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Q&A Spotlight

Building in a Wildfire Zone

An owner/builder in California looks for the safest exterior building materials

Despite efforts to limit the risk of wildfire, thousands of homes have been lost and hundreds have died in recent years. The best approach in some areas may be limiting development, halting new construction, or moving communities altogether. This scene is in the Coffey Park neighborhood of Santa Rosa, California, following fires in 2017. Photo courtesy California National Guard / CC.

GBA reader “Mojave Disaster” is asking a question that many others in the far West are confronting these days: Which building materials offer the greatest protection against wildfires?

In a post originally published nearly two years ago and updated just recently, Mojave writes, “As you may have heard, there have been some fires of greater speed and intensity than normal going on lately.” Unfortunately, the same words could have been written just this year, as residents of California, Washington, and Oregon coped with an onslaught of wildfires. Some problems just don’t go away.

Mojave is getting ready to build a superinsulated home with double-stud exterior walls. “What inexpensive, time-tested materials, and how thick, must I put to the exterior to have any chance of the house surviving the heat of a fire tornado?” Mojave asks. “Since there’s also the issue of soil liquefaction in this seismic zone, I hope the answer isn’t a massively thick concrete bunker.”

Windows and doors are another issue. Is there anything available in big-box outlets that would work?

Those are the questions for this Q&A Spotlight.

Use inert materials

Let concrete and steel be your friends, suggests Peter L.

“Exposed exterior wood is not a good idea,” he adds. “My recommendations would be an ICF [insulated concrete form] home with 6-in. concrete and rebar, and then use synthetic, non-flammable stucco like StuccoMax for the exterior walls.”

A steel roof also would help, as would paying very close attention to any venting details so that burning embers can’t get into the building.

Finally, Peter says, create a “defensible space” around the building that is free of trees and shrubs that could become fuel for an approaching fire. This vegetation-free zone should extend 30 to 50 ft. from the building.

“The above will…

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  1. Goodmanheat | | #1

    They already make a building material that will withstand a wildfire. It's called aerated autoclaved concrete. Used extensively for walls, floors and roofs in Europe. If building with wood I would use exterior insulation "mineral wool" 2" to 4" thick with stucco and a metal roof which is a common energy retrofit in Europe.

    1. daDIY | | #3

      That’s pretty much the conclusion I’ve reached also here in Southern California. But the devil is in the details. None of this is clearly in code yet, so it’s all a custom job. Even then, it will be hard finding competent contractors initially since it’s a new area. And seismic concerns will certainly have the local AHJs wanting engineer stamped plans since it’s not in code.
      One plus of stucco is that it can be imprinted to look like other materials and stained. Personally I dislike rough or dash exterior retrofits.

  2. derekisastro | | #2

    Why the specifics of using synthetic stucco's instead of using 'normal' stucco for the siding? What is the advantage? I assumed that even 'normal' stucco was fire resistant/proof?

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