Wildfires: masonry structures withstand Southern California: Portland cement stucco and masonry veneers meet tough code requirements

Masonry Construction, Feb, 2005 by Mark Kluver

I visited Southern California in 1993 to investigate the aftermath of the wildfires that occurred in October. Almost exactly ten years later to the day, wildland fires again swept across large swaths of Southern California from north of Los Angeles to the Mexican border.

What sets the recent fires apart from those ten-years earlier were their size and the amount of destruction they caused, burning more than twice the acreage (745,800 versus 333,700) and destroying well over three times as many dwellings (3640 versus 971). In addition, 33 commercial properties and 1141 other structures were destroyed by the time the fires were subdued by wet, cool weather.

State officials estimated that damages from the 2003 fires exceeded $2 billion, which is the largest property loss from wildfires in the state's history. Of greater significance, 23 people perished and 174 were injured.

Contributing factors

Many factors contributed to the tremendous loss of life and property--some new, but most recurring. For example, in late October or early November of most years, hot winds blow off the upper deserts and through the dry Southern California mountain ranges. A new twist in 2003 was that the area's forests had experienced a multi-year drought, followed by a bark beetle infestation that had weakened or killed huge stands of trees. The drought also created enormous amounts of fuel in the form of kiln-dried chaparral shrubs on lands near the Pacific Ocean, especially in San Diego County. Given these conditions, a spark was all that was needed to ignite a conflagration that the hot, dry winds could spread uncontrollably.

There is no question that population growth and development in urban/ wildland interface areas also increased the risk of catastrophic fires. "There is almost a direct correlation between growth and the number of ignitions," said University of California, Berkeley, Professor Tim Duane, whose statistical survey of California's Sierra Nevada mountain range indicated that a doubling of population may be responsible for a 5000% increase in property damage.

Also, some housing was built in so-called "indefensible locations," such as Palmer Canyon in the foothills of the San Bernardino National Forest, where 47 houses once stood but only four remain. Other examples of indefensible locations include the narrow, miles-long canyon containing the Hook Canyon community where 350 homes burned and Crestline, a neighboring community that contained dozens of closely spaced wooden houses surrounded by dry, brittle pine trees which overhung roofs and porches.

The San Bernardino Mountains had not experienced a severe burn in nearly 100 years, in part due to the U.S. Forest Service's policy of suppressing fires, which left the land with an unprecedented buildup of fuel. Local politics also contributed to the problem. For example, in the community of Lake Arrowhead a homeowners association had a long standing policy of banning property owners from cutting trees in order to help preserve the area's natural beauty. The ban was lifted a year ago and some residents did what they could to remove the dead pines, but the debris was too dense.

Mitigation features

Despite the high losses experienced in the 2003 Southern California wildfires, the results could have been much worse if not for changes made in the wake of the 1993 fires. While many homes were lost, the adoption of local ordinances requiring special protection against wildland fires was critical to the preservation of tens of thousands of other dwellings along the several hundred miles of the fires' perimeters.

Local adoption was helped along in part when state lawmakers passed the Bates Bill following the devastating Oakland Hills fire in October 1991. That legislation required the state fire marshal to designate high-hazard fire-risk zones and permitted local governments to require stricter building standards within these areas.

Local jurisdictions throughout California have set different standards for building in high-hazard fire-risk zones. Most of the homes recently built in areas of high risk have at least some special features common to the International Urban-Wildland Interface Code (IUWIC).

The special features that appeared to have provided the most protection in the recent wildfires were noncombustible (or Class A) roofs and noncombustible exterior wall surfaces, such as masonry veneers and portland cement stucco which easily, aesthetically, and economically satisfy the provision of the IUWIC. Other mitigation strategies such as protecting roof eaves, decks, and unenclosed underfloor areas with noncombustible materials are now more common than prior to 1991.

Another feature that was critical to protecting dwellings from the firestorms was the more prevalent use of defensible spaces around individual dwellings or subdivisions. Defensible space is defined in the IUWIC as "an area--either natural or man-made--where materials capable of allowing a fire to spread unchecked have been treated, cleared, or modified to slow the rate and intensity of an advancing wildfire and to create an area for fire suppression."