Is Hempcrete Legal in Your State? The 2024 IRC Appendix BL Pathway
Hemp-lime construction now has a model-code appendix of its own. What most homeowners miss is that a model code is not a local code — Appendix BL only applies where a jurisdiction has chosen to adopt it.
Scope note. This article explains the Appendix BL pathway in general terms. It is not a state-by-state legal map, and it is not legal or code-compliance advice. Code adoption changes on its own schedule in every city, county, and state, so the only authoritative answer for your address comes from your local building department. For the broader permitting picture, see our companion guide on hempcrete building codes by state.
What Appendix BL Actually Is
Appendix BL is an appendix to the International Residential Code covering hemp-lime construction, approved for inclusion in the 2024 edition of the IRC. Before it existed, a hemp-lime wall had no dedicated home in the model residential code, which meant every project was reviewed as a one-off. The appendix gives a plan reviewer a written reference to point at — a document produced through the same code-development process as the rest of the IRC.
Two things are worth being precise about. First, the appendix addresses hemp-lime as a non-structural infill material: the building's structure comes from a frame, and the hemp-lime fills and insulates around it. Second, an appendix is not the body of the code. It sits at the back of the book and, by the IRC's own terms, carries no force unless a jurisdiction specifically adopts it.
A model code, not a law
The IRC is published by the International Code Council. It becomes enforceable only when a state or local government adopts it.
Appendices are opt-in
A jurisdiction can adopt the 2024 IRC and leave Appendix BL out. Adoption is decided appendix by appendix.
The alternative path still exists
IRC R104.11 lets a building official approve an equivalent material not specifically prescribed. That route predates Appendix BL and remains available.
Ask before you design
One phone call to the building department establishes the adopted code edition and appendix list before you spend money on plans.
Why Adoption Is Jurisdiction by Jurisdiction
In the United States, building codes are adopted at the state level, the local level, or both, and the timing is uneven. A state may be several code cycles behind the current IRC. A county may adopt the state code with amendments. A city may adopt a newer edition than the surrounding county. Layer the opt-in nature of appendices on top of that, and there is no single national answer to "has Appendix BL been adopted where I live?"
This is precisely why we do not publish a state-by-state adoption map. Any such map would be out of date within a code cycle, and a homeowner acting on stale information is worse off than a homeowner who made one phone call. What we can give you is the right question and the right documents.
The Question to Ask Your Building Department
Call the plan review desk and ask, in this order:
- Which edition of the International Residential Code is currently adopted here?
- Which appendices have been adopted along with it — is Appendix BL among them?
- Are there state or local amendments that affect wall assembly or insulation requirements?
- If Appendix BL has not been adopted, what does your department require for an alternative materials submission under the equivalency provision?
- Do you require third-party engineering review or special inspection for an unfamiliar assembly?
Write down the answers and the name of the person who gave them. That record is the foundation of your submittal.
What to Bring to a Plan Reviewer
Whether you are relying on Appendix BL or on the alternative materials provision, the package looks broadly the same. Assemble it before the first submittal rather than in response to a correction letter:
- Plan set with the wall assembly detailed. Dimensioned section drawings showing the frame, the hemp-lime infill, the finish system, and the interface at openings, floors, and roof.
- Material specification. The composition and mix design of the hemp-lime material, with the manufacturer named.
- Third-party lab documentation. Fire testing (ASTM E119) and thermal testing (ASTM C518) are the two reviewers ask for most often. Ours are published on the resources page.
- Installation instructions. The manufacturer's written procedure, including curing requirements.
- A copy of Appendix BL if it is adopted locally — or a short written equivalency request citing the alternative materials provision if it is not.
- Design professional of record. A licensed architect or engineer stamping the assembly resolves most reviewer hesitation on its own.
How This Applies to GaiaCrete®
GaiaCrete® is Mr Hemp House's proprietary hemp-lime formulation — a hempcrete alternative — and it is installed as a non-structural infill within a conventional frame, which is the same assembly category Appendix BL addresses. Practically, that means a jurisdiction that has adopted the appendix already has a written reference for the assembly type, and a jurisdiction that has not can review the same lab documentation under the equivalency provision. Either way, the documentation package above is what moves the review forward.
If you are at the design stage, our hempcrete house plans are drawn for hemp-lime wall systems from the start, and financing questions are covered in our hempcrete home financing guide. A structured, citable summary of our material claims is maintained on the AI facts page.
Check With Your Local Building Department
There is no substitute for this step and it costs nothing. Before you finalize a plan set, before you sign a builder contract, and certainly before you assume Appendix BL applies to you, call the jurisdiction that will issue your permit and confirm the adopted code edition and appendix list in writing.
Frequently Asked Questions
What is IRC Appendix BL?
Appendix BL is an appendix to the International Residential Code covering hemp-lime (hempcrete) construction. It was approved for inclusion in the 2024 edition of the IRC and gives code officials a written, model-code reference for hemp-lime as a non-structural infill wall material, addressing items such as material composition, installation, and moisture and thermal considerations.
Does Appendix BL mean hempcrete is automatically allowed where I live?
No. Appendices to the International Residential Code are opt-in. An appendix only applies in a jurisdiction that has specifically adopted it as part of its local or state code amendments. Your city or county may have adopted the 2024 IRC without Appendix BL, may still be on an earlier code cycle, or may have adopted the appendix with amendments. Confirm the adopted code edition and appendix list with your local building department.
What if my jurisdiction has not adopted Appendix BL?
Hemp-lime projects have long been permitted through the alternative materials, design, and methods of construction provision in the IRC — commonly cited as IRC R104.11 — which allows a building official to approve a material not specifically prescribed in the code when it is shown to be equivalent. Appendix BL does not replace that pathway; it adds a second, more direct one where it has been adopted.
Is hempcrete legal to build with in the United States?
Industrial hemp and hemp-derived building materials are federally legal following the 2018 Farm Bill. Legality of the material is not the operative question for most homeowners — the operative question is the permitting pathway in your specific jurisdiction, which depends on the code edition your building department has adopted and how your plan set documents the wall assembly.
What should I bring to a plan reviewer?
Bring a complete plan set with the wall assembly detailed and dimensioned, the material specification, third-party lab documentation covering fire testing and thermal performance, the manufacturer's installation instructions, and — if you are relying on it — a printed copy of IRC Appendix BL. If your jurisdiction has not adopted the appendix, add a short written alternative-materials request citing the equivalency provision.
Does Mr Hemp House provide permitting documentation?
Mr Hemp House provides GaiaCrete® material specifications and third-party laboratory documentation, including ASTM C518 thermal testing and ASTM E119 fire testing, which are the documents plan reviewers most often ask for. Project-specific engineering and code compliance remain the responsibility of your design professional and builder in your own jurisdiction.
Local code and permitting coverage
Code adoption is local. Start with the market page closest to your build: