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Hempcrete Approved for U.S. Residential Building Codes

Hemp-lime, or hempcrete, achieves a milestone: U.S. residential code approval paves the way for greener, healthier homes nationwide.

By Medha deb

Created on Sep 26, 2025

Hemp-lime, or hempcrete, achieves a milestone: U.S. residential code approval paves the way for greener, healthier homes nationwide.

Hempcrete Achieves Approval in U.S. Residential Building Codes

In a landmark move for sustainable construction, hemp-lime, commonly known as hempcrete, has been officially included in the International Residential Code (IRC) for the United States. This monumental approval paves the way for more environmentally friendly homes, greater material innovation, and the mainstreaming of carbon-sequestering building techniques across the country. The move results from years of advocacy and research led by the U.S. Hemp Building Association (USHBA), architects, engineers, and natural building pioneers.

What is Hempcrete?

Hempcrete is a biocomposite building material made from the woody core of the hemp plant (hurds or shiv) blended with a lime-based binder. Unlike conventional concrete, hempcrete is non-structural and typically used as an insulating infill within a structural frame, contributing properties such as:

Exceptional thermal insulation, enhancing energy efficiency
Moisture regulation and breathability, minimizing the risk of mold
Natural fire resistance—hempcrete’s high lime content protects against fire spread
Low embodied carbon: it actually locks atmospheric CO₂ within the walls for the material’s lifespan
High acoustic absorption for quieter interiors
Pest and rot resistance

Hempcrete’s use in Europe stretches back decades, notably in France and the UK, where it has found success in eco-homes and renovations of historic structures. Despite these international precedents, stringent U.S. building codes long halted its official inclusion until now.

The Road to Hempcrete Approval

The path to hempcrete’s rigorous code acceptance highlights both the excitement around alternative materials and the complexities of American code culture:

Historic prohibition of industrial hemp in the U.S. made research and development difficult until hemp cultivation was federally legalized in 2018
Code inclusion efforts, spearheaded by the USHBA and its foundation, involved raising over $50,000, technical documentation, and committee collaboration with international experts
Years of lobbying, testing, and model homes demonstrated hempcrete’s safety, thermal performance, and ecological advantages
ICC (International Code Council) ultimately voted to approve hemp-lime as a prescriptive appendix for the 2024 IRC

What Does the Code Say?—Appendix BL

The International Residential Code (IRC) is America’s predominant model code for one- and two-family dwellings and townhouses, forming the basis for building regulations in 48 states (all except Wisconsin and Arkansas) and Washington, DC.

The new regulations are found in Appendix BL (Hemp-Lime or Hempcrete Construction) in the 2024 IRC. Key contents include:

Hempcrete is permitted as non-structural wall infill, meaning it provides insulation and enclosure but not structural support
Applicability: Appendices must be explicitly adopted by a state or local jurisdiction for enforcement. Many do not automatically include all IRC appendices
Height and risk limitations: Permitted prescriptively in buildings up to two stories in areas of low seismic risk; engineered design is required for higher-risk regions or taller/larger structures
Project-by-project proposals: Where the appendix is not adopted or the scope does not fit (for example, for commercial or multi-unit projects), builders can still propose hempcrete to local building officials on a case-by-case basis

Impact on States and Local Jurisdictions

Because the IRC and its appendices are model codes, adoption varies from state to state and sometimes municipality to municipality. Most U.S. states are currently reviewing or are in the process of adopting the 2024 IRC, which means the first wave of local approvals may roll out in 2024–2025. Projects outside of the IRC’s direct scope—like commercial or institutional buildings—currently fall under the International Building Code (IBC), with possible adoption of hempcrete into those codes expected in future cycles.

