People Are Future-Proofing Their Homes With… Straw

Straw bale wall systems stand up to fire twice as long than those built with standard materials

This house was built with straw bale walls, which is more fire resistant than the construction materials used for most modern homes. Photo courtesy of Arkin Tilt Architects

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.

Flames reached the walls of this Northern California home during historic wildfires in the region in 2017, but didn’t enter the home because the exterior walls were insulated with straw bale. Photo courtesy of Michel Couvreax / Transmineral

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…