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Wildfires Can Attack Your House From the Inside — Here's How to Prevent It

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A house undergoes testing in the Insurance Institute for Business & Home Safety's lab.  (Insurance Institute for Business & Home Safety)

Millions of Californians live in fire-prone areas, and many homes were built before modern fire codes.

Buildings don’t have to lie directly in the path of the flames to be at risk. The larger concern comes from something much smaller.

‘During a wildfire, the major source of ignition is the wind-blown ember that lands on or near the house,’ says Steve Quarles of the Insurance Institute for Business and Home Safety.

The wind can carry embers half a mile to a mile ahead of the fire, igniting homes far from the main burn area. But, there are some things homeowners can do to reduce the risk.

1. Create Defensible Space (Need We Say It?)


State fire officials recommend clearing brush and other potential fuels within 100 feet of a home. In fact, it’s required if you live within one of the fire hazard zones designated by Cal Fire or by your city’s codes.

Remove piles of dead leaves and weeds and keep grasses short. Make sure trees are spaced ten feet apart and shrubs are four feet apart. If you live on a slope, those distances should be even larger.

The area within 30 feet of your house should be “lean, clean and green,” according to Cal Fire, with all dead or dry plants removed. Wood piles should also be at least 30 feet from your home.

2. A No-Burn Zone Closest to Home

Homeowners should also consider creating a “noncombustible” zone within 3-5 feet of the house.

“Instead of bark mulch, you’d have rock mulch in that location,” says Quarles.

That also includes the vertical space around your house; make sure tree limbs and shrubs are trimmed back.

Your home’s siding also matters and there are many flame-resistant siding materials on the market. It also shouldn’t touch the ground.

“If your siding reaches all the way to the ground, embers can accumulate at the base of the wall and ignite the siding,” says Quarles.

Quarles recommends exposing 5-6 inches of concrete at the base of the wall or installing metal flashing to protect it, making sure it’s tucked under the siding so water doesn’t accumulate inside it.

3. Check Your Vents

Many homes actually ignite from the inside during a wildfire when powerful winds blow embers into the home through attic, crawlspace or dryer vents.

Fire embers can often enter a home through attic vents. (Insurance Institute for Business & Home Safety)

Houses can have many kinds of vents, but “any vent with wind blowing against it is an inlet,” says Quarles.

Homeowners can minimize that hazard with the right vent covering.

“If it’s a quarter-inch mesh, get an eighth-of-an-inch piece of screening at a minimum (meaning the gaps between wires are no more than one-eighth inch) and attach it at the inlet,” says Quarles. “You can do this from the outside or the inside, whatever is more convenient.”

Finer mesh can get clogged, so it may require more maintenance. Avoid plastic or fiberglass mesh, which can melt. There are also specially-designed vents available for homes in fire-prone areas.

4. Look Up to Your Roof

On your roof, piles of pine needles or gutters clogged with dead leaves will easily ignite from embers.

“It’s just a maintenance thing,” says Quarles. “Homeowners need to keep debris out of the gutter and off of the roof.”

Some roofing materials, like wooden shakes, are especially risky, so experts recommend re-roofing with fire-resistant materials.

If the leaves in your gutter do catch fire, metal drip-edge flashing can also help protect your home.

More resources: check out Cal Fire’s wildfire guide or the University of California’s homeowner’s guide.

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