American River Watershed Institute arwi.us
Fire Safety Project | Remedies

Defensible Space

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Introduction

The risk of structural damage by fire can be reduced by providing a "defensible space." Such a space consists of an area surrounding a structure where the vegetation has been modified to mitigate the fire hazard and provide an opportunity for firefighters to safely defend a structure in the path of an approaching wildfire.

Defensible space does not require the area to be free of vegetation. Plants are often desirable to protect soils from erosion and provide an aesthetic and ecological balance to the environment.

Vegetation that does not easily ignite should be planted in the defensible space. Trees and shrubs are acceptable as long as they are widely spaced and do not provide a continuous path for a fire to climb from the ground to a tree crown or roof (as a fuel ladder). Proper landscape maintenance can dramatically improve the fire safety of a yard.

Since January 2005, California has required 100 feet of defensible space around every home in rural areas. This means clearing excess vegetation and opening areas to prevent a fire from quickly spreading and engulfing many homes in its path. We saw this in October 2003 when San Diego, Riverside, and Ventura counties were consumed in a fire storm and suffered huge losses of life and property.

California law — Public Resources Code 4291 (PRC 4291) — mandates 100 foot defensible space perimeter around residences. The California Department of Forestry & Fire Protection (CDF) explains Homeowners Responsibility under the law.

Definitions

Concentric circles around your house define the home ignition, defensible space, and wildland reduction zones.
Reducing fire risk with
defensible space
(Click image to see larger view)
  • Defensible Space (PRC 4291): Area surrounding a structure where fire protection or firebreak is made by removing all brush, flammable vegetation, or combustible growth which is located up to 30 feet (up to 100 feet in heavy fuel areas) from such structure or to the property line, whichever is nearer. The goal is to create an area where ground based fire suppression resources, such as fire engines, can successfully defend the structure from an advancing fire.

  • Defensible Landscape: The area outside of the defensible space zone where additional fuel reduction is completed to enhance the protection value of the defensible space zone around a structure. Increased aesthetics and habitat values are planned for in this prescription.

    • Individual homeowners are responsible for maintaining defensible space around their homes.
    • State law now requires 100 feet of defensible space clearance in most rural areas of California.
    • Maintain low plantings near house and water in summer to keep plants green.
    • Trim lower limbs of trees, especially those near house.

Defensible Space Guidelines

Prepare around your home

  • Plants in and around your home should be well maintained, free of debris and "fire-safe." Remove all dry grass, leaves, brush and dead wood from property. Create islands of vegetation (a "fuel mosaic") so that fire does not have a path to your house.

  • No trees should have branches within 6 feet of your roof-cut the branches or remove the tree if necessary. Trees and shrubs should be spaced at least 10 feet apart and limb up 6-10 feet.

  • Clear fire hazards 30-100 feet around buildings. The area within 6 feet of your house is especially hazardous-do not store firewood and other combustibles within this zone, especially under decks. Stack firewood 30-100 feet from all buildings and clear 10 feet around the pile.

  • Clear 10 feet around propane tanks and keep barbecue propane tanks as far away from the house as possible.

  • Metallic screens provide protection to windows from radiant energy from fires and some protection against wind-blown debris.

  • Defensible space must be maintained every few years to keep new vegetation growth from creating another fire hazard.

Post your address

  • Large reflective numbers clearly visible at your driveway entrance and on your house.

Inspect and correct roof problems

  • Keep roof and rain gutters clear of leaves, needles, and dead branches.
  • Cover stovepipes and chimneys with 1/2 inch screen and remove all overhanging limbs.
  • Replace wood shingle roofs with fire resistant materials.
  • Box in eaves.
  • Cover attic vents with 1/8 - 1/4 inch metal screen.

Under Decks and Buildings

  • Enclose with solid siding or 1/8 inch metal screen to keep out a blizzard of embers.

Plantings

  • In a high-intensity fire, everything will burn. However, proper landscaping and plant selection can render some landscaping safer than others, and at least lessen the risk to any adjacent structures or reduce the spread of a fire.

  • Plant plants that are Fire Safe; replace plants that are Fire Hazards. Some common examples include:

    Fire Hazard Fire Safe
    Juniper ground cover Vinca
    Rosemary Rock Rose
    Pine trees Oregon Ash Tree
    Eucalyptus Trees Mulberry Trees
    Cyprus Trees Valley Oak Trees
    Juniper Windbreaks Redbud Shrubs and Trees
    See also:

FireWise Plants

You can reduce the fuel load for a potential fire by landscaping with fire-resistant plants. Fire resistance can be enhanced by plant selection, placement, and maintenance. (See list of FireWise plants.)

FireWise Landscaping Tips

  • Create a defensible space perimeter by thinning trees and brush within 30 feet around your home.
  • Beyond 30 feet, remove dead wood, debris and low tree branches.
  • Eliminate small trees and plants growing under trees. They allow ground fires to jump into tree crowns.
  • Space trees 30 feet apart and prune to a height of 8 to 10 feet.
  • Place shrubs at least 20 feet from any structures and prune regularly.
  • Plant the most drought-tolerant vegetation within three feet of your home and adjacent to structures to prevent ignition.
  • Provide at least a 10 to 15 foot separation between islands of shrubs and plant groups to effectively break-up continuity of vegetation.
  • Landscape your property with fire-resistant plants and vegetation to prevent fire from spreading quickly.

Use Fire Resistant Plants

  • Check your local nursery or county extension service for advice on fire resistant plants that are suited for your environment.
  • Create fire-safe zones with stone walls, patios, swimming pools, decks and roadways.
  • Use rock, mulch, flower beds and gardens as ground cover for bare spaces and as effective firebreaks.
  • There are no "fire-proof" plants. Select high moisture plants that grow close to the ground and have a low sap or resin content.
  • Choose plant species that resist ignition, like rockrose, iceplant or aloe.
  • Fire-resistant shrubs include hedging roses, bush honeysuckles, currant, cotoneaster, sumac and shrub apples.
  • Plant hardwood, maple, poplar and cherry trees that are less flammable than pine, fir and other conifers.
    See also:

Summary

Defensible space must be maintained every few years to keep new vegetation growth from creating another fire hazard.
  • 100' Defensible Space Update — In January 2005 a new state law became effective that extended the defensible space clearance around buildings and structures from 30 feet to 100 feet. Proper clearance out to 100 feet dramatically increases the chance of your house surviving a wildfire. This defensible space also provides for firefighter safety when protecting homes during a firestorm.
"[CDF] encourages the public to extend hazardous fuel reduction beyond the PRC mandated defensible zone into the adjacent 'Defensible Landscape' zone. This is the area outside the defensible space zone where a property owner can reduce fuels to a lesser degree than the defensible space zone but effectively add to the protection of the property."
CDF Unit Fire Plan