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A Multi-Decade Journey to Legitimacy
For decades, hemp was effectively banned from American construction — not because of any failing of the material itself, but simply because industrial hemp itself was illegal. While hemp-lime construction had been thriving in Europe for decades, the U.S. couldn't integrate these techniques into building codes because the plant couldn't be legally grown.
That all changed with the 2018 Farm Bill, which legalized industrial hemp as a commercial crop. This legislative shift opened the door for what would become a multi-year campaign to bring hemp construction into the American building code mainstream.
The Breakthrough: 2022
The pivotal moment came in September 2022, during a public hearing in Louisville, Kentucky, overseen by the International Code Council (ICC). At that hearing, hempcrete was officially approved for inclusion in the U.S. model residential building code.
The ICC's committee determined that hemp-lime construction was "another technology similar to that of straw bale and cob wall construction" — a comparison that validated its place alongside other established natural building methods. The approval applied to hempcrete as a non-structural wall infill system for one- and two-family dwellings and townhouses.
"We have done something that they said could not be done!"
— Jacob Waddell, then executive director of the US Hemp Building Foundation, now founder of the Hemp Building InstituteThe 2024 International Residential Code: Appendix BL
The 2022 approval paved the way for the formal inclusion of hemp-lime in the 2024 International Residential Code (IRC) as Appendix BL: Hemp-Lime (Hempcrete) Construction. The IRC serves as the basis for residential building codes in 49 out of 50 U.S. states.
What Appendix BL actually does
According to the official ICC language, Appendix BL "governs the use of hemp-lime as a nonstructural building material and wall infill system." Hemp-lime is defined as "a bio-aggregate composite consisting of hemp hurd and a lime-based binder," commonly referred to as hempcrete.
The appendix provides clear guidelines for:
- Material specifications and testing requirements
- Construction details for cast-in-place, spray-applied, and block systems
- Fire-resistance ratings for various wall assemblies (1-hour rated walls with specific framing configurations)
- Seismic requirements — engineered designs required for high-risk zones
⚠️ Key scope limitation
Appendix BL allows hemp-lime use in buildings up to two stories in low seismic risk regions prescriptively, without engineering. Regions of high seismic risk and taller buildings require an engineered design.
The Fire Testing That Made It Possible
The code approval didn't happen in a vacuum. It was backed by rigorous ASTM fire testing:
- ASTM E84-19B (surface burning characteristics) testing has been completed, measuring flame spread and smoke development. Hemp insulation has achieved flame-spread scores of zero on this test.
- ASTM E119 (fire resistance of building assemblies) testing has also been conducted. In July 2024, a spray-applied hempcrete wall was subjected to a 1,700°F heat test as part of ASTM E119 fire resistance testing.
The 2024 IRC Appendix BL explicitly references ASTM E119 and UL 263 for determining fire-resistance ratings. The appendix includes provisions for 1-hour fire-resistance rated hemp-lime walls with center stud framing (12-inch thick spray-applied hemp-lime) and exterior stud framing configurations.
Where Has It Been Adopted?
State-level adoption
TAG voted 8–1 in favor, July 2025
Minnesota is leading the charge as the first U.S. state on the path to adopting Appendix BL. The state's Technical Advisory Group voted 8–1 in favor of adopting hempcrete into the state residential code, with changes set to be finalized in the 2026 revision. When that happens, Minnesota will be the first state to officially authorize hemp in building construction.
The Lower Sioux Indian Community in Minnesota has been a pioneer, already building four hempcrete homes on their reservation using hemp grown and processed on-site. They received a nearly $5 million EPA grant in 2024 to renovate 30 homes with hempcrete.
Major city adoptions
First major U.S. city to fold Appendix BL into local law
Hemp-lime walls up to 20 feet tall can now be permitted like any standard 2×6 stud assembly. Before this adoption, hemp-lime projects in Austin waited up to six extra weeks for "alternate means" approvals, often requiring costly third-party engineering letters. Those letters are now optional.
Incorporated statewide, with city-level adoption
California has incorporated Appendix BL into its 2025 California Residential Code, with cities including San José, San Diego, and Los Angeles County adopting the provisions.
