- Author: Pam Kan-Rice
In 2018, the Camp Fire destroyed nearly 19,000 structures in Northern California, including most of the town of Paradise. The structures left standing by the conflagration provided researchers an opportunity to investigate how housing arrangement – such as the size of the lot, the distance to a neighboring home, and surrounding vegetation – influenced which homes survived. They also looked at whether changes to the California Building Code in 2008, through the addition of Chapter 7A, improved the chances of homes built in the wildland-urban interface to withstand wildfire.
Both housing arrangement and surrounding vegetation likely influenced the survival of homes during an extreme wildfire, according to new research from the USDA Forest Service and the University of California Agriculture and Natural Resources analyzing the Camp Fire aftermath, which will be published Oct. 3 in the journal Fire Ecology.
“Our team found a reason for hope and information that can help Californians, building contractors and policymakers better prepare for future fires,” said co-author Yana Valachovic, University of California Cooperative Extension forest advisor.
The 2008 code, which applied to the city of Paradise, requires the installation of vents that resist flames and embers and other elements that help harden a home to wildfire. This chapter of the California Building Code added requirements for construction materials to California's existing two-zone fuel and vegetation modification guidance, known as “defensible space,” which applies to the vegetation and fuels out to 100 feet from a home.
The researchers found that the age of the home was a significant factor in predicting survival. But the key year wasn't 2008. Improvements in performance happened earlier. Only 11% of single-family homes built in or before 1996 survived, compared with 40% for homes built after 1996. Older homes were, on average, placed closer together and had more overstory tree growth near the home. Overall, the greater the distance between structures, the lower the likelihood of a home being destroyed by the Camp Fire. And the less overstory tree canopy cover, the higher the likelihood of a home surviving.
During a wildfire, structures can be threatened by the flaming front of the fire and by embers that are lofted ahead of the fire and land on fuels such as vegetation or mulch next to the house, igniting new fires. Embers can also enter homes through open windows or vents. Heat radiating from adjacent burning buildings or vegetation can also impact home survival.
“Despite the unpredictable nature of wildfire, strong associations with home arrangement and overstory vegetation cover indicate home survival is at least somewhat predictable,” said lead author Eric Knapp of the USDA Forest Service. “The silver lining is that this also suggests steps can be taken to substantially improve the odds of homes surviving a wildfire.”
One of the biggest drivers of home loss in the Camp Fire was the heat radiating from the large number of structures that burned. Over 73% of homes destroyed in Paradise had a structure burn within 59 feet. The distance to the nearest destroyed structure or total number of destroyed structures within 328 feet was a primary predictor of home loss.
“Exposure to the heat of a nearby burning structure can break glass in a window, for example. Once the glass is broken, embers or flames can enter the house,” said co-author Steve Quarles, emeritus UC Cooperative Extension advisor and retired chief scientist for the Insurance Institute for Building & Home Safety.
This finding suggests that denser developments, built to the highest standards, may protect subdivisions against radiant heat from a vegetation fire, but density may become a detriment once buildings ignite and radiant heat loads increase as well as the increased potential for direct flame contact.
“This research suggests a strong neighborhood effect, where the condition and proximity of an outbuilding or a neighbor's home can have a significant influence on a building's survival given the radiant heat exposure from a neighboring building burning,” Valachovic said.
Tree canopy cover was also associated with home loss, with a higher probability of home survival where tree cover was moderate or less.
“Trees provide shade, which is important where summers are hot. But to have the amenities trees provide without undue fire hazard, the key is to clean up the leaves and dead wood trees produce,” said Knapp. “This includes keeping roofs, gutters, garden beds adjacent to the structure and spaces under attached decks, free of leaves.”
The researchers detected no significant increase in survival for homes built from 2008 to 2018, under the new building code, compared to homes constructed during an equal time period, 1997 to 2007, immediately preceding the adoption of the new code. Houses built during the last two decades resisted wildfire better than older homes, indicating an overall improvement in common construction standards and the performance of building materials.
