights, and, as UL FSRI advises, move curtains and furniture away from windows.
- Replacements: ask your building department what a new window has to meet.
Everyday Jobs
What film can still do on these homes
Film can still cut solar heat (see ceramic solar film), reduce UV, and add a layer for everyday impact safety within the limits in is window film safety glass? None of that is a wildfire benefit, and we will not sell it as one.
Questions
Window film and wildfire: FAQ.
Does window film make my windows wildfire-compliant in California?
No code path we found includes film. Section 504.8 of the 2025 California Wildland-Urban Interface Code accepts multi-layered glazed panels with at least one tempered pane, glass block, glazing with a 20-minute fire-protection rating under NFPA 257 or UL 9, or glazing that meets SFM Standard 12-7A-2. None of the code, State Fire Marshal, CAL FIRE, Board of Forestry or Department of Insurance documents we read mentions film. Compliance is about the glass and the frame.
Will window film help my windows survive radiant heat from a wildfire?
That has not been established. The one primary-source mention we found is a 2010 UC ANR publication citing a single Australian study of reflective film on the exterior surface of the glass. A 2025 lab study found that factory low-E coatings on the heated side cut heat transfer, but it did not test window film. We found no test of retrofit film, interior or exterior, under wildfire-type heat. The agencies point to multi-pane tempered glass, screens, shutters and clearing vegetation near windows.
My film's spec sheet says Class A. Is that a fire rating for my window?
No. Class A refers to ASTM E84, a 10-minute test of how far flame spreads along a material's surface, compared with red oak and fiber-cement board. ASTM says the test does not by itself assess fire hazard or fire risk under actual fire conditions. It is a surface-burning class for the film, not a fire rating for your window and not a wildfire rating.
How do I know if my windows already meet the WUI glazing rule?
Start by looking for a small label in a corner of the window, as UC ANR suggests, to see whether a pane is tempered. Multi-pane glass with at least one tempered pane is one of the four code paths, and the tempered pane can be the inner or the outer one. Single-pane or all-annealed glass points to a replacement question, not a film question. Whether replacing a window on your home has to meet the rule is a question for your city or county building department.
Do upgraded windows get an insurance discount in California?
The Department of Insurance's Safer from Wildfires program lists multi-paned windows or added shutters, and the regulation behind it, 10 CCR 2644.9, requires insurers that use wildfire risk rating to reflect multipane windows or functional shutters. Window film is not on either list. Neither list requires tempered glass, so an insurance credit does not mean a window meets the building code. We did not research discount amounts; ask your insurer.
Sources
Where these findings came from.
We read these on October 20, 2026 (the NFRC page on October 17). Code text is quoted from the 2025 California editions. Older documents are labelled; two were read from Internet Archive copies because the original links no longer load. Where we give our own reading or inference, we say so. This post is general information, not a code determination; your building department decides what applies to your home.
- International Code Council, 2025 California Wildland-Urban Interface Code, Title 24, Part 7, with January 2026 errata. Adopted code. Link; Chapter 5: Link.
- International Code Council, 2025 California Residential Code, Chapter 3 (R337 note). Adopted code. Link.
- UC ANR Fire Network, Windows. University extension; undated. Link.
- CAL FIRE / Office of the State Fire Marshal, WUI Products Handbook, June 7, 2022 edition, county-hosted copy. State agency; dated. Link.
- CAL FIRE Ready for Wildfire, Hardening Your Home. State agency; undated. Link.
- CAL FIRE, UNR Extension and UC Cooperative Extension, Wildfire Home Retrofit Guide (SP-20-11), January 2021. Link.
- CAL FIRE, Low-Cost Retrofit List. State agency; undated. Link.
- IBHS (Hedayati, Quarles, Hawks), Wildland Fire Embers and Flames: Home Mitigations That Matter, April 2023. Insurance-funded research institute. Link.
- IBHS, Wildfire Prepared Home Technical Standard, December 2025. Voluntary designation program, not code. Link.
- Quarles, Valachovic et al., Home Survival in Wildfire-Prone Areas: Building Materials and Design Considerations, UC ANR Publication 8393, May 2010. University; dated; Internet Archive copy. Link.
- Valachovic, UC ANR fire expert highlights materials, components and actions that saved homes from LA fires, UC ANR Green Blog, March 4, 2025. Field observations. Link.
- Schrader et al., Experimental Study of Heat Transfer Through Windows Exposed to a Radiant Panel Heater, Fire Technology 61 (2025). Peer-reviewed. Link.
- UL FSRI, research update on window heat transfer, February 14, 2025. Research institute. Link.
- California State Board of Forestry and Fire Protection, Defensible Space Zones 0, 1 and 2; Zone 0 guidance, September 2026; draft regulation summary, August 2026. State board. Link; guidance; draft rule.
- ASTM International, E84-25 standard summary page. Standards body. Link.
- 3M, ASTM E84 Surface Burning Characteristics of Building Materials, technical bulletin, November 2014. Maker; dated. Link.
- 3M, Scotchshield Safety & Security Window Film Ultra S800 Technical Data Sheet, Rev. G, January 2025. Maker. Link.
- NFRC consumer guide, Window Film (efficientwindows.org). Rating organization; undated. Link.
- California Department of Insurance, Safer from Wildfires. State agency; undated. Link.
- California Code of Regulations, Title 10, § 2644.9, via the Office of Administrative Law’s official site. Regulation. Link.
Keep Reading
Related reading.
Is window film safety glass?
What safety glazing standards cover, how tempered and laminated glass differ, and where film fits.
Read the guide →Window film or new windows?
When film is enough, when replacement is the right call, and how to tell which one your glass needs.
Read the guide →Window film on dual-pane glass: what thermal stress actually is
The mechanism behind dual-pane thermal breakage, and how to check for it before film goes on.
Read the guide →Home in a fire hazard zone?
Tell us what windows you have and what you want them to do. We will look at the glass and tell you plainly whether it is a glass question or a film question. If it is a glass question, we will say so, and we will only go over film options for the jobs film actually does.