Ember-resistant vents: close the attic's open door

Embers don't knock. In a wind-driven wildfire, burning debris flies well ahead of the flames, lands on and around houses, and gets in wherever there is an opening. IBHS, which has studied ember entry through vents since 2010, describes the sequence: embers that get into an attic or crawl space can ignite what is stored there, cardboard boxes and old newspapers included, and the building burns from the inside out.

The Bay Area has seen how far embers travel. In October 2017 the Tubbs Fire threw embers a half-mile or more ahead of itself, according to the Press Democrat, and by 2 a.m. it had jumped Highway 101 into Santa Rosa's Coffey Park, a suburban neighborhood on the far side of the freeway from the hills. Attic vents are a direct path for exactly that kind of ember.

Who in the Bay Area should care most

On February 24, 2025, CAL FIRE released its updated Fire Hazard Severity Zone maps for local responsibility areas in the Bay Area and North Coast. Cities had 120 days to adopt them by ordinance. NBC Bay Area reported sharp increases in parts of Sonoma and Napa counties and around San Jose, and mixed changes in Contra Costa County. Some local examples:

• Santa Rosa redrew its wildland-urban interface boundaries in May 2026 to match the state maps, adding about 3,100 properties, mainly in Bennett Valley and Oakmont (Sonoma Index-Tribune).
• Berkeley runs a Home Hardening Mesh Program that gives residents free metal vent mesh and gutter covers. The city's own wildfire page says covering vents with metal mesh is critical.
• San Mateo has designated zones (neighboring Foster City has none). The San Mateo Consolidated Fire Department notes that properties in a zone face wildfire building standards for new construction and renovations, 100 feet of defensible space, and disclosure when sold.

The Berkeley hills along Grizzly Peak Boulevard and Panoramic Hill, where the city adopted its EMBER wildfire rules in 2025, the newly mapped areas around San Jose, and the wildland edges of Sonoma and Napa counties are among the obvious candidates. The Tubbs Fire is the reminder that the edge of the map is not a wall. Check your own address against your city's adopted map.

What the code says, and what changed in 2026

For years, California's wildfire construction rules lived in Chapter 7A of the Building Code and section R337 of the Residential Code. Since July 2021 those rules have required vents in designated areas to be listed wildfire vents tested to ASTM E2886 or listed by the State Fire Marshal (CALBO's summary of the change).

On January 1, 2026, those requirements moved. The Building Standards Commission relocated Chapter 7A and R337 into a new, standalone California Wildland-Urban Interface Code, Title 24 Part 7, adopted from the international WUI code for the first time. The vent rules come with it.

Those standards apply when you build or substantially remodel in a designated area. For an existing house with no project underway, upgrading the vents is voluntary. It is also one of the cheaper ways to harden a house.

Vents show up on the insurance side too: the California Department of Insurance's Safer from Wildfires rules require insurers to offer discounts for listed mitigation work, and ember- and fire-resistant vents are one of the structure measures. Our wildfire insurance discount guide lists the measures; how it applies to your policy is a question for your insurer.

What a good vent retrofit looks like

The guidance from IBHS, Fire Safe Marin, Fire Safe San Mateo and UC ANR lines up on the basics:

• Lose the 1/4-inch screens. They let embers through. Fire Safe San Mateo says not to use 1/4-inch mesh on any vent.
• Metal mesh, 1/8 inch or finer. Noncombustible and corrosion-resistant, with openings between 1/16 and 1/8 inch. Never fiberglass or plastic mesh; it melts and burns.
• Know the trade-off with 1/16 inch. It stops more, but IBHS found it needs more cleaning because debris builds up on the surface.
• Use listed wildfire vents where they count most. IBHS found listed wildfire-resistant vents at the gable end performed better than mesh alone.
• Keep the attic breathing. Finer mesh has less open area (below), and the attic still has to meet the code's ventilation minimum. Sometimes that means an extra vent. See attic ventilation.
• Keep it clean. UC ANR warns that mesh clogged with debris or paint is its own hazard. Check the vents when you clean the gutters.
• Clear the attic. The boxes IBHS mentions are a real fuel source. An attic used for storage is an attic with kindling in it.

Vent by vent

Foundation vents into the crawl space are on UC ANR's list of weak spots too. If your house is on a raised foundation, point them out at the inspection.

Mesh also changes airflow: finer mesh has less open area, and the ventilation math is on attic ventilation. Listed wildfire vents publish their own net free area, and that number is what goes into the math.

Before an evacuation

UC ANR lists one more step for a fire that is actually coming: temporarily covering vents with plywood or metal tape before you leave. It is a stopgap, and the covers have to come off afterwards, because a sealed attic can't vent moisture. It is no substitute for proper vents, but it costs almost nothing to plan for. Keep the pieces cut and labeled in the garage.

Getting it quoted

Vents are one of the easiest jobs to quote from photos. Send a photo of each side of the house, both gable ends, the eaves from below, and a close-up of each kind of vent, plus anything you know about your fire zone. Or book a free in-home inspection, which also covers the attic side of the vents and whether the attic is carrying fuel.

The written quote lists every vent by location and type, what replaces it or what mesh goes behind it, and the attic's resulting net free area. Nothing is due before you sign. While the attic is open, it is a good moment to check for rodent entry points, since gaps an ember can use, a rat can use too.