“It is important for Californians to understand that homes and immediate surroundings need to be well-maintained to resist embers, survive extended radiant heat exposures and minimize direct flame contact,” Quarles said. “Fortunately, all building codes get better with time and Chapter 7A is no exception – Californians have benefited from it. California's Building Code is reviewed every three years, and it is evolving as new knowledge becomes available based on research and post-fire assessments.”
To enhance wildfire protection at the neighborhood scale, the researchers recommend coordinating efforts with neighbors.
“Because ember ignition of one house can put neighboring houses at risk, it is critical that fuel reduction happens at a community scale. Living with fire means doing all things possible to prevent one's house from catching fire,” said Valachovic.
There are simple actions that homeowners can take to protect their homes.
“From retrofitting with vents that resist ember entry or using tempered glass windows, to the simple things, like not placing bark mulch or woody plants next to homes, and using gutter guards to minimize leaf and needle accumulation in gutters, all will improve the chance of home survival,” Quarles noted. “It is a matter of how we choose to live in this environment.”
“Housing arrangement and vegetation factors associated with single-family home survival in the 2018 Camp Fire, California” by Knapp, Valachovic, Quarles and Nels G. Johnson is published in the journal Fire Ecology at https://fireecology.springeropen.com/articles/10.1186/s42408-021-00117-0.
For more information:
- Author: jeannette warnert
The unspeakable loss of human life and the serious challenges being faced by survivors has dominated the Camp Fire conversation. Now, UC Cooperative Extension is beginning a dialog with many agencies involved to understand how such tragedies can be prevented in the future.
UC Cooperative Extension fire scientists and representatives of many California organizations conduct fire behavior research, study forest treatments – such as prescribed burns, timber harvest and mastication – and share best practices for home and community preparation. In the Butte County area where the Camp Fire took place, cooperating agencies include CalFIRE, the U.S. Forest Service, the Butte County Fire Safe Council, the Yankee Hill Fire Safe Council, Sacramento River Watershed Program, the Sierra Nevada Conservancy, the Bureau of Land Management, and others.
While the Camp Fire was devastating, it could have been far worse. Working together for decades, the partner agencies have improved community safety and resilience.
They have educated the public about defensible space, fire resistant homes, and evacuation plans. They have coordinated fuels treatments along evacuation routes and around the communities. Through their actions, they saved many lives and structures, protected the town's drinking water supply, and in some cases, provided access for hiking in areas that had been overgrown by brush.
“When you drive for miles through blackened, burned trees and then arrive in a thinning project area full of green tree tops, you know that these efforts are worth it, we are having success and we can make a difference together,” said Calli-Jane DeAnda, executive director of the Butte County Fire Safe Council.
Because of the Camp Fire tragedy, the partner agencies learned many lessons that can inform future maintenance and treatments to improve fire resilience in Butte County and other wildland areas. Kate Wilkin, the UC Cooperative Extension fire advisor for Sutter, Yuba, Butte, and Nevada counties, is able to point to projects implemented in the Camp Fire zone that saved lives and structures.
For example, one family in Paradise was featured by the news media for their successful advance fire planning, which even included the installation of sprinklers on top of the house.
“When I think about what saves a house, a sprinkler is a cherry on top of the cake,” Wilkin said. “If a house is constructed with a combustible roof and siding, if unprotected vents allow embers to get into the attic, or the landscape is not maintained, a sprinkler isn't going to save the house. The sprinkler's power from the grid or a generator will likely fail. High winds may even prevent the sprinkler's mist from hitting the house.”
Rather, passive resistance to fires through better building design, materials and maintenance greatly reduce structure loss.
“Maintenance is an unsung hero of fire resilience,” Wilkin said. “Individual actions at our homes matter.”
