In October 2017, wildfires ravaged much of North Bay, the subregion of the San Francisco Bay Area often referred to as “Wine Country.” Over a three-week period, 250 fires burned at least 245,000 acres of land, killed 44 civilians, and destroyed 8,900 buildings.
But there were a handful of homes within range of the fires that didn’t burn down.
On the first night of the fires, a blaze reached the roof of a home in Napa and destroyed everything in the house except its exterior walls.
Later in the month, another fire torched the formerly lush green lawn of a home north of Sonoma and charred a sliding wood door on the home’s exterior, but the home didn’t catch fire.
And flames scorched the exterior walls of another house, located between Napa and Sonoma, but didn’t get inside the house. Two neighboring houses were completely destroyed.
All of these homes had something in common: They were built by architects who insulated the exterior walls of the homes with bales of straw. The California Straw Builders Association (CASBA) cited their resilience during the North Bay Fires in a report that argues that straw bale walls have superior fire resistance to traditional construction materials.
Straw may not seem like an intuitive material for fire resistance, but it’s one that CASBA’s members have been testing for over 20 years. In a typical straw bale wall system, blocks of straw are stacked inside of the exterior walls of homes and held together with lime plaster. Unlike loose straw, which burns quickly, the lack of surface area inside of straw bales doesn’t allow oxygen to flow through it, which makes it burn slower. “It’s like trying to burn a phone book,” says Ken Haggard, an architect who builds with straw bale and has designed over 300 homes.
While most homes built today can only stand up to a standard fire resistance test for an hour, straw bale wall systems held together with lime plaster can last for up to two hours, according to tests performed in 2006 and 2011. The one-hour time difference might not seem that big, but it could be the difference between life or death for people stuck in the grip of a scorching wildfire and can help save their homes from being completely destroyed.
“It’s a substantially better wall,” David Arkin, an architect who builds homes with straw bale walls and co-director of CASBA, told OneZero. “And then when it’s combined with other fire safe measures such as heavy timber framing, and metal or some other fire-resistant roof it can create a fairly fire-resistant building.”
“Homes built with straw bale walls could provide refuge from fire for occupants unable to escape.”
Building materials that can stand up to fires may be more necessary than ever as wildfire seasons, the time when weather conditions are ripe for intense, fast-moving blazes, are becoming longer for much of the world. Historic, record-setting wildfires have burned millions of acres of land and driven thousands of people out of their homes globally — in the United States, in Australia, in India. And some researchers say that climate change will increase the likelihood of seeing more catastrophic wildfires in the future.
But this grim forecast has only increased interest in straw bale construction marginally, at least in California, according to several architects who work with the material. They say there are multiple reasons for this. One reason is that straw bale construction was only added to the International Residential Code, which regulates design and construction of most houses and townhouses, in 2015. Rebecca Tasker, co-owner of the natural-homebuilding firm Simple Construct, says she often has to point building code officials to the part of the building code that regulates straw bale construction. She also says the costs of using straw bale construction are generally higher than traditional construction materials.
Massey Burke, an architect who’s designed buildings in California, Pennsylvania, and Washington, D.C. and is the co-director of CASBA, says another reason is because “the culture of building is famous for changing really slowly.”
An example of this is drywall, which was invented in 1916, but didn’t start catching on as a popular building material until the 1940s. That building material had a major corporation behind it, United States Gypsum Corporation, which pushed it as a product. Burke says that’s lacking for straw bale.
But the most common reason straw bale builders gave for its slow adoption into the market is that most people don’t think of straw bale as a building material.
“It’s a leap that not a lot of people are able to take,” Arkin says. “Some of that we blame on the first little pig, who built the straw house.”
All of the straw bale home builders who spoke to OneZero are enthusiastic about the benefits of using the material — it can also sequester carbon from the atmosphere, is nontoxic when it decomposes, and helps reduce energy consumption — but all of them also said it’s not the silver bullet for making homes more fire-resistant. Still, they see how more widespread adoption of the construction material could benefit communities that will likely see more frequent and intense wildfires in the future.
“Wider use of straw bale construction could decrease the spread of wildfires from one home to the next,” Martin Hammer, an architect based in Berkeley and lead author of part of the IRC code on straw bale, told OneZero. “Homes built with straw bale walls could provide refuge from fire for occupants unable to escape.”