Protecting Your Home From Wildfire
It doesn't have to happen
THE 3 FACTORS
1. Flying embers ignite most homes, because most homes are flammable.
It's not a "wall of flame" that destroys homes, but embers that can travel a mile or more ahead of the fire front.
The importance of embers is nothing new. Wayne Tyson highlighted this issue after 2003 during the Cedar Fire.
The notion that if 100 feet of defensible space is good, then 200-300 feet must be better is false. Creating large areas of clearance with little or no vegetation creates a "bowling alley" for embers. Without the interference of thinned, lightly irrigated vegetation, the house becomes the perfect target for embers.
To make matters worse, when a fire front hits a bare fuel break or clearance area, a shower of embers are often released.From: Koo, E, R.R. Linn, P.J. Pagni, and C.B. Edminster. 2012. Modeling firebrand transport in wildfires using HIGRAD/FIRETC. International Journal of Wildland Fire 21: 396-417. Key Point: Fire will exploit the weakest link. Many homes with adequate (or excessive) defensible space have still burned to the ground because embers have entered through attic vents,
Federal grants are available to help communities retrofit homes to make them more fire safe. Details of these FEMA pre-disaster grants can be found here. The process is complicated, but it can be accomplished. Note: This is for a community, not for individual homeowners. A non-profit fire safe council, or some other non-profit, will need to apply. The California communities of Big Bear and Idyllwild provide an excellent example of this program.
Additional information on the impact of embers is available in the following publications:Maranghides, A. and W. Mell. 2009. A Case Study of a Community Affected by the Witch and Guejito Fires. National Institute of Standards and Technology Technical Note 1635. US Department of Commerce.
A Wet Home
Keeps the Embers and Flames at Bay
2. It's not the wildland vegetation, it's the location.
Syphard and her coauthors gathered data on 700,000 addresses in the Santa Monica Mountains and part of San Diego County. They then mapped the structures that had burned in those areas between 2001 and 2010, a time of devastating wildfires in the region.
Buildings on steep slopes, in Santa Ana wind corridors and in low-density developments intermingled with wild lands were the most likely to have burned. Nearby vegetation was not a big factor in home destruction.
Looking at vegetation growing within roughly half a mile of structures, the authors concluded that the exotic grasses that often sprout in areas cleared of native habitat like chaparral could be more of a fire hazard
From the Los Angeles Times, 6/16/12
For a concise summary of the study:USGS Briefing Paper
The full paper:Syphard, AD, JE Keeley, A Bar Massada, TJ Brennan, VC Radeloff. 2012. Housing arrangement and location determine the likelihood of housing loss due to wildfire. PLoS ONE 7(3): e33954. doi: 10.1371/journal.pone.0033954
3. Defensible space can work, but beyond 100 feet is counterproductive.
1. The most effective measures to reduce structure losses are to “reduce the percentage of woody cover up to 40% immediately adjacent to the structure and to ensure that vegetation does not overhang or touch the structure.”
2. There is no additional structure protection provided by clearing beyond 100 feet, even on steep slopes, and the most important treatment zone is from 16‐58 feet.
The concise USGS summary of the study.
The full study: Syphard, A.D., T.J. Brennan, and J.E. Keeley. 2014. The role of defensible space for residential structure protection during wildfires. International Journal of Wildland Fire 23:1165‐1175.
WARNING If you have received a weed abatement or clearance notice from a local fire agency or a private contractor, your ownership of your home may be at risk. Please visit our page about how Fire Prevention Services, Inc. caused one man to lose his home while government officials looked the other way.
Creating a "Defensible Space" Around Your Home:
The Difference Between Rational Action and Overreaction
The basic rule of thumb is to reduce the level of vegetation within the 70-foot zone so that about half of the ground remains covered by a vegetative canopy. This also maintains some habitat value.
Unfortunately, the term "clearance" is frequently used when referring to the 100-foot defensible space zone, leading people to think all vegetation must be removed down to bare soil. This is why the city of San Diego Fire and Rescue Department has replaced the word "clearance" with "thinning" when referring to vegetation management around homes. Bare soil clearance not only unnecessarily compromises large amounts of native wildlands and increases erosion, but will lead to the growth of weeds in the now disturbed soil. These weeds are considered "flashy fuels" which actually increase fire risk because they ignite so easily.
This document from the San Diego City Fire Department provides a reasonable plan to reduce fire risk around your home WITHOUT unnecessary, excessive clearing. It shows an excellent diagram of what an area looks like after proper thinning.
There is no one answer to reducing fire risk
- Location- Flame/ember-resistent building design- Fuel management (defensible space)
It is not just about managing vegetation.
VIDEO: Dr. Jack Cohen explainswhat causes most homes to burn down - it's not heat, but the embers.
For fire safe native plant selections, the Tree of Life Nursery and Las Pilitas Nursery can provide some excellent suggestions. An article by Greg Rubin will also offer some useful guidance on native plant landscaping. During the 2007 Grass Valley fire near Lake Arrowhead, approximately 199 homes were destroyed or damaged. This was despite the fact that the US Forest Service had thinned the surrounding forest and removed vegetative fuels. The main cause of the losses was that individual homeowners failed to understand that vegetation management is only one part of the fire risk reduction equation. Fire will exploit the weakest link, and did so in Grass Valley. In the detailed report on the fire, the USFS (2008) wrote,
“Post-fire visual examination indicated a lack of substantial fire effects on the vegetation and surface fuels between burned homes. Lack of surface fire evidence in surrounding vegetation provides strong evidence that house-to-house ignitions by airborne firebrands were responsible for many of the destroyed homes.”