First 5 feet around a structure
State law requires homeowners in wildfire areas to clear 100 feet of defensible space around their structures. Most towns in wildfire-prone areas also have their own defensible space codes. Wilkin said where she lives in Grass Valley, anyone with less than an acre of land must maintain their entire property as defensible space.
This guideline is a start, but there is more that people who live in wildfire-prone areas can do to make their homes resilient to fire. UC Cooperative Extension scientists recommend creating a five-foot buffer immediately surrounding the home almost completely devoid of plants and anything that can burn - including wooden fences, firewood, deck chairs and pillows, brooms and other wooden tools.
This extra precaution is important as embers from a distant wildfire can land on or adjacent to a house and ignite combustible items which in turn ignite the home. It was evident in the Camp Fire that the first five feet around homes was a critical factor in the survivability of structures.
The zone can include noncombustible materials such as rock mulch, stone pavers, cement, bare earth, gravel or sand. Low combustibility materials, such as irrigated and maintained lawn or herbaceous plants less than five inches high, are okay. All leaves, needles or other vegetation that falls in this five-foot zone must be removed during the fire season.
“The non-combustible space adjoining the house may be the difference between losing it and all the contents to a wildfire versus returning to the property with the home unscathed,” Wilkin said.
Community fire resilience
Fire survival measures can also be taken at the community level.
In Paradise, the Butte County Fire Safe Council funded CalFIRE crews to thin a number of areas in the watershed below Paradise Lake in 2013 and 2014. Taking these actions allowed an area for firefighters to start a defense and start putting out the flame front, Wilkin said.
“A CalFIRE chief told residents, ‘You provide the offense, we provide the defense.' Homeowners and communities need to get everything set up for successful firefighting,” she said.
Forest thinning has the added benefit of improving recreational opportunities. Near Magalia Pine Ridge School, an 11-acre mastication project in 2018 funded with $30,000 from the Butte County Fire Safe Council cleared overgrown vegetation around the school. This helped strengthen the area's public assembly location, which was identified on the community's evacuation map, and opened up access to a forest hiking trail that was blocked by tangled brush.
The open space dramatically slowed the raging Camp Fire when it approached the school, which is now one of the only schools open in the Paradise Ridge community.
Forest thinning also protected the drinking water for the town of Paradise. A combination of projects undertaken by U.S. Forest Service, Sierra Pacific Industries and the Butte County Fire Safe Council aligned to allow fire fighters to combat the fire and ensure that the source of drinking water was protected.
Concow wildfire safety zone
In 2013 and 2014, the Butte County Fire Safe Council and Yankee Hill Fire Safe Council created a wildfire public assembly safety zone in Concow. The work was completed by inmate crews. During the Camp Fire, dozens of lives were saved when sheriff deputies, firefighters and citizens were able to shelter in the area.
“Wildfire safety zones are pretty uncommon and we may want to create more in wildfire prone areas,” Wilkin said. “But there is a hitch.”
CalFIRE is reluctant to designate temporary refuges because they don't want people to rely on them in place of evacuation. During a quick-moving firestorm, it could be an area where people can shelter if they cannot get out.
“It's a complex and dangerous puzzle,” Wilkin said. “In Australia, they had a similar idea and some places where people sheltered in a fire caused them to die.”
Wilkin is working with Paradise parks to identify areas ahead of time with enough space to meet new national firefighter standards to protect people's lungs from superheated air.
“Historically, we thought sufficient space was four times as great as the flame heights. If you have a Ponderosa pine that's torching 150 feet high, you would need 800 feet around the people,” Wilkin said. “New research has found that the safety zone calculation must also consider potential wind speed and slope. Significantly more space may be needed.”
- Author: Yana Valachovic
Shades of brown and grey cast over bricks, cement, remnants of metal roofs and steel beams from manufactured and modular homes, collapsed stucco walls, BBQs, shells of washers and driers, along with an occasional tea pot—that is what you can see in and amongst living, but singed Ponderosa pine and California black oak trees where the Camp Fire burned. How did California's most deadly fire happen and what might be done differently to ensure a better outcome? These are difficult questions that California will wrestle with for a long time to come.
