Landscaping with Wildfire Exposure in Mind can Protect Homes

Creating a defensible space around a home avoids pathways that could allow wildfire to burn directly to the home.

Aug 15, 2021 – Posted by Pamela Kan-Rice – What can Californians do to improve the chances of their homes surviving a wildfire? According to consultants at UC Cooperative Extension, simple measures around the home can greatly improve the chances of a home surviving wildfire.

In wildfires, buildings are not only threatened by the burning front of the fire, but also by burning embers, which are piled up in front of the fire front and land on fuels such as vegetation or mulch next to the house and ignite new fires. Traditional defensive space tactics are designed to mitigate threats from the blazing front of the fire, but do little to address vulnerabilities from embers on or next to a structure.

“Without considering the embers-related risks, reasonable space efforts address only part of the forest fire hazard – particularly wind-powered fires where embers are the main source of fire spread,” said co-author Yana Valachovic, UC Cooperative Extension Forest consultant in Humboldt and Del Norte counties.

Concrete sidewalk and driveway line the house.

Zone Zero, the area within 1.5 m of the house, should be cleared of flammable plants, planters, mulches, and wood that could ignite from embers. Photo by Yana Valachovic

An updated publication from the University of California Agriculture and Natural Resources describes how embers, radiant heat, and direct flame contact ignite buildings and shares cost-effective measures local residents can take to effectively create defensible space.

“The new release is up to date with changes in California’s Defense Space Policy and addresses Zone Zero, or the missing ingredient in Defense Space,” said Valachovic. “The publication also offers a thoughtful discussion of plant lists and their limitations.”

The likelihood of a home surviving a forest fire can be greatly improved by careful attention to three things: careful design and maintenance of the landscaping; Awareness and handling of combustible materials on the property such as leaf litter, piles of wood and patio furniture; and installation of fire and embers resistant building materials with appropriate installation and maintenance.

“You don’t have to spend a lot to protect your home from these forest fires,” said Valachovic.

Zone Zero, the area within five feet of the house, is the most vulnerable area around the house, according to researchers at the UC Cooperative Extension. “In wind-driven fires, the embers are the main source of fire spread,” said Valachovic.

They recommend removing flammable plants, planters, mulches, and piles of wood within the 1.5 m perimeter of the home and below attached decks.

To prevent a wooden fence from introducing fire into the house, consider replacing the five feet closest to the house with a non-combustible section, such as a concrete block wall, metal gate, or wire fence.  Photo by Yana Valachovic

To prevent a wooden fence from introducing fire into the house, consider replacing the five feet closest to the house with a non-combustible section, such as a concrete block wall, metal gate, or wire fence. Photo by Yana Valachovic

“While it can be a radical change, clearing the area next to the house will reduce the risk of direct flame contact from the embers and radiant heat that are responsible for many home losses,” she said. “Since embers can collect at the foot of an external wall, it is also important to create a 15 centimeter long, non-flammable zone between the floor and the beginning of the external wall of the building.”

Colorful illustrations in the publication demonstrate the three-zone strategy of defensible space and how placing trees on a sloping landscape can prevent fire from climbing from tree to tree to reach a house at the top of the slope.

The 12-page “Reducing the Vulnerability of Building to Wildfire: Vegetation and Landscaping Guidance” can be downloaded free of charge from https://anrcatalog.ucanr.edu/pdf/8695.pdf.

Place plants, shrubs and trees so that they do not cause a fire in the house or in the treetops.

Place plants, shrubs and trees so that they do not cause a fire in the house or in the treetops.

“Landscaping for fire is part of an overall strategy aimed at reducing the risk to the home,” said co-author Steven Swain, UC Cooperative Extension environmental horticultural advisor for Marin and Sonoma counties. “To reduce the risk of losing your home, start at home and train from there,” he recommended.

Swain, Valachovic and Stephen Quarles, advisor emeritus for UC Cooperative Extension, are currently updating a paper on retrofitting homes for forest fire resistance.

Steps on how to harden houses against forest fires can also be found on the Fire in California website: https://ucanr.edu/sites/fire/Prepare/Building.
Source: UC ANR

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