Mesh versus listed vents

CAL FIRE tells homeowners two things on the same page: cover vents with 1/16–1/8 inch metal mesh, or replace them with State Fire Marshal listed flame- and ember-resistant vents. IBHS Wildfire Prepared Essential uses the same split. Dryer vents are the exception. They need a working flap, not mesh.

You are looking at a vent hole. Hardware-store mesh is a size rule. An 8165 model is a tested assembly. They do not always substitute.

Those are two paths, not two names for one product. See prescriptive path and performance path.

Why it matters

Embers go through holes. A typical older vent has 1/4 inch animal screen, or plastic, or a gap beside the frame. If you buy mesh where the official wants a listed assembly, the drawing fails. If you buy a listed model where mesh was enough, you spent money you did not have to. If you mesh the dryer, lint sits on the screen and becomes fuel. See dryer vents versus mesh.

How it works

An opening is a hole. Mesh answers one question: can an ember this size pass. That is a size rule, not a test method.

ASTM E2886 answers a different question: did this assembly pass a lab test for embers and flame. Some designs use baffles that turn the airflow so embers drop out. Some use intumescent cores that swell when hot. Mesh is often still in the box as a backstop. A pass is a result for that model, in that orientation. It is not a permit.

Fine mesh and listed cores both reduce net free area. Size the vents so the attic still meets ventilation code.

The two paths

Path 1. Prescriptive mesh

You cover the existing opening. The mesh is metal. It does not burn or melt like plastic. Openings are between 1/16 inch and 1/8 inch. That range shows up in CAL FIRE home-hardening guidance, IBHS Essential, and Oregon R327 for many ventilation openings.

What mesh does: it blocks embers larger than the opening.

What mesh does not do: it does not claim an ASTM E2886 flame-intrusion result. It does not fix a gap beside the frame. It does not turn a soffit panel into a listed eave vent.

Hardware-store screen is useful when adopted code accepts this path and you install it tight to the opening. It is the usual low-cost retrofit.

Path 2. Listed assembly

You replace the vent with a model tested to ASTM E2886. In California, many of those models are listed by OSFM in category 8165. Designs differ. Baffles turn the airflow so embers drop out. Intumescent cores swell when hot. Mesh is often still in the box as a backstop.

A listing body names a model number. “Brand X vents” is not a listing. Put the model on the drawing. Deschutes County says it will accept OSFM handbook products when they are shown on the drawings.

Search the BML for the listing ID at the GOVmotus index. That URL is a search box, not a permalink. If the listing program is ICC-ES, open the report PDF. Example handbook rows on this site include BrandGuard soffit and undereave (8165-2232:0500) and Vulcan eave round (8165-2192:0500). Match the model. See how to read a listing.

When the path is not your choice

Oregon R327, where adopted, restricts vents on the underside of eaves, soffits, and cornices. Mesh on an ordinary eave louver may not be enough. R327 points you to a manufactured ember- and flame-resistant vent, or to an opening 12 feet or more above grade. Height is not a skip for the whole house. See the 12-foot rule and eaves.

If your insurer is scoring IBHS Essential, either path can satisfy the vent line. If they require a listed assembly in writing, mesh is not a substitute.

Clark County is a local adopted-code example. Ordinance 5320 keeps the 2024 IWUIC Chapter 5 vent-mesh path unchanged in the reviewed crosswalk. That does not make one-eighth-inch mesh a Nevada statewide rule, and it does not answer the County map, assigned IR class, vent location, or alternative approval. See Clark County IWUIC over Nevada.

Washoe County is a second local Nevada path, but its workflow has more than one input. The accepted 2024 Chapter 5 crosswalk keeps the same one-eighth-inch mesh atom in IR1, IR2, and IR3. The EZ Fire-WUI map supplies parcel hazard; the applicable fire district still supplies water and defensible-space conformity before Table 503.1 yields the class. The map result alone does not make a vent product compliant.

Eagle is a nearby counterexample to assuming Boise’s rule is statewide. Eagle adopts the 2018 IWUIC inside its Ordinance 947 overlay, and its reviewed unchanged model-code path uses mesh no larger than one-quarter inch in IR1 and IR2. Boise locally uses one-eighth inch in IR1. Neither city row tells you that a parcel is in the mapped area or what Table 503.1 outcome the official will assign. Start with the overlay map, then resolve construction.

Jackson Hole Fire/EMS administers another local pair. The Town and County instruments each adopt the 2024 IWUIC, whose reviewed unchanged vent-mesh atom uses no larger than one-eighth inch in IR1, IR2, and IR3. The scopes are not interchangeable: the Town row follows the current corporate boundary, while the County row follows unincorporated land. Fire/EMS still reviews the project and returns Does Not Apply, IR3, IR2, or IR1; the mesh number alone does not answer that review.

Salt Lake City is an edition trap of a different kind. Its current ordinance adopts the Utah book named by state law, which in 2026 is the 2006 UWUI. That book uses one-quarter-inch mesh, not the modern 2024 one-eighth-inch atom. It also treats vent location differently by class: Class 1 and Class 2 keep attic vents out of soffits and eave overhangs, while Class 3 expressly includes soffit vents. The City overlay and assigned class therefore matter before a homeowner copies any mesh number onto a drawing.

Taylorsville adopted the same Utah book as a construction code in Ordinance 25-15 and adopted Exhibit A as its map. That gives the two cities the same edition-specific vent numbers but not the same geography or administration. For Taylorsville, start with the ordinance exhibit and the official class; for Salt Lake City, obtain the Recorder-held City map.

An unvented attic removes attic ventilation openings. Remaining dryer, gable, ridge, and crawlspace openings still need their own path.

Mesh is not a lesser footnote. A listed assembly is not “better” in every code.

What people mix up

• Leaving 1/4 inch animal screen in place.
• Using plastic or fiberglass mesh.
• Treating hardware-store 1/8 inch mesh as an ASTM E2886 vent. Size is not a listing.
• Treating perforated fiber-cement soffit as an ember-rated eave vent. See Findings.
• Buying a listed ridge vent and leaving the gable and crawlspace on 1/4 inch screen.
• Writing a brand name and calling it a listing.
• Treating the GOVmotus URL as a permalink. Search the BML for the ID.
• Covering the dryer with ember mesh.
• Reading “OSFM listed” as an Oregon permit.

How to check

1. Read the adopted code for the lot. If none, you are in voluntary hardening or an insurer checklist.
2. List every vent. Attic, gable, ridge, soffit, foundation, dryer.
3. If the official wants mesh, spec metal, 1/16–1/8 inch, corrosion-resistant, tight install.
4. If the official wants a listed assembly, spec the listing ID and the model. Search the BML for the ID, or open the ICC report if that is the listing program. Put the model on the drawing.
5. Size for airflow after you add mesh or a listed core. Fine mesh reduces net free area.

This site lists example listed vents as records. It does not tell you they are legal on your lot.

Limits

This page does not decide what your building official will stamp. It does not rate airflow for your attic. It does not rank brands. Two 8165 examples are not a shopping catalog. It does not make the house fireproof. FireApproved is not the listing body and not the official.

Related records

• Ember-resistant vents, eaves
• ASTM E2886
• OSFM Building Materials Listing
• IBHS Wildfire Prepared
• How to read a listing
• OSFM listing is usually voluntary
• Show the product on the drawings
• The 12-foot rule
• Dryer vents versus mesh
• Unvented attic
• BrandGuard soffit and undereave (8165-2232:0500)
• Vulcan eave round (8165-2192:0500)
• Vented fiber-cement soffit