Skip to main content

Defensible Space

In January 2005 a new state law became effective that extended the defensible space clearance around homes and structures from 30 feet to 100 feet.

Proper clearance 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 wildland fire.

Why 100 feet? More and more homes are being built in the space between the urban area and the wildland area. This area is called the Wildland / Urban Interface. There are not enough firefighting resources in the County to have a fire engine placed at every structure in the path of even a moderate sized wildland fire. Add wind, steep topography, and narrow winding roads and it becomes even more difficult. A 100 feet defensible space will give your home a chance to survive if the fire arrives at your home before firefighting resources do. When firefighting resources are at your home the 100 feet defensible space will provide for added firefighter safety. Too many firefighters have been killed trying to protect homes without adequate defensible space.

The 100 feet defensible space is not expected to be an arid wasteland. To the contrary, the area from 0 to 30 feet is called the “Lean, Clean and Green Zone”. Clearing this area surrounding your home is critical. This area requires the greatest reduction in flammable vegetation.

  • Remove all flammable vegetation and any dead or dying plants within 30 feet of each building or structure. You may keep single trees or other vegetation that are trimmed of all dead and dying foliage and are well pruned and maintained.
  • Additional steps you can take are selecting less flammable plants for your Lean, Clean and Green Zone: shorter plants (less than 2 feet) are safer than taller ones. If kept green, herbaceous plants (grass and non-woody flowers) are better choices than shrubs and trees. If planting shrubs and trees, choose deciduous ones (trees that shed their leaves) over evergreens. Avoid planting juniper, pine and palms.
  • Remove tree limbs that are touching the house or deck, or are within 10 feet of the chimney. If limbs are encroaching on overhead lines, contact your telephone or power company for removal.
  • Use hard surfaces (concrete, stone, asphalt, brick, etc.) in your landscaping.
  • Clear ALL flammable vegetation from within 10 feet of propane tanks.

The area from 30 to 100 feet is called the “Reduced Fuel Zone”. The Reduced Fuel Zone is the remaining 70 feet (or to the property line). Decrease fuel in the Reduced Fuel Zone.

  • Surface litter consists of fallen leaves, needles, twigs, bark, cones, pods, small branches, etc. Remove loose surface litter so it does not exceed a depth of three inches.
  • All logs and stumps should be removed unless they are embedded in the soil. If you keep an embedded log, remove nearby vegetation.
    A standing dead tree (snag) may be kept for wildlife providing there is only one snag per acre, and if the snag were to fall, it would not reach buildings or structures and would not land on roadways or driveways.
  • Provide fuel separation and treatment. Guidelines for fuel treatment as published by CAL FIRE are designed to reduce the spread of wildfires.
  • Choose option 2a or 2b below. The best option for your property will be based on its characteristics (slope, vegetation size, vegetation type like brush, grass, trees, etc., and other fuel characteristics). Properties with greater fire hazards will require larger separation between fuels. For example, a property on a steep slope with larger vegetation will require greater spacing between trees and shrubs than a level property that has small, sparse vegetation.
2a: Grasses

Ideally, grass should not exceed four inches in height. In situations where these fuels are isolated from other fuels or where they are necessary to stabilize soil, grasses and forbs may reach a height of 18 inches.

2a: Horizontal Clearance for Shrubs and Trees

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. Click here to see a chart for an estimation of clearance distance. Any questions regarding requirements for a specific property should be addressed to your local fire official.

2a: Vertical Clearance for Shrubs and Trees

Low branches create “ladders” from the ground fuels to the trees. To determine the proper vertical clearance between shrubs and the lowest branches of trees, use the formula below.

SHRUBS – From edge of one shrub to the edge of the next

Flat to mild slope (0% to 20% slope) Two times (2x) the height of the shrub (Two shrubs 2′ high should be spaced 4′ apart)
Mild to moderate slope (20% to 40% slope) Four times (4x) the height of the shrub (Two shrubs 2′ high should be spaced 8′ apart)
Moderate to steep slope (greater than 40% slope) Six times (6x) the height of the shrub (Two shrubs 2′ high should be spaced 12′ apart)

TREES – From edge of one tree canopy to the edge of the next

  • Flat to mild slope (0% to 20% slope) n t 10 feet
  • Mild to moderate slope (20% to 40% slope) 20 feet
  • Moderate to steep slope (greater than 40% slope) 30 feet
2b: Defensible Space with Continuous Tree Canopy

To achieve Defensible Space while keeping a larger stand of trees with a continuous tree canopy, adhere to the guidelines below:

  • Prune lower branches of trees to a height of 6 to 15 feet from the top of any vegetation/shrubs below the tree to the lowest branches of the tree. If the tree is small, remove the lower 1/3 of its branches. Properties with greater fire potential such as steeper slopes or more severe fire danger will require pruning heights in the upper end of this range.
  • Remove all ground fuels greater than four inches in height. Single specimens of trees or other vegetation may be kept if they are well-spaced, well-pruned and create an overall condition that avoids the spread of fire to other vegetation or to structures.
Remember… creating defensible space is YOUR responsibility and it is required by law*.

*Compliance to PRC 4291 is required by any person who owns, leases, controls, operates or maintains a building or structure in or adjoining any mountainous area, forest-covered lands, brush-covered lands, grass-covered lands or any land that is covered with flammable material and is within the State Responsibility Area. PRC 4291 requires 100 feet of Defensible Space (or to the property line if less than 100 feet) from every building or structure that is used for support or shelter of any use or occupancy. Owner, lessee or operator must also comply with all existing environmental protection laws and must obtain all necessary permits. Contact your local resource or planning agency officials to ensure compliance with federal, state and local requirements. Contact your local CAL FIRE office, fire department, or Fire Safe Council for tips and assistance.

Join our mailing list