Why Hempcrete?—Environmental and Health Benefits

Hempcrete’s approval is a major step toward sustainable construction practices. Here are its widespread advantages:

Carbon sequestration: Hemp plants pull CO₂ from the atmosphere as they grow, and the finished hempcrete walls continue to capture and store some carbon while curing
Low toxicity and improved indoor air quality: Hemp-lime does not emit volatile organic compounds (VOCs) or other indoor pollutants
Resilience: Mold-resistant, pest-repelling, highly fire-resistant, and rot-resistant
Thermal comfort: Its insulation and thermal inertia help keep homes cool in summer and warm in winter while reducing energy use

Comparing Hempcrete and Traditional Building Materials

Feature	Hempcrete	Traditional Insulation/Concrete
Composition	Hemp shiv + lime binder	Petrochemicals/Portland cement
Carbon Footprint	Negative (stores carbon)	Positive (emits carbon)
Fire Resistance	High	Varies (fiberglass/masonry resist, foam burns)
Moisture Handling	Excellent, vapor-permeable, resists mold	Poor (in foam), may trap moisture/mold
Insulation Value (R-value)	Moderate, with high thermal inertia	Ranges from low (masonry) to high (spray foam)
Toxicity	Non-toxic	Can off-gas or contain hazardous materials
Longevity	Can exceed 100 years	Varies considerably by type

Hempcrete’s Limitations and Remaining Challenges

While hempcrete represents a significant opportunity, some challenges and limitations remain:

Not a structural material: Requires a timber or steel frame for primary support
Implementation depends on local code adoption and builder acceptance
Knowledge and familiarity are still limited among inspectors, architects, contractors, and developers in much of the U.S.
Industrial hemp supply chains are still maturing domestically, and scaling up U.S. hempcrete production will take time
Still awaiting approval for use in non-residential (commercial, institutional) contexts, expected in future International Building Code updates

How the Approval Was Achieved: Advocacy and Partnerships

This historic code update is due to the persistent efforts of a dedicated network across North America and Europe:

U.S. Hemp Building Association (USHBA): Coordinated the campaign, oversaw technical documentation, and spearheaded lobbying efforts
Civil engineers, architects, and hemp builders: Provided the scientific validation and field expertise to satisfy code committees
International precedents: Decades of safe and effective hemp-lime homes in Europe guided the framework for U.S. adoption
Supporters in Canada: Canadian builders, with over a decade of legal hemp construction experience, offered important research and testimony

Key individuals, such as Jacob Waddell (former USHBA executive director), Ray Kaderli (USHBA president), and Martin Hammer (natural building architect), played vital roles in the process.

What’s Next for Hempcrete in America?

With code approval in place, the coming years are set to witness key changes in the construction landscape:

Increased adoption as states and cities update their building codes to reflect the IRC 2024 edition, including Appendix BL
Ongoing education campaigns targeting builders, code officials, and homeowners to improve comfort with the material
Strengthening domestic hemp supply chains, from U.S. hemp farms to processing and lime integration facilities
Anticipation of commercial and institutional code approval as the International Building Code undergoes its next cycle in the coming years
Innovative homeowners and progressive developers are likely to lead early adoption, especially in states eager for sustainable solutions

People Behind the Push: Experts and Advocates

Jacob Waddell: Former USHBA Executive Director and founder of the Hemp Building Institute, led key application and certification efforts
Ray Kaderli: USHBA President recognized the foundational work done by building code pioneers
Martin Hammer: Architect and code consultant, instrumental in drafting code language and supporting adoption strategies
Chris Magwood: Canadian natural builder, provided cautious optimism and perspective on practical implementation
Civil engineers, builders, and architects collaborated both in the U.S. and abroad, sharing lessons learned and technical research

Frequently Asked Questions (FAQ)

Q: What is hempcrete’s role in a home?

A: Hempcrete is used as a non-structural, insulating wall infill within a framed structure. It surrounds the frame to provide insulation, vapor regulation, and fire protection.

Q: Is hempcrete now legal across the U.S.?

A: Hempcrete is now approved in the 2024 International Residential Code, but each state and municipality must explicitly adopt Appendix BL for enforcement. Builders can also propose its use directly to officials, even in areas where it hasn’t yet been adopted.

Q: Does hempcrete replace concrete?

A: No, hempcrete does not replace structural concrete. While it resembles concrete in appearance, it serves solely as insulation and enclosure—not for load-bearing walls, foundations, or structural supports.

Q: What are hempcrete’s green credentials?

A: Hempcrete is carbon negative, locking atmospheric CO₂ into the wall system, and its production requires less energy and emits fewer toxins than conventional insulation or concrete. Its breathability also helps improve indoor air quality.

Q: Can hempcrete be used in commercial buildings?

A: Not yet under the current code—only residential use is approved through the IRC. Commercial inclusion in the International Building Code may come in future cycles.