Vents

Vents are direct openings into your attic and crawl space. During a wildfire, wind pushes embers through them, and a home ignited this way burns from the inside out. Ember-resistant vents are among the cheapest, highest-value hardening upgrades a homeowner can make.

An ember that enters an attic or crawl space ignites what it finds there: stored boxes, newspapers, insulation, dust. By the time smoke is visible outside, the fire is established inside the structure. Ember-resistant venting is addressed in Chapter 7A of the California Building Code for new construction, and commercial WUI vents are widely available for retrofits.

What to Do

• Cover all vent openings with 1/16-inch to 1/8-inch corrosion-resistant metal mesh, or replace them with listed ember- and flame-resistant vents.
• Replace common 1/4-inch screens. They do not stop embers.
• Never use fiberglass or plastic mesh. It melts and burns.
• Protect vents in eaves and cornices with baffles backed by 1/16-inch mesh. Mesh alone is not enough in these locations.
• Keep windblown debris cleared from all vent inlets, especially ridge vents with plastic components.

What the Research Shows

IBHS tested vent types against wind-blown ember exposure (Quarles, Vulnerability of Vents to Wind-Blown Embers, IBHS 2017). The findings:

1. For under-eave inlet vents, soffited-eave construction limits ember entry better than vents in open-eave rafter blocking, and is the preferred construction type.
2. 1/4-inch mesh should not be used on any vent. Use 1/8-inch or 1/16-inch, and expect the finer mesh to need more frequent cleaning.
3. Wildfire-resistant vents in gable ends outperformed backing mesh alone.
4. Gable end vents are large and vertically oriented, which makes them ember catchers. Avoid them where possible; where you cannot, use a wildfire-resistant gable vent that has passed the ASTM E2886 test.
5. Avoid non-wildfire-resistant ridge and off-ridge vents. Options that performed well: Miami-Dade wind-driven-rain-compliant ridge vents, wildfire-resistant off-ridge vents, and turbine vents.