Introduction
Hempcrete—a sustainable, carbon-sequestering building material—has officially arrived in Minnesota’s residential construction code. With the state’s adoption of IRC Appendix BL in 2025, Minnesota positions itself at the forefront of green building innovation in the U.S. If you’re a builder, architect, code official, or permit applicant, this move means new opportunities—along with a slate of updated permitting, inspection, and documentation requirements. This article details what Minnesota’s adoption of Appendix BL means for hempcrete project permitting, how requirements are evolving, and how project teams can successfully navigate the new landscape.
The Backdrop: IRC Appendix BL and Minnesota’s Early Adoption
The 2024 International Residential Code (IRC) introduced Appendix BL, which formalizes code pathways for hemp-lime (hempcrete) construction in one- and two-family dwellings. In spring 2025, Minnesota’s Technical Advisory Group (TAG) and the Construction Codes Advisory Council approved this appendix for the state’s next residential code cycle. This makes Minnesota one of the first states to recognize hempcrete assemblies for mainstream residential use [source].
By integrating Appendix BL, Minnesota enables non-structural hemp-lime wall assemblies—with strict guidance on mixes, fire safety, detailing, and testing—into the code. The new appendix covers not only traditional cast-in-place walls but also pre-fabricated hemp-lime panels, subject to compliance with other applicable codes.
Key Requirements Under IRC Appendix BL in Minnesota
Material Specifications
- Hempcrete Walls: Prescriptive mixes (hemp hurd, binder, water) meeting durability and fire standards
- Documentation: Project teams must provide manufacturer material data sheets, batch mix specifications, and supporting laboratory tests
- Fire Testing: Assembly performance must meet 1-hour fire resistance ratings, as validated by certified third-party labs once these assemblies are adopted into the 2027 IRC (tests already being piloted in MN in 2025)
Design & Engineering
- Nonstructural Use: Hemp-lime is permitted for non-load-bearing infill under Appendix BL. Structural members must comply with the IRC or an engineered design stamped by a Minnesota-licensed professional.
- Engineering Stamps: Stamped drawings are required when hemp-lime is used outside of prescriptive details, where buildings exceed two stories, or where local officials request additional analysis (e.g., seismic or unique assemblies).
- Thermal and Moisture Detailing: Projects must specify moisture management, vapor control layers, and surface finishes per BL104 to reduce risk of mold or wall degradation.
Construction Detailing
- Water-Resistive Barriers: Required at wall openings and peneterations, as per BL103.7.4 and BL104.5.1.
- Surface Finishes: Both interior and exterior hempcrete surfaces must receive appropriate coatings, lime plasters, or compatible siding to comply with BL104 and Minnesota’s climate zone challenges.
Permitting Pathway for Hempcrete in Minnesota
Required Submittals
- Plans and Elevations: Standard IRC drawing sets with explicit documentation of hemp-lime wall sections.
- Material Documentation:
- Material data sheets for hemp hurd and binder
- Mix design specs with site-specific adjustments
- Third-party fire and thermal test reports (ASTM E119 or equivalent)
- Engineering: Stamped details if outside prescriptive path.
- Moisture and Air Barrier Strategy: Explicit detailing of vapor, air, and water control layers, with manufacturer compatibility.
Plan Review Tips
- Highlight BL Compliance: Reference specific BL sections on construction drawings.
- Clarify Fire Ratings: Attach current MN pilot fire resistance test summaries and planned certification pathways.
- Moisture Controls: Detail strategies to ensure code officials’ confidence in performance.
Inspection Touchpoints and RFI Avoidance
Key Inspections
- Wall Assembly: Confirm proper mixing, depth, compaction, and alignment with approved plans.
- Curing and Weather Protection: Inspect site protection during hemp-lime curing, as premature moisture exposure risks wall integrity.
- Blower Door Test: Required per MN energy code (2024 update); ensure the hempcrete envelope achieves the mandated air changes/hour at -50 Pascals. Early pilots show typical prescriptive hempcrete walls are tight enough for code if vapor barriers are installed correctly [source].
- Vapor and Water Barrier Application: Inspect prior to finishes for continuity and adherence to submittal details.
Tips From Early Minnesota Projects
- Pilot teams recommend involving the building inspector early—bring sample mix, fire and thermal test data, and wall mock-ups to preconstruction meetings.
- Avoid redesigns: Over-document mix specs, and confirm vapor barriers with a building envelope consultant before final submittal.
- Document curing schedule and weather protection plans, so inspectors are reassured about wall performance, especially during spring and fall builds.
Navigating Energy Code—Blower Door & Vapor Control
With Minnesota enforcing rigorous energy codes—including the 3 air changes/hour blower door test—hempcrete builders must pay close attention to:
- Continuous Vapor Barriers: Hemp-lime is vapor-permeable, so integrate Class II/III vapor retarders as appropriate and show complete transitions at joints, window openings, and roofs.
- Joint Detailing: Intersections with traditional framing require enhanced sealant or gasket solutions to pass MN air-leakage tests.
- Testing: Pre-test with an envelope consultant before final inspection can save costly change orders.
Licensing, Enforcement, and Futureproofing
- Licensing: Residential contractors working with hempcrete must be properly licensed in Minnesota (check MN DLI guidelines for up-to-date requirements: https://dli.mn.gov/).
- City Adoption: Some cities may adopt additional clarifying requirements or issue bulletins as more hempcrete projects move forward in 2026. Stay in touch with your local building department for supplemental checklists.
- Anticipate Changes: Expect further code amendments as hempcrete gains field data for additional assemblies (precast panels, floor systems); the 2027 IRC is likely to refine fire and structural criteria based on Minnesota's pilot outcomes.
Key Takeaways for Builders, Designers, and Inspectors
- Start Early: Engage the local code official and request a pre-application meeting to reduce RFI cycles and unexpected delays.
- Over-Document: Provide thorough mix, thermal, and fire test details—most reviewers are new to hemp-lime, and comprehensive documentation accelerates approvals.
- Moisture Matters: Demonstrate a robust vapor and moisture control strategy. The most common RFI in early MN pilot projects related to vague or incomplete vapor barrier specs.
- Blower Door Success: Coordinate early on with energy consultants to ensure your hemp-lime assemblies can pass Minnesota’s stringent airtightness requirements.
- Code Evolution: The current code will continue to evolve—track MN DLI and your city’s bulletins for clarifications as more data emerges.
Additional Resources
Minnesota’s forward-thinking code adoption is accelerating the shift to sustainable construction across the Midwest. For businesses and specifiers, it’s time to skill up on new requirements, invest in airtight documentation, and educate team members and code officials alike.
For expert insights, compliance checklists, and live state-by-state regulatory updates on hempcrete and cannabis-connected building materials, rely on CannabisRegulations.ai to keep every project on track.