Appendix BL adopted
Among the early municipal adopters following the 2024 IRC publication.
The Road Ahead: Commercial Buildings and the IBC
While residential construction now has a clear path forward, commercial buildings are the next frontier. The International Building Code (IBC) — which governs commercial occupancies not covered by the IRC — has not yet adopted hemp-lime provisions.
Work began in 2024 to get hempcrete accepted as a standard infill insulation in large commercial projects under the IBC. The IBC is renewed every three years, and petitions were accepted in 2025 for the next code cycle.
The Team Behind the Achievement
This historic code recognition wasn't the work of a single organization — it was a multi-year, multi-million-dollar community effort.
The US Hemp Building Association (USHBA) and its foundation raised more than $50,000 to develop the appendix. The application was guided by a team of civil engineers, hemp-lime builders from Europe and the USA, architects, and code experts who had previously helped straw bale builders gain certification in the 2018 residential codes.
Key figures included Martin Hammer, David Eisenberg, and Anthony Dente — a trio of code consultants who spent decades shaping standards for straw bale, light straw clay, adobe, tiny homes, and now hemp-lime construction. Their quiet, consistent work led to a breakthrough: hemp-lime earned its place in the 2024 International Residential Code.
The full list of contributors reads like a who's who of natural building: Cameron McIntosh, Matt Marino, Chris Magwood, Tim Callahan, Mattie Mead, Tom Rossmassler, and many others.
What This Means for Builders and Homeowners
The inclusion of hemp-lime in the IRC represents a fundamental shift.
"The forward-thinking visionary/pioneers who went before to establish this code are owed a deep gratitude. This gratitude will be best expressed by our unified professional focus and efforts to educate and execute with excellence."
— Ray Kaderli, USHBA PresidentFor builders
- Clear, standardized guidelines for hemp-lime construction
- Streamlined permitting without "alternative material" red tape
- Reduced costs — no more expensive third-party engineering letters for standard applications
For homeowners
- Legal, approved access to healthier, non-toxic building materials
- Greater choice in how they build their homes
- Carbon-sequestering homes that lock away CO₂ for decades
What it means for HempShield
- A legal, approved product category. Appendix BL provides the regulatory foundation for hemp-lime construction nationwide.
- A rapidly expanding market. With Minnesota, Texas, California, and others adopting the code, the addressable market grows every month.
- The right moment to enter. The residential code is settled; commercial is next. Early movers will define the industry.
- Proven science. ASTM fire testing, carbon sequestration data, and decades of European experience all back the material's performance.
- A movement, not just a market. This is the culmination of decades of advocacy by some of the most dedicated professionals in sustainable construction.
The 2027 Update: Work Continues
The work isn't finished. The same team that secured the 2024 approval is now back at work updating Appendix BL for the 2027 IRC, adding fire-resistance data, refining mass wall language, and strengthening the technical foundation for the entire natural building community.
"This work is a community effort that will benefit the entire industry."
— Cameron McIntosh- 2018Farm Bill
Industrial hemp legalized as a commercial crop, making domestic hemp construction possible.
- September 2022ICC hearing, Louisville KY
Hempcrete approved for inclusion in the U.S. model residential building code.
- 2024IRC Appendix BL published
Hemp-lime formally enters the International Residential Code.
- July 2024ASTM E119 testing
Spray-applied hempcrete wall subjected to a 1,700°F heat test.
- July 2025Austin, TX adopts
First major U.S. city to fold Appendix BL into local law.
- 2025California, Telluride adopt
Appendix BL incorporated into the 2025 California Residential Code.
- 2026Minnesota finalizes
Expected to become the first state to officially authorize hemp in building construction.
- 2027IRC update in progress
Appendix BL revised with additional fire-resistance data and refined mass wall language.
Building under Appendix BL?
Send us your wall section, climate zone, and jurisdiction. We'll confirm whether your AHJ has adopted the appendix and come back with a spec'd package and lead time.
Get a Free ConsultationRead next: The Ultimate Guide to Hemp Insulation — cost, R-value, fire rating, installation, and comparisons to every alternative on the market.