Defensible Space

Your First Line of Defense

Defensible space could be the most valuable tool in protecting your home from wildland fires. In essence, this is the buffer between your home and the wildland that will either stop a fire or slow it to the extent that fire fighters can save your home. Residents of high risk areas are painfully familiar with aerial photos of homes sitting intact on a block of charred skeletons — homes cleared of brush with specific landscaping that retards or resists flames.

At one time, 30 feet of defensible space was the rule of thumb. In some areas, that space increases to 100 or 150 feet. The best judge of the amount of defensible space required in your specific situation is your local fire department. Like the tips and recommendations in our home fire safety pages, the higher the risk in your area and your situation, the wider the defensible space should be.

There are a few anomalies we need to mention before we get into general guidelines. Some communities have codes that protect natural habitat even on privately owned land. In consideration of fire danger, selective thinning of native growth may satisfy both the fire marshal and the habitat requirements. Check with local agencies if there are habitat restrictions on your property.

One element of defensible space is the clearing of overhanging tree branches and heavy brush five feet from driveways and 10 or more from roads. What if the brush that threatens to choke off the road to your property is privately owned and undeveloped? Check with your local fire department. If the brush creates a serious danger to residents, the owner can be contacted and asked to clear the 10 foot buffer.

Now, how to create defensible space around your home:

• Remove or radically thin flammable native vegetation within your defensible space, whether that space is 30 or 150-feet. The most logical approach is to first determine your fire risk, taking into account slope, wind patterns, etc. If your risk factor is high, multiply your defensible space by 150 percent. Another approach involves landscaping with fire resistant plants within the first 30+ feet around your home and fuel reduction and pruning of both natural vegetation and landscaping to 100 to 150 feet around your home.
• Select fire resistant plants to landscape the area.
• Vary the height of your landscaping and space it out. The taller your plants or trees, the farther apart they need to be. One recommendation is to space trees 10 to 15 feet apart measured at the widest point of mature branch spread.
• Avoid tall shrubs and vines growing against structures.
• Skirt or limb mature trees to one-third of the height. This requires cutting the lower branches. If the tree is 15 feet tall, remove branches five feet up the trunk. Again, depending on your risk factor, some guidelines increase the height of skirting.
• If shrubs and trees create a ladder effect, shrubs adjacent to increasingly taller trees, eliminate that ladder by selectively removing some of the “rungs” or more aggressive skirting of the taller trees.
• Remove dead limbs overhanging your roof and any limbs within 10 feet of your chimney.
• Avoid planting trees that will interfere with electrical lines. If tree branches are growing too close to power lines, call the utility company to prune. Don’t attempt this yourself.
• If you have a heavily wooded area on your property, remove the weakest trees and leave a mix of older and younger trees. Remove low brush and dead growth.
• Check with the local fire department for restrictions on open burning of vegetation waste. Some areas require burn permits and place restrictions on days and times of day burning is allowed. A preferred way to dispose of vegetation debris is at area green waste dumps. Remove scrap lumber from the property.
• Stack firewood and construction materials 30 feet from any structure and clear vegetation within 10 feet of those piles. If you have a propane tank on your property, clear vegetation 30 feet around the tank.
• Keep the landscaping within your defensible space healthy with regular maintenance and irrigation.
• Clear flammable vegetation five feet from your driveway and 10 feet from your road frontage. Prune branches that overhang either your driveway or the public roadway.

Tagged as: Defensible space, wildland fire defense