Last week I was able to tour some of the burned area in Paradise and Magalia to evaluate why some homes survived and others did not. This gave me a chance to look at homes that survived largely on their material selection, design details, the owner's maintenance efforts, and not necessarily with the aid of a fire crew or resident that stayed. Many of the buildings that were burned were lost on the first day or two of the fire while emergency response was focused on evacuating the communities. It will take months to make sense of this mess and tragedy, but during my tour some conditions rang true to me.
- Wildfire is not uniform. Not all fires are the same and not all houses experience the same type of fire. When you are looking at home losses and survivors, keep in mind that each home may not have had the same fire exposure. Some homes experienced significant ember exposure, while others ignited because their neighbor's home succumbed to fire and the heat of their neighbor's house caught their house on fire, while others were protected from the wind and its deadly embers. Paradise and Magalia have blocks and blocks of nothing but foundations, but amongst these bleak conditions are a few intact or partially damaged homes that have a story to tell.
- We saw homes that survived that had upgraded attic and foundation vents that meet the California building code for construction in wildfire prone areas. Some of these houses also included some extra efforts where vegetation and combustible mulch was virtually eliminated in the area immediately adjacent to the home. Our inspection team included UC's Dr. Steve Quarles, a national expert in fire-safe construction, who interpreted this to mean that meeting the 2008 Chapter 7 A standards, coupled with the enhanced defensible space, likely made the difference to ward off the assault of the ember-driven Camp Fire. We found evidence that burned homes in Paradise had ¼” mesh foundation and under-eave vent screens. Research has shown that these larger size screens let embers penetrate the attic and ignite the house from within. The 2008 California building code standards specify screen mesh size between 1/8” and 1/16”-inch, or vents that demonstrate their ability to resist embers and flames.
- Our tour also confirmed that landscaping plants and wood mulch placed right next to the house creates vulnerability. While looking at the rubble of a home, it can be difficult to tell what happened; however, we saw several surviving houses with broken glass or otherwise damaged dual-pane windows that experienced heat exposures sufficient to crack glass in the windows, but the home still survived during these first two days when fire crews were rightly focused on community evacuation and not structure protection. For the houses that did not survive, we can interpret that in addition to the vulnerabilities in vents or a roof, heat can easily break glass in windows, especially if those windows are single pane, and can likely created a pathway for fire to enter the houses.
- Home placement makes a difference. A home at the top of a canyon or gulch can easily be overwhelmed by wildfire by taking on additional heat as the fire approaches and being blasted with embers. This is not a new concept, but the homes in the broader Paradise region were especially vulnerable when they were located above these gulches and canyons. Enhanced vegetation management is highly recommended that includes a 5-foot non-combustible zone immediately adjacent to the home.
Our team, which also included Dr. Eric Knapp from the USDA Forest Service Pacific Southwest Research Station, has been able to do a quick analysis of home losses by year of construction in Paradise. This cursory analysis shows that many homes built after the 2008 wildfire standards were adopted were lost during this fire, however, without knowing the specific details of each home (e.g., maintenance practices, proximity to other building, etc.), these statistics can be misleading. We will continue to work through the available data to try to look for patterns, however, in the meantime, it seems clear to me that the new construction standards can reduce the probability of ember intrusion and may have helped for some homes in Paradise. This week a new study reported that complying with these standards was not considerably more expensive. Additionally, the codes that help guide construction in California's wildfire-prone areas are dynamic and will be informed by the 2017 and 2018 wildfire seasons.
For me thinking about Paradise in the abstraction was easy. Visiting it was different. The name says it all. After my visit I could understand why someone would choose Paradise or Magalia; the views are awesome, the air is clear, the forest and woodlands are amazing. I can only imagine that the community was (almost) perfect. Rebuilding a more resilient community will take considerable thought, effort, and some radical new ideas.