Data shows building codes can reduce vulnerability of homes in wildfires

Slave lake burned homes
Burned homes in Slave Lake. May 16, 2011. Alberta, Canada. CTV.

Researchers have found that building codes based on lessons learned during the deadly 1991 Tunnel Fire in the Oakland Hills of California can reduce the vulnerability of homes to wildfires.

In a paper titled Mandatory vs. voluntary adaptation to natural disasters: the case of U.S. Wildfires, authors Patrick W. Baylis and Judson Boomhower describe how they scoured property and wildfire records to identify which homes were constructed under building codes requiring enhanced resistance to wildfires.

Chapter 7A of the California Building Code which went into effect in 2008 requires certain fire resistance measures, including exterior construction materials used for roof coverings, vents, exterior walls, and decks. It applies to new construction of residential and commercial buildings in designated fire hazard severity zones.

The researchers discovered that a 2008 or newer home is about 16 percentage points (40%) less likely to be destroyed than a 1990 home experiencing an identical wildfire exposure. There is strong evidence, they concluded, that these effects are due to state and local building code changes – first after the deadly 1991 Oakland Firestorm, and again with the strengthening of  wildfire codes in 2008. The observed vintage effects are highly nonlinear, appearing immediately for homes built after building code changes. There are no similar effects in areas of California not subject to these codes or in other states that lack wildfire codes.

Their findings are similar to those in a paper published October 4, 2021 in which researchers analyzed the structures that were destroyed and those that survived the Camp Fire that ran through the city of Paradise, California in 2018. They considered at least four primary characteristics of structures:

  • Were they built before or after the adoption in 2008 of Chapter 7A of the California Building Code.
  • Distance to nearest destroyed structure.
  • Number of structures destroyed within 100 meters.
  • Pre-fire overstory tree canopy within 100 meters

They found that the last three criteria were the strongest predictors of survival. Homes more than 18 meters (59 feet) from a destroyed structure and with less than 53 percent pre-fire overstory canopy within 30 to 100 meters (98 to 328 feet) survived at a substantially higher rate than homes in closer proximity to a destroyed structure or in areas with higher pre-fire overstory canopy. Most fire damage to surviving homes appeared to result from radiant heat from nearby burning structures or flame impingement from the ignition of near-home combustible materials. The researchers concluded that building and vegetation modifications are possible that would substantially improve outcomes. Among those include improvements to windows and siding in closest proximity to neighboring structures, treatment of wildland fuels, and eliminating near-home combustibles, especially within 1.5 meters of the structure.

(The video below was shot December 31, 2021, the day after the Marshall Fire destroyed more than 1,000 homes in Boulder County, Colorado. Notice that most of the surviving homes seen in the video had fewer homes in close proximity.)

The authors noted that while Chapter 7a includes requirements not found in many building codes, a few other codes are more complete incorporating multiple construction classes based on anticipated radiant heat, flame, and ember exposure levels. For example Chapter 7A does not consider the interaction between components such as siding, window, and the under-eave area on an exterior wall.

California is embarking on a pilot project in which owners of vulnerable homes in lower income neighborhoods will be given grants up to $40,000 to retrofit the structures, making them more resistant to wildfires.

Home Ignition Zone

This data helps to illustrate that the condition and characteristics of the Home Ignition Zone should be an extremely high priority in preventing structures from burning as a wildfire approaches.

There is an opportunity for much needed improvement in both current building codes and how we live in wildfire prone WUI areas.

Thanks and a tip of the hat go out to Gerald.

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Author: Bill Gabbert

After working full time in wildland fire for 33 years, he continues to learn, and strives to be a Student of Fire.

10 thoughts on “Data shows building codes can reduce vulnerability of homes in wildfires”

  1. Thank you for this great article, which touches all the important aspects of wildfire resilience!
    I apologize for the self-advertisement, but what about building houses that do not burn?
    Climate change is no longer a future threat: it is here and it is already changing everybody’s life. It is too late to address it by small improvements around the edges. We need to think outside the box.
    A comment I hear very often is that it is too expensive or impractical to build houses that are fire-proof. I strongly disagree with this view: it is possible to build affordable, sustainable, and safe houses for everybody. Earthen construction is one of the possible tools to achieve this goal. Yes, there are challenges, but the technical challenges can be resolved through research efforts. We need to have the will to overcome the other challenges (social, cultural, etc.). Soon, we will be obliged to; hopefully, we will before the social costs become unbearable.

