- 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
A team of California and Nevada fire scientists have produced a booklet with step-by-step guidance on retrofitting an existing home to be more resilient to fire.
Susie Kocher, UC Cooperative Extension forestry and natural resources advisor and co-author of the new guide, said some homeowners feel powerless to protect their homes against California's increasing wildfire threat.
“I'm happy to tell them that's not true. There are specific actions that we can all take to reduce the likelihood of our homes being burned in wildfire,” said Kocher, who lives in a forested area near Lake Tahoe. “We need to educate ourselves on the details of home construction that make homes less vulnerable to ignition.”
The free 20-page publication, How to Harden Homes against Wildfire (http://ucanr.edu/HomeRetrofitGuide) is now available online. It includes recommendations for 12 vulnerable components of homes in wildfire-prone areas, including roofs, gutters, vents, siding, windows, decks and fences.
In the past, agencies have focused on recommending changes in vegetation and establishing defensible space. However, Kocher said recent advances in wildfire science have exposed vulnerabilities of structures themselves.
“Managing vegetation and retrofitting the home are both needed to decrease wildfire risk and help our communities become more fire adapted,” she said.
CAL FIRE awarded funding to develop and publish the wildfire home retrofit guide, funding that is part of California Climate Investments, a statewide program that assigns cap-and-trade dollars to projects that aim to reduce greenhouse gas emissions, strengthen the economy and improve public health and the environment.
In addition to CAL FIRE, organizations that contributed to the document are University of Nevada, Reno Extension; University of California Cooperative Extension; Living with Fire, Tahoe; Tahoe Fire and Fuels Team; Tahoe Resource Conservation District; and Tahoe Network of Fire Adapted Communities.
The team also hosted three webinars to share home fire resilience information targeted to different audiences. Videos of the webinars are available on the Living with Fire YouTube Channel:
For the public: https://www.youtube.com/watch?v=YX114wpPwmg&t=327s
For building professionals: https://www.youtube.com/watch?v=ccIAIg6xONs
For fire educators: https://www.youtube.com/watch?v=lOsdyVSPxnA&t=177s
UC Agriculture and Natural Resources brings the power of UC to all 58 counties. Through research and Cooperative Extension in agriculture, natural resources, nutrition, economic and youth development, our mission is to improve the lives of all Californians. Learn more at ucanr.edu.
- 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.
- Author: Lenya Quinn-Davidson
Reposted from the Fire Adapted Communities Learning Network blog
I was nine years old when my dad's family home burned in the Oakland Hills Fire. As a country kid from one of the most fire-prone counties in northern California, I was no stranger to wildfire. Still, I remember the shock of driving through his childhood neighborhood in the weeks after the fire, seeing nothing but the skeletal remains of vehicles and homes — so different than the forest fires that I was used to back in Trinity County.
Those images came back to me a few weeks ago when I gave a presentation at a workshop in Redwood Valley, California. That community, which is in Mendocino County, suffered a devastating wildfire in October, during the same week that fires were burning throughout Sonoma and Napa counties. During the Redwood Valley Fire, nine people were killed and more than 500 structures were destroyed. Now more fires are burning in southern California, and in some ways, it seems that the human connection — the loss of lives, the loss of homes — is the defining feature of this year's fire season in California.
One of my close colleagues at the University of California Cooperative Extension, Yana Valachovic, has no doubt felt the human implications of the 2017 fire season. Her phone has been ringing off the hook for months because of her expertise and experience in home ignitions and home survival: concepts that people are desperate to understand and implement in light of the ongoing losses throughout the state.
In some ways, the research on home survival during wildfire is intuitive; most people understand defensible space concepts and the basics of fuels management. But there are so many ways that most of us could do better — ways that are well illustrated by my own friends, colleagues and family.
Yana talks about how even she — someone who studies this topic — stores paper bags full of her kids' old schoolwork in her attic, right next to the vents. And if you read the literature on this topic, you know that vents represent a major vulnerability during wildfire. Most homes burn from the inside out, meaning that embers make their way into the home through vents and other crevices, and they then ignite fuels inside the house. Once embers infiltrate, it's hard to slow them down — hence the photos we often see of blackened homes surrounded by green trees and intact neighborhoods.
Current research supports the use of finer mesh vent screens (typically a second screen behind the outer screen), and/or temporary vent covers during wildfire events. There is an impressive amount of information available on home venting and fire, including the desired fineness of screen meshes, the use of ridge vents and the appropriateness of unvented attics (PDF, 213 MB). Much of this work comes from the Insurance Institute for Business and Home Safety (IBHS). Steve Quarles leads IBHS's fire-related research program and has published a number of papers on this topic, including a new report, Vulnerability of Vents to Wind-Blown Embers.
Homes can also burn from the outside in, thanks again, in large part, to embers. A few years ago, when a wildfire came within a half mile of my mom's house, I found her gutters packed with dry leaves. This is a classic problem, and one that I was surprised to see at my own mom's house. How did we let the gutters fill up like that, knowing what we know? Gutters full of debris, if ignited, will provide direct flame and ignition to the edge of the roof; if the roof is not adequately protected by metal flashing, or if the gutter is below the roof edge exposing the vulnerable roof sheathing, it can be difficult to keep fire from spreading from the gutter into the house. In 2010, when Quarles was with University of California, he co-authored a great publication that discusses rain gutters, vents, roofing, decks and other home vulnerabilities (PDF, 4.87 MB).
There is also a fair amount of research on features adjacent or attached to the home — features like decks, fences and landscaping (PDF, 416 KB). Still, on a recent trip to a research station in southwest Georgia (a place known for its fire science research and active fire management), I was surprised to see that the landscaping around every building had a thick mulching of longleaf pine needles — literally one of the most flammable types of leaf litter in the world. It looked great but wouldn't be particularly helpful if a fire came through. And IBHS wildfire demonstrations, like this one from 2011, have shown that mulches and other near-home landscaping can become serious points of weakness during wildfire. (I highly recommend checking out their video demonstrations if you haven't before; they have a lab where they actually burn down full-sized homes.)
Now I know that this information is likely old news to many of you; I hesitated to write about this topic because our readership is probably fairly fluent in the research on home ignitions and survival. But the images of Yana's attic full of well-cured paper, my mom's gutters full of leaves, and the pine needle mulch at the research station in Georgia reminded me that we all have more we can do — even if we're well-versed in how homes burn. Home hardening is, of course, only one facet of fire adaptation, but this year's fires reinforced the importance of all efforts at all scales, from the vent and the gutters to the community wildfire protection plan and the prescribed burn.