Most homes lost in a wildfire are never touched by the flame front. They are ignited by embers — burning fragments carried on the wind, sometimes a mile or more ahead of the fire itself. Those embers land on the roof, drift under the eaves, and get pulled into the attic through the one opening every house is required to have: a vent.
A vent is a hole in your house that has to stay a hole. You cannot seal it, because the attic and the crawlspace need to breathe. What you can do is cover it with something an ember cannot get through and a fire cannot destroy.
The Number That Matters: 1/16″ to 1/8″
California specifies a range, not a single size. Mesh openings must be at least 1/16″ and no more than 1/8″.
Both ends of that range are doing work.
Too coarse and embers get through. The 1/4″ hardware cloth that has been stapled over crawlspace vents for decades stops rodents perfectly well and stops embers not at all. An ember small enough to pass a 1/4″ opening is still more than large enough to start a fire in dry insulation.
Too fine and the vent stops working. This is the mistake people make when they assume finer is safer. Window screen mesh clogs with dust, lint, and paint, and once it clogs the attic loses the ventilation it was designed around. You trade a fire risk for a moisture and heat problem, and a blocked vent can fail an inspection just as fast as an unprotected one.
What Changed on January 1, 2026
If you are reading older guidance — and most of what is online still is — it points you to Chapter 7A of the California Building Code. That chapter no longer holds these requirements.
In the 2025 Title 24 code cycle, the Building Standards Commission removed Chapter 7A and moved its provisions into a new standalone code: the California Wildland-Urban Interface Code (CWUIC), Title 24 Part 7, effective January 1, 2026. It consolidates what used to be spread across CBC Chapter 7A, CRC Section R337, and Fire Code Chapter 49. Chapter 7A is now essentially a pointer to the new code.
There is a second change that matters more than the renumbering. Under CWUIC Section 504.10.1, primary attic and foundation vents in a WUI area are expected to be vents listed by the California State Fire Marshal or tested to ASTM E2886 — a tested assembly, not a screen you add yourself. The 1/16″ to 1/8″ mesh specification appears in Section 504.10.2, covering off-ridge and ridge vents.
So be clear about which situation you are in:
- Building new, or replacing a vent, in a WUI zone. You most likely need a listed, tested vent. Mesh alone will not satisfy your inspector.
- Hardening an existing home. Screening your vents with compliant metal mesh is the standard retrofit measure, and it is what fire safe councils and CAL FIRE guidance have long recommended. It is a real, meaningful improvement over 1/4″ cloth or bare openings.
We sell the mesh. We do not certify vents, and no mesh we sell is a listed vent assembly. Confirm your specific requirement with your local building department or fire authority before you buy. Requirements vary by jurisdiction and by how close you are to a mapped hazard zone.
Material: Noncombustible And Corrosion Resistant
The code asks for two properties, and they are separate.
Noncombustible rules out the obvious. Fiberglass and plastic insect screen melt well below the temperature of an ember shower. A vinyl screen does not slow embers down; it disappears and leaves an open hole. Metal only.
Corrosion resistant is the requirement people underestimate, because it is about time rather than heat. A vent screen has to still be there in fifteen years. Screen mesh sits in an eave or against a foundation where it gets condensation, salt air near the coast, and no maintenance at all. Plain steel rusts through and leaves a hole exactly where you did not want one.
Stainless is the material to use if you are doing this once and want to forget about it. Type 304 handles most of California; 316 is worth the money near salt water. Galvanized is the budget option and is genuinely noncombustible, but the zinc is a sacrificial coating with a finite life — and if it is galvanized before weaving or welding rather than after, the cut ends and joints are bare steel from day one. That distinction matters here.
Where It Goes
- Attic and gable vents. The highest-value target. Embers riding a convection current end up here.
- Eave and soffit vents. Hardest to reach, and the most commonly skipped. Heat and embers collect under an overhang.
- Foundation and crawlspace vents. Usually the oldest screen on the house, and usually 1/4″.
- Dryer and utility vents. Screen these carefully — a dryer vent that clogs is its own fire hazard, so these need to stay serviceable.
- Chimneys. Spark arrestors are governed by a separate requirement with a different opening size. Do not assume vent mesh is the right answer there.
What We Stock
We have been cutting wire cloth in Hayward since 1938, and we cut to size, so you are not buying a hundred-foot roll to screen six vents.
- 8 Mesh Galvanized Hardware Cloth, 27 gauge — roughly a 0.108″ opening, comfortably inside the range. Galvanized after weaving. The economical choice for a whole-house retrofit.
- 1/8″ Mesh 304 Stainless Crimped Woven, .063″ wire — heavy stainless at the top of the range. Stiff enough to hold its own shape across an opening and effectively permanent.
- 1/16″ Perforated Aluminum — noncombustible, corrosion resistant, and rigid. A cleaner look than woven mesh where the vent is visible from the street.
Not sure which fits your opening, or need it cut to a specific size? Send us the dimensions or call (510) 887-8787. Tell us what you are screening and we will tell you what we would use.
This article is general information about wire mesh, not a code compliance determination. Wildfire construction requirements vary by jurisdiction and change over time. Verify your requirements with your local building department or fire authority.