Home and Community Safety & Health Safety

Fences and mulch beds can become ‘bridges’ for wildfires, researchers say

Fences and mulch are common contributors to the spread of fires in wildland-urban interface communities. This photo depicts flames that spread from a burning fence to a building about 6 feet away during the 2018 Camp Fire. Photo: CALFIRE

Although fences and mulch can add to your home’s curb appeal, they also can put your home at greater risk of wildfire damage, researchers are warning homeowners.

National Institute of Standards and Technology scientists wanted to look at how fires – particularly wildfires – can spread to a home or other structure via various combustible fencing materials and styles and/or types of mulches. They carried out a total of 187 experiments under five different scenarios: mulch only, fence only, fence and mulch, parallel fences, and long-range firebrand experiments. A propane burner was used to ignite the materials up to 6 feet downwind.

One key finding: The fire spread faster when mulch was near fencing, which acted as “bridges” for flames.

“In the highest hazard category, the fences and mulch are going to carry the fire along toward your house in a matter of a few minutes, not hours,” NIST physicist Kathryn Butler, co-author of a report detailing the study results, said in a press release.


The fires also moved faster when the fencing was placed side by side, as in multiple fences separating two properties. In that scenario, the flames took as little as four minutes to engulf an 8-by-6-foot fence. By comparison, a flame on a single set of fence panels took an hour to move about 3½ feet.

The researchers recommend replacing combustible landscaping with noncombustible materials such as cement, stone or steel whenever possible. Additionally, avoid doubling up on fences, because those that were even 3 feet apart led to larger, faster-moving flames.

Further, homeowners shouldn’t place combustible fencing where it may interfere with exit routes, and should look into “hardening” their homes, especially where the risk of wildfires exists. That process can involve upgrading, adding or replacing (with less flammable materials) up to 40 different components around the house, including decks, windows and gutters.

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