Protecting homes in the wildland urban interface


Wildland fire is an important ecological disturbance similar to that of earthquakes, hurricanes, and floods. Although fires are an integral part of natural ecosystems, they are categorized as “catastrophic” when human lives and property are put at risk. As more and more people move into wildland areas, this natural process has become a dangerous enemy. The wildland urban interface, where residential areas meet natural areas, poses the greatest challenge and holds the highest priority in fire management.

This home in a ponderosa pine forest has a metal roof, concrete deck and non-flammable siding to protect it from wildfire.
The story is different in ponderosa pine forests east of the Cascades, where dry conditions and frequent summer lightning start many fires. In these areas, homeowners need to take precautions to minimize their risks, rather than expecting the Forest Service and local fire department to protect them.

Forest Service scientists have studied conditions that start homes on fire from the outside. The major cause of home loss is flammable roofing materials. Roofs and wooden decks can easily catch fire from windblown embers or from direct contact with nearby trees, shrubs or neighboring structures. Case studies show that embers lofted from over a kilometer away can start roofs on fire. Surprisingly, these homes often burn without igniting the surrounding vegetation!

In addition to having noncombustible roof and decks, keeping a zone of low-fuel density (clearing vegetation, pruning trees, removing stacked firewood) within 30 feet of all structures is another way to reduce fire risk. Analyses of home losses in southern California indicate that “vegetation clearance of at least 10 meters was associated with a high occurrence of home survival.” 1 Experimental crown fires also did not ignite wood siding at 10 meters, and computer modeling indicated that walls of flame further than 40 meters could not ignite buildings.

“This research indicates that home losses can be effectively reduced by focusing mitigation efforts on the structure and its immediate surroundings.” 1 It also implies “that wildland fuel reduction for reducing home losses may be inefficient and ineffective. Inefficient because wildland fuel reduction for several hundred meters or more around homes is greater than necessary for reducing ignitions from flames. Ineffective because it does not sufficiently reduce firebrand ignitions.”

This astounding revelation should direct the expenditure of effort and dollars to protect people and their property from wildland fires. In the long run, it will save taxpayers millions in firefighting funds and insurance premiums. Firesafe communities will also facilitate prescribed burning of wildlands without the high risks of damaging residential structures.