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United States / Build / Fire-resistant vents

Fire-resistant vents

Program and model No adopted WUI code we can source here. IBHS Wildfire Prepared asks for the inspection measures, and the 2024 IWUIC model says the same floor.

National floor. A ZIP opens the same question at a place where a sourced instrument exists.

Fire-resistant vents take two paths. Prescriptive: noncombustible, corrosion-resistant metal mesh with openings of 1/16 to 1/8 inch, per CAL FIRE guidance and IBHS Wildfire Prepared, 1/8 inch under Colorado's CWRC. Performance: a vent assembly tested to ASTM E2886 for ember and flame intrusion and listed in California's OSFM category 8165 by model. Mesh is not a listed vent and a perforated soffit is neither. Where Oregon R327 is adopted, eave and soffit vents are restricted to manufactured ember- and flame-resistant vents or openings 12 feet or more above grade.

What the sourced rules ask for

For national vents, the national vents requirement is 2018 IWUIC Class 1–2 vent mesh. On national vents, it is shown as model code. Read the national vents rule, then compare 12 matched national vents products.

Review 18 national vents place answers before choosing among national vents records. The national vents links keep the rule, products, and place differences together.

Find what applies near you

Enter a ZIP before browsing the complete evidence. Matching, inherited, and place-neutral records will move first; other places and unmapped application rows will fold into expandable groups. Nothing is removed. All 3 state rule sections remain available.

The rule

Model code “noncombustible corrosion-resistant mesh with openings not to exceed 1/4 inch (6.4 mm)”

2018 IWUIC Class 1–2 vent mesh. The unamended 2018 IWUIC specifies noncombustible corrosion-resistant mesh with openings no larger than one-quarter inch for Class 1 and Class 2 vents.

Products matching the model-code floor

Model code Product matches below are limited to vents and trace to the named requirement.

Additional products matching the voluntary program

Voluntary program Product matches below are limited to vents and trace to the named requirement.

How sourced instruments differ

Three paths, not three names for one product. A listed 8165 assembly is an ASTM E2886 record. Mesh is a size rule. A dryer flap is a lint path. Oregon R327, California CWUIC, Colorado CWRC, and IBHS do not always pick the same path. CWRC 403.4 is attic, rafter, and underfloor, not a dryer-vent rule.

Oregon R327 where adopted

Listed assembly
R327.3.2 allows vents designed to resist burning embers and flame. Underside of eaves still needs the official’s accepted manufactured vent or a 12-foot opening.
Metal mesh
R327.3.2 names 1/16–1/8 inch mesh for attic, soffit, rafter, and underfloor openings. It is not a substitute for the eave-underside rule.

California CWUIC

Listed assembly
Specifiers often pull an OSFM 8165 model. Listing is still voluntary for most WUI products.
Metal mesh
Prescriptive mesh cover appears in CAL FIRE home-hardening. CWUIC-mapped jobs often use the listed-assembly path. Confirm the project scope.

Colorado CWRC

Listed assembly
CWRC 403.4.1 is one Class 1 path: listed vents tested to ASTM E2886. Class 2 includes that rule. Confirm the local ordinance.
Metal mesh
CWRC 403.4.2 is the other Class 1 path: noncombustible corrosion-resistant mesh with openings not more than 1/8 inch for enclosed attics, rafter spaces, and underfloor. It does not name 1/16 inch. Confirm the local ordinance.

Questions

What is an ember-resistant vent?

A vent assembly that resists ember entry and direct flame, shown by an ASTM E2886 test and, in California, an OSFM 8165 listing by model. Fine metal mesh is the prescriptive alternative, not the same product.

What kind of vent mesh is recommended to prevent ember intrusion?

Noncombustible, corrosion-resistant metal mesh with openings from 1/16 to 1/8 inch, per CAL FIRE guidance and the IBHS standard; Colorado's CWRC sets 1/8 inch. Quarter-inch mesh keeps animals out and lets embers through.

Are soffit vents fire rated?

Vents are listed or meshed, not fire-rated. A perforated soffit panel is cladding (OSFM 8160 is the underside covering); an ember-resistant soffit vent is an 8165 listed assembly or, where Oregon R327 applies, one of its two eave exceptions.

Is 1/8 inch mesh enough?

CAL FIRE and IBHS treat noncombustible, corrosion-resistant mesh between 1/16 and 1/8 inch as a prescriptive ember path. That is not the same as an ASTM E2886 listed vent. The adopted code and the building official decide which path is required on your job.

Why not 1/4 inch mesh?

Quarter-inch mesh is common on older homes because it keeps animals out. Embers can still pass. CAL FIRE tells you to replace it or cover it with finer metal mesh.

Do I need an OSFM listed vent in Oregon?

Oregon R327, where a city or county has adopted it, allows mesh or vents designed to resist ember and flame. Deschutes County says it will accept products from the OSFM WUI handbook when those products are shown on the drawings. That is local practice. Confirm with the building official.

Can I vent the eaves?

Where R327 is adopted, eave, soffit, and cornice vents are restricted. The usual exceptions are a manufactured ember- and flame-resistant vent, or an opening 12 feet or more above grade. Other attic and crawlspace openings still need mesh or a listed vent.

Is a perforated fiber-cement soffit a vent?

No. It is cladding. It is not 1/8 inch mesh and it is not an ASTM E2886 assembly. See Findings.

Where this answer differs

6 sourced rows

  • Model code 2018 IWUIC Class 1–2 vent mesh — The unamended 2018 IWUIC specifies noncombustible corrosion-resistant mesh with openings no larger than one-quarter inch for Class 1 and Class 2 vents.
  • Model code 2021 IWUIC Class 1–2 vent mesh — The unamended 2021 IWUIC specifies noncombustible corrosion-resistant mesh with openings no larger than one-quarter inch for Class 1 and Class 2 vents.
  • Model code IWUIC vent mesh — The unamended 2024 IWUIC model code specifies noncombustible corrosion-resistant vent mesh with openings no larger than one-eighth inch as a prescriptive path.
  • Voluntary program IBHS Base forced-air vent closure — The current IBHS Base standard calls for a functional louver or flap on forced-air vents such as dryer and central-vacuum exhausts.
  • Voluntary program IBHS Base vent mesh — The 2025 IBHS Base standard permits a prescriptive vent-covering path using documented noncombustible, corrosion-resistant mesh with openings no larger than one-eighth inch.
  • Voluntary program IBHS Plus metal forced-air vent closure — The current IBHS Plus standard adds noncombustible construction to the Base functional-closure requirement for forced-air vents.