When investigators walk a burned neighborhood, the houses that were lost with no flame contact — no burning tree, no neighbor’s house — usually failed one way: embers blew into the attic or the crawl space through a vent, smoldered in the insulation, and the house burned from the inside out an hour after the fire front passed. A quarter-inch louvered vent is a front door for an ember. Eighth-inch metal mesh closes it.
What to buy
- Metal mesh, 1/8-inch openings (the state’s Safer from Wildfires standard is 1/16 to 1/8 inch). Galvanized or stainless hardware cloth from any hardware store, sold by the roll. Not fiberglass window screen, which melts, and not 1/4-inch, which lets embers through.
- Stainless or galvanized staples or self-tapping screws with washers, depending on whether the vent frame is wood or metal.
- Tin snips, gloves, a caulk gun and a tube of exterior-grade caulk for the edges.
For a typical valley house: one 24-inch by 10-foot roll, a box of staples, one tube of caulk. Around $40–80.
Finding every vent
Walk the house twice — once at ground level, once looking up. Count them; most homes have more than the owner thinks.
- Foundation / crawl-space vents at ground level along the base of the wall. The most exposed, because embers collect against the house.
- Eave and soffit vents under the roof overhang — long strips or round plugs.
- Gable vents — the triangular or rectangular louvers high on the end walls.
- Roof vents and turbines, and the attic fan.
- Dryer and bathroom exhaust vents — these need a damper, not mesh; check the flap closes.
- Garage vents, often forgotten. The garage is where the gas cans are.
Doing it
- Cut the mesh an inch larger than the vent opening on all sides.
- Fit it on the outside of the vent, over the existing louver or screen, so embers hit metal before they reach anything.
- Fasten every 2–3 inches around the edge. A gap at one corner is the whole job wasted.
- Run a bead of caulk along the edges so nothing can lift it and so the mesh doesn’t rattle in a Santa Ana.
- For high gable vents and roof vents, this is a ladder job — two people, or a roofer’s afternoon.
Mesh reduces airflow slightly. On a house with a well-ventilated attic that is fine; if the attic was already marginal, a listed ember-resistant vent (below) keeps the airflow.
When to use listed vents instead
Manufactured ember-resistant vents — the ones with a WUI listing from the State Fire Marshal — use baffles or intumescent strips that seal shut in heat, and they are the right answer for new construction, remodels, and any vent you are replacing anyway. They cost more per vent ($30–100) but need no mesh and satisfy the building code outright. For an existing house on a budget, mesh first, listed vents when you replace.
While you are up there
Clear the gutters and sweep the roof valleys (task 2). Check that the spark arrester on the chimney is intact. Look at the gap where the roof edge meets the fascia — bird-stop tiles and eave blocking are the other common ember entry.
Then log it
Vent screening is Resident Structural Work on the activity form, and it is one of the nine property-level items your insurer has to credit. Take a dated photo of the finished vents before you put the ladder away.
References: IBHS Wildfire Prepared Home; California Department of Insurance, Safer from Wildfires. This is general guidance; a free Fire Safe Council assessment will tell you which vents on your house matter most.