Vulnerable vents

By Dwight Good

Editor’s note: This is the fifth installment in a series of articles on wildfire preparation.

Most people believe that wildfires ignite homes through direct contact with flames, but it is rare to have a home ignite this way. Flaming brands and embers can travel a mile or more ahead of the active front of a wildfire and up to 60 percent of wildland/urban interface home ignitions result from embers. Make changes now to reduce the ember threat to your home.  

The Ember Aware campaign is intended to educate people on the risks of ember cast and the actions they can take to reduce those risks, to encourage residents to harden their homes against embers and/or to maintain those ember-resistant features, and to practice ember-safe housekeeping and landscaping. You can learn more at

Tip #5: Vulnerable vent dilemma

Vents play a critical role in your home by allowing excess moisture to escape from the attic and crawl space. If moisture was allowed to accumulate in these areas, your home could be threatened by mold and decay fungi.

During a wildfire, vent openings have also been shown to be one vulnerable spots for ember entry into your home. This creates a dilemma for homeowners. Many vents use wire mesh coverings with a quarter-inch screen. Smaller mesh sizes can become clogged by paint, cobwebs, debris, etc. that reduce air flow. Unfortunately, the quarter-inch mesh is not effective in preventing ember entry into the attic, eave, and crawl space vents. For existing homes, consider the following:

• Replace quarter-inch mesh with one-eighth-inch mesh, if required air flow allows. Be sure to keep the mesh openings unclogged.

• Use metal wire mesh, not plastic or fiberglass.

• Don’t store combustible materials, such as paper, clothing, etc. in the attic or crawl space.

• Clear fallen pine needles, leaves, dried grass and other debris from around vents (a particular problem with through-roof vents, such as a dormer or ridge vent).

• Do not plant shrubs in front of or underneath vent openings.

• Create premade covers out of plywood to install over vent openings if wildfire is approaching and there is time. In an emergency, it may help to fold several layers of aluminum foil and staple over vent openings.

New ember-resistant vent designs are available. Check with your fire marshal or building official for advice on these and other measures to reduce the potential of embers entering your home.  

Fire Marshal Dwight Good, MS, EFO, serves the Morgan Hill Fire Department, South Santa Clara County Fire Protection District and CAL FIRE Santa Clara Unit. He has 24 years of fire service experience. For questions or comments, email [email protected] or call 408.310.4654.