Creating an effective defensible space

Living with fireDefensible Space | Defensible Space FAQ | Wildfire Approaches | Lean, Green, and Clean

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The pre-fire activities implemented by this homeowner included a green and well-maintained landscape, reduction of wildland vegetation around the perimeter of the property, a fire-resistant roof, and a good access road with a turn-around area. As seen in the photo, these pre-fire activities were effective.

…a step-by-step guide (*Please note the recommendations presented in this article are suggestions made by local firefighters experienced in protecting homes from wildfire.  They are not requirements nor do they take precedence over local ordinances.)

STEP ONE:  How big is an effective defensible space

The size of the defensible space area is usually expressed as a distance extending outward from the sides of the house.  This distance varies by the type of wildland vegetation growing near the house and steepness of the terrain.

On the “Recommended Defensible Space Distance” chart presented below, find the vegetation type and percent slope (see“Homeowners Guide to Calculating Percent Slope”) which best describes the area where your house is located.  Then find the recommended defensible space distance for your situation.

For example, if your property is surrounded by wildland grasses and is located on flat land, your defensible space distance would extend out 30 feet from the sides of the house.  If your house sits on a 25percent slope and the adjacent wildland vegetation is dense tall brush, your recommended defensible space distance would be 200 feet.

If the recommended distance goes behind your property boundaries, contact the adjacent property owner and work cooperatively on creating  a defensible space.  The effectiveness of defensible space increases when multiple property owners work together.  The local assessor’s office can provide assistance if the owners of adjacent properties are unknown.  Do not work on someone else’s property without their permission.

Temporarily mark the recommended distance with flagging or strips of cloth tied to shrubs, trees or stakes around your home.  This will be your defensible space area.

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STEP TWO:  Is there any dead vegetation within the recommended defensible space area?

Dead vegetation includes dead trees and shrubs, dead branches lying on the ground or still attached to living plants, dried grass, flowers and weeds, dropped leaves and needles, and firewood stacks.  In most instances, dead vegetation should be removed from the recommended defensible space area.  A description of the types of dead vegetation you’re likely to encounter and the recommended actions are presented below.

STEP THREE:  Is there a continuous dense cover of shrubs or trees present within the recommended defensible space area?

Sometimes wildland plants can occur as an uninterrupted layer of vegetation as opposed to being patchy or widely spaced individual plants.  The more continuous and dense the vegetation, the greater the wildfire threat.  If this situation is present within your recommended defensible space area, you should “break it up” by providing for a separation between plants or small groups of plants.

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STEP FOUR:  Are there ladder fuels present within the recommended defensible space?

Vegetation is often present at varying heights, similar to the rungs of a ladder.  Under these conditions, flames from fuels burning at ground level, such as a thick layer of pine needles, can be carried to shrubs that can ignite still higher fuels like tree branches.  Vegetation that allows a fire to move from lower growing plants to taller ones is referred to as “ladder fuel.”  The ladder fuel problem can be corrected by providing a separation between the vegetation layers.

Within the defensible space area, a vertical separation of three times the height of the lower fuel layer is recommended.

For example, if a shrub growing adjacent to a large pine tree is 3 feet tall, the recommended separation distance would be 9 feet (3 ft. shrub height x 3 – 9 feet).  This could be accomplished by removing the lower tree branches, reducing the height of the shrub, or both.  The shrub could also be removed.

STEP FIVE: Is there an area at least 30 feet wide surrounding your house that is “Lean, Clean, and Green?”

The area immediately adjacent to your house is particularly important in terms of an effective defensible space.  It is also the area that is usually landscaped.  Within an area extending at least 30 feet from the house, the vegetation should be kept:

  • Lean – small amounts of flammable vegetation;
  • Clean – no accumulation of dead vegetation or other flammable debris; and
  • Green – plants are health and green during the fire season.

The “Lean, Clean, and Green Zone Checklist” will help you evaluate the area immediately adjacent to your house.

STEP THREE:  Is there a continuous dense cover of shrubs or trees present within the recommended defensible space area?

Sometimes wildland plants can occur as an uninterrupted layer of vegetation as opposed to being patchy or widely spaced individual plants.  The more continuous and dense the vegetation, the greater the wildfire threat.  If this situation is present within your recommended defensible space area, you should “break it up” by providing for a separation between plants or small groups of plants.

STEP SIX:  Is the vegetation within the recommended defensible space area maintained on a regular basis?

Keeping your defensible space effective is a continual process.  At least annually review these defensible space steps and take action accordingly.  An effective defensible space can be quickly diminished through neglect.

This technique involves the elimination of entire plants, particularly trees and shrubs, from the site.  Examples of removal would be the cutting down of a dead tree, or the cutting out of a flammable shrub.

The removal of plant parts, such as branches or leaves,constitutes reduction.  Examples of reduction are pruning dead wood from a shrub, removing low tree branches, and mowing dried grass.

Replacement is the substitution of less flammable plants for more hazardous vegetation.  For example, removal of a dense stand of flammable shrubs and planting an irrigated, well maintained flower bed would be a type of replacement.

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Reduction

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HOW DO I CHANGE THE VEGETATION ON MY PROPERTY TO REDUCE THE WILDFIRE THREAT?

The objective of defensible space is to reduce the wildfire threat to a home by changing the characteristics of the adjacent vegetation.

Defensible space practices:

  1. Increase the moisture content of vegetation.

  2. Decrease the amount of flammable vegetation.

  3. Shorten plant height.

  4. Alter the arrangement of plants.

This is accomplished through the “Three R’s of Defensible Space.”  The article “Creating an Effective Defensible Space” provides detailed information about changing vegetation characteristics for defensible space.

CREATING AN EFFECTIVE DEFENSIBLE SPACE*

. . . A Step-by-Step Guide

*Please note the recommendations presented in this article are suggestions made by local firefighters experienced in protecting homes from wildfire.  They are not requirements nor do they take precedence over local ordinances.