  2. The issue is distance from heat source. Build them close together (5 feet from property lot side lines) and radiant heat becomes the driving factor. Small lots with big homes has become the norm today, regardless of whether its Metropolitan or rural. Subdivisions, tracts, whatever name they go by, we pack them like sardines to maximize profit without regard to safety in this instance. Space is what is needed between structures when these types of fires start. That is the simplest fix out there.

  3. Casually looking at several rural fire stations in El Dorado county, California suggests a public awareness campaign of establishing and maintaining fire wise landscaping around existing fire stations, then posting a sign telling about the project with initial costs and annual maintenance might help get the public on board. If nothing else, perhaps fewer fire stations would be destroyed in the inevitable fires we are suffering. As it is, homeowners are probably saying to themselves “if the fire department can’t be bothered to establish firewise landscaping, why should I”.

  4. While we often think we are coming up with new solutions to new problems, we must remember that during the Gold Rush era towns were completely burning with regularity and lives were being lost. Ordinances were past where brick buildings, iron shutters placed on windows and other requirements were required. Here is a an article that looks back.

    Regulating ignition sources was also recognized as a solution to prevent fires. Here is an article I wrote that speaks about how “Railroads Can Teach Utilities How to Stop Causing Fires”

    We need to design our buildings and our utilities for the environment they are located in whether the threat is fire, flood, earthquake or security.

  5. I was on a WUI mitigation task force in the ’90s on the Colorado Front Range that came up with recommendations including zoning, building codes, roads and more. The commissioners under pressure from builders and realtors only adopted roofing standards. Nothing else. The “property rights” crowd was vocal with their “you can’t make me” baloney. Since then we’ve had the Crystal Fire, High Park Fire, and Cameron Peak. Still no action.

    1. The ideals of property rights and profiteering over community safety seem to be really deeply ingrained in the US and especially in the Intermountain West, which seems to tend more libertarian. It would be great to see some federal policy that mandated building codes in areas at high fire risk rather than piece-meal policy at the state and local level. That is almost certainly wishful thinking though.

  6. I did research on firesafe landscaping for the Mayors Firestorm Taskforce, after the Oakland Hills Fire, then watched houses, with new trees planted right next to them, go up on those burned lots. So, if the Hills burn again, the building code improvements may be offset by the canopy.
    I am a writer, not a Fire professional, but I have tried to talk to homeowners about trees and brush, and it’s as hard as talking about politics and religion. And, while building inspectors have power, who is going to stop people from planting trees?

  7. This is indeed a conundrum, born of an ever-increasing population. It’s all about money/profit. The 1973 song, “Money” by Pink Floyd comes to mind. More stringent building codes place a burden on lower and middle class people. Building codes need not be more stringent necessarily. It just comes down to profits. Density of homes seems to be the real issue. In most cases I suspect a less densely packed subdivision is going to be more “prestigious” hence worthy of higher-priced homes. There must be proprietary density formulae that developers/investors rely upon to eek out the most “legitimate profit”. Considering the increase in tax base some responsibility surely falls upon the entities that ultimately approve a subdivision. Money, it’s a gas but keep your hands off my stack!.

  8. When planning a subdivision, those in the building trades press for the most lots they can get out of any plat of dirt. The Realtors do the same, and like those in the trades they press for the biggest structures that can be built on any parcel. Therein lie your problems. The pressure to maximize dollars for the builders and realtors is phenomenal. The person who owned the dirt for the last 50 years doesn’t realize much difference; if that person put CC&R’s that limited structure size and placed minimums on lot sizes the realtors, lawyers, and builders would howl like they were being killed. But they would still buy, and they would make a good living. They would create and present for market a much more survivable, sustainable, happier community.

    But first, you must first get past that initial screeching howl.

    I went through this process a few years ago. I wish like anything I had stuck to my guns and presented a better planned community for those who must come behind us.

  9. Building clusters are just like trees/shrubs/grass; they can be categorizes into fuel types.
    If we consider how Ponderosa pine is different compared to Black spruce which is different than trembling aspen, we can create “urban fuel types”.
    When creating our wildland fuel types we use things like species flammability, horizontal/vertical arrangement, horizontal/vertical continuity, and understory composition.
    Obviously this is not rocket science. Folks in both the wildland and structural firefighting spheres have been saying this for decades.
    The problem is money, or lack thereof; it speaks louder and has the ear of every politician. Homeowners are also well aware of the conundrum presented by spending a large portion of their budget to address something that may not happen. Or may not happen in their time perspective.
    The cost of fire-proofing every home in the west is just like tornado-proofing every home in Kansas. Sometimes we play the odds.


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