California homeowners are facing a crisis. Wildfires are increasing in frequency and intensity, and the reliance on conventional, often toxic, building materials is exacerbating the problem. These materials not only fuel the flames but also leave behind a residue that contaminates the environment.
A coalition of natural building experts believes hemp-based construction offers a viable solution. They are actively petitioning state agencies to fast-track the adoption of natural building materials, including hemp-lime (also known as hempcrete), into the California Building Codes for 2025. These materials are already recognized in the 2024 International Residential Code.
Hemp-lime is a bio-composite material made from the hemp plant, lime, and water. It hardens into a stone-like substance with remarkable properties. Advocates say it offers superior fire resistance, regulates humidity, improves indoor air quality, and provides excellent thermal performance, potentially reducing energy costs.
“For a client looking to rebuild after a fire, hemp-lime is a smart choice,” says Aaron Grail, a natural builder based in Sebastopol, CA. “It’s not just about fire resistance, it’s about rebuilding in a way that prioritizes health, durability, and resilience. Hempcrete doesn’t burn; it chars and protects the structural frame.”
Currently, natural building materials can be approved on a case-by-case basis through the “Alternative Means and Methods” section of the California building code. However, advocates argue that statewide adoption is crucial to streamline the process and provide certainty for builders and homeowners.
Martin Hammer, a Berkeley-based architect and co-drafter of the hemp-lime appendix, emphasizes that without state adoption, the 2024 IRC appendices remain voluntary for local jurisdictions. The California Department of Housing and Community Development (HCD) declined to adopt the natural building appendices last June, though the Office of the State Fire Marshal (SFM) did approve part of the hemp-lime appendix as a non-combustible material.
The benefits of natural building materials are evident in the aftermath of wildfires. Straw bale homes with lime plaster, for example, have been shown to withstand fires that decimate surrounding structures built with conventional materials.
David Arkin, a Berkeley-based architect, has designed numerous natural homes that demonstrated fire resistance during the 2017 North Bay wildfires. One homeowner even sought refuge in their straw bale home as the fire raged, surviving unharmed while everything around the house was destroyed.
While challenges remain, proponents of hemp-based construction are optimistic. They point to increasing recognition from insurance underwriters, the rise of embodied carbon accounting, and growing awareness among homeowners and developers as positive signs.
Lisa Sundberg, founder of the Indigenous Habitat Institute, believes the time is right for hempcrete panel manufacturing. Her organization recently secured approval for a permitted hempcrete ADU in Eureka, CA. “Catastrophic wildfires keep happening in California, followed by skyrocketing housing insurance,” Sundberg says. “Hempcrete is a powerful contender as a carbon-negative building material moving forward.”
As California grapples with the increasing threat of wildfires and the need for sustainable building solutions, hemp-lime and other natural materials are gaining traction as a viable path forward.
