Creating Defensible Space Zones

Defensible Space Zones

Defensible Space Zones

What is defensible space?

A barrier to keep wildfire from getting too close to your property.

Focus on the following three areas:

Zone 1: The area adjacent to your home or business
(0-5 ft)

The objective in this area is to prevent flames from making direct contact with structures.

  • In high risk areas such as chaparral, this extra attention needs to be extended throughout a full 30-feet.

  • Pay particular attention to the types of vegetation and mulch you select for this area.

  • Whatever types of plant materials are chosen for this area, they must be carefully maintained.

  • Reduce the chances of a ground fire in this area by selecting products such as noncombustible mulches, including rock, gravel, and noncombustible hardscape features such as brick and concrete walkways and surfacing that will reduce your wildfire exposure.

  • Choosing low-growing, irrigated herbaceous plant materials is another good option.

 Zone 2: The area within 30 feet or to the property line

  • Use this area as a buffer zone where you work very hard to reduce the intensity of the wildfire. This includes reducing the amount of radiant heat that could impact your home or business and the local generation of embers.

  • This area requires the most thinning and horizontal separation of trees and other vegetation, and removal of items that could cause a very intense fire close to your business.

  • The objective of the thinning and separation is to reduce the chances that vegetation will provide a direct path for the wildfire flame front to approach your business.

  • Items that also should be removed from this 30-ft zone include wood structures, boats, trailers and anything else containing combustible materials that could produce an intense fire close to your business.

Steps to improve defensible space in Zones 1 and 2

  • Do trees or branches hang over the building? Prune them back so that they are a minimum of 10 feet away.

  • Do you have vegetation that is close to, adjacent to or under vents, soffits or windows?

    • Remove flammable vegetation and replace with fire resistant varieties.

    • Plants in the area within 5 feet of the building can expose combustible siding, windows or interior corners to an increased risk of damage from embers and flames.

    • All vegetation needs to be maintained, but ground cover or small plants will be less of a problem here.

    • Larger plants, particularly those that tend to generate an abundance of dead material will pose a significant threat.

    • For all plants, shorten the height, remove branches that are close to the ground, prune to reduce the amount of material in the plant, and remove dead material. 

  • Do you  have plants with the following characteristics? If so, replace them.

    • Generate ground litter from bark, leaves, or seeds that slough off

    • Have (very low moisture content) dead material within the plant

    • Have small branches and needles that can easily ignite

    • Have a high resin or volatile content 

  • Has vegetative debris accumulated in the areas that connect the deck and walls, under the deck or at the base of exterior walls or fencing? 

    • Inspect for and clear all vegetative debris on a regular basis.

    • Remove dead vegetation close to the building, paying attention to material on and underneath plants. 

  • Do you use mulch?

    • Mulch can help keep the ground moist and reduce the need for watering, but it also can become a fire hazard.

    • Avoid using wood, bark and rubber mulch products, particularly small pieces of bark or those with hairy components such as “gorilla hair” mulch.

    • Consider rock mulch or other noncombustible materials. 

  • Are trees pruned to eliminate ladder fuels?

    • Ladder fuels are those that will allow fire to climb up the bark and into the upper portion of the tree

    • Prune trees to eliminate ladder fuels. 

  • Do you have any fences, firewood, trellises or other yard features that could bring flames too close?

    • Combustible structures should be moved 30 feet to 50 feet away from the building.

    • Separate groups of non-tree vegetation to make it more difficult for fire to move horizontally.

Zone 3: The area beyond 30 feet 

Use this area extending at least 100-feet from your building or to the property line as a buffer zone to reduce the intensity of the approaching wildfire and to change a crown fire into a ground fire.

Steps to improve your defensible space in Zone 3

  • Do you have dead plant material and tree branches in the area between 30 feet and 100 feet from your home or business or up to the property line? 
    Remove dead plant materials and tree branches. 

  • Are trees closely packed together with branches overlapping? 
    Thin out trees to reduce the chances that fire can spread from one tree crown to the next. 

  • Are trees in this area pruned to eliminate ladder fuels? 
    Ladder fuels are those that will allow fire to climb up the bark and into the upper portion of the tree. Prune trees to eliminate ladder fuels. 

How Topography Influences Wildfire Risk

The topography around your home or business, which includes the slope of the land and the direction the structure faces, is a major consideration in assessing the risk exposure to wildfire. Wildfires burn up a slope faster and more intensely than along flat ground and a steeper slope will result in a faster moving fire, with longer flame lengths.

Steps to determine the steepness of the slope:

  1. Select a mark on the slope and walk 10 paces downhill;

  2. If your head is below the mark you have a steep slope.

Protecting mid-slope or steep slope properties

If your structure is set back less than 15 feet for a single-story and 30 feet for a two-story building take additional precautions:

  • Be more aggressive with your vegetation modification and maintenance plan and more aware of the materials used to build the building, deck or any outbuildings.

  • Push fuel modification area beyond the 100-foot distance, if at all possible. A target for the extended fuel modification area would be between 150 feet and 200 feet.

  • Consider increasing the protection of your building by constructing a noncombustible retaining wall to help increase the set-back. When making future improvements, incorporate ignition-resistant features and materials into the building and surrounding landscape.