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How Topography Influences Wildfire Risk

Wildfires burn up a slope much faster and flame lengths can also be very long. Homes located midway or at the top of a slope are at a higher risk from increased flame length, so it is wise to increase the defensible space around the home. 

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.  While moderate or steep slopes greater than 20%, are very dangerous, any slope can potentially increase the amount of heat a structure will be subject to during a wildfire.

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.

Plant Spacing Is Affected By Slope

Uncleared ground fuels provide an open freeway for the rapid spread and increased intensity of fire. Clearance between shrubs should be 4 to 40 feet depending on the slope of the land and size and type of vegetation.

Check the chart below for an estimation of clearance distance. Any questions regarding requirements for a specific property should be addressed to your local fire official.

horizontal plant spacing on a slope

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