Hempcrete Just Became Legal Everywhere in America and Nobody in Real Estate Has Noticed

A carbon-negative, fire-rated wall system with a century of sequestration just entered the US building code, and the market has barely registered it.

Landlord Ledger Publications • Market • 2026-05-20

For thirty years, the French have been building with a material that sequesters carbon, passes fire tests, repels pests, regulates humidity, and gets stronger over time. The English have been using it too, and the Canadians. The wall assembly is called hempcrete: a biocomposite of hemp hurd (the woody inner stalk, also called shiv) bound with a lime-water slurry that cures slowly, mineralizing around the fibers and pulling CO2 from the atmosphere for decades. The material has been legal to grow in France since the 1980s. In the United States, it was illegal to grow industrial hemp at all until the 2018 Farm Bill changed that. And the building code recognition that professional architects need to specify a material? That arrived in the 2024 International Residential Code, as Appendix BL. The real estate industry has not caught up.

The Regulatory Gate Nobody Wrote About

Appendix BL, formally titled Hemp-Lime (Hempcrete) Construction, was the culmination of a multiyear campaign by the US Hemp Building Foundation, led by former executive director Jacob Waddell, who raised more than $50,000 and assembled a committee of civil engineers, European hemp-lime builders, architects, and code consultants. The proposal was approved unanimously through the International Code Council process. The 2024 IRC now constitutes the model residential code for 48 of 50 US states.

What the appendix provides is prescriptive language: a clear pathway for architects and plan reviewers who previously had to navigate the slow and expensive alternative materials approval process. Before Appendix BL, a hempcrete project required convincing a local building official, case by case, that an unfamiliar material was acceptable. That friction was the main reason hempcrete stayed a specialty practice despite decades of European precedent. "Code induction of a natural building material of any type is really big news," said Anthony Dente, a structural engineer at Verdant Structural Engineers in Berkeley, who submitted engineering data for the proposal.

The appendix allows prescriptive use of hemp-lime in buildings up to two stories, without additional engineering, in low seismic risk regions. It covers one- and two-family dwellings and townhouses. The appendices are opt-in by states and jurisdictions, but even unadopted, the code language gives builders a documented basis to propose use to local officials. The first US jurisdiction to formally adopt Appendix BL was the City of Austin, Texas, in April 2025, effective July 10, 2025. Minnesota followed. More jurisdictions are cycling through the three-year code adoption process.

The AIA Austin chapter, representing nearly 1,500 member architects, submitted a formal letter of support before the Austin vote. Policy strategist John Lawler wrote to city council that hempcrete "reflects the kind of city we want to be," noting it could "support local farmers and businesses." The vote was unanimous.

What the Material Actually Does

Hempcrete is not structural. This is the first thing architects tell clients and the first thing developers dismiss it for. But the structural constraint defines its actual market, and that market is enormous. Hempcrete functions as a non-load-bearing infill system: it goes around the structural frame (typically wood or steel), filling the wall cavity and serving simultaneously as insulation, vapor regulation, fire resistance, and cladding substrate. In that role, it competes with fiberglass batt, mineral wool, spray foam, rigid foam boards, sheathing panels, and interior wall finishes, all at once.

The performance specifications are striking. In 2025, builder Cameron McIntosh of Americhanvre facilitated ASTM E119 fire tests on three hemp-lime wall assemblies at Intertek Laboratories in York, Pennsylvania. All three passed one-hour fire ratings, including the hose-stream test, a result that earned unanimous approval from the IRC committee at its Cleveland code hearing. In fire-prone regions where exterior walls must achieve one-hour ratings, these numbers matter directly. Hempitecture confirmed in March 2025 that its hemp-lime formula passed ASTM E84 with a Class A rating, the highest fire classification, making hempcrete compliant with surface burning characteristics tests used by code officials nationwide.

Then there is the carbon story, which makes hempcrete categorically different from any other insulation material available. One hectare of industrial hemp sequesters approximately 15 tonnes of CO2 during the growing cycle alone. The lime binder, once installed, undergoes a long-term carbonation process: calcium hydroxide reacts with atmospheric CO2 and hardens into calcium carbonate, literally turning CO2 into stone inside the wall. This process continues for up to 100 years after installation. Each tonne of lime-based hempcrete is estimated to absorb and sequester roughly 249 kilograms of CO2 over its lifecycle. Life cycle assessments published in peer-reviewed journals have found that hempcrete formulations can achieve total lifecycle CO2 emissions of negative 16 kilograms per functional unit, making the assembly genuinely carbon-negative rather than merely low-carbon.

The additional performance properties are well-documented: thermal mass that moderates temperature swings, vapor permeability that prevents mold (the lime is naturally antifungal), pest resistance, acoustic dampening, and structural weight roughly one-eighth that of conventional concrete. Builder David Hall and architect Keith Moskow at Hillside Center for Sustainable Living in Newburyport, Massachusetts, used hempcrete tip-up panels to achieve passive house airtightness numbers their certifier described as the best he had seen in his career. Hillside is now the largest multi-unit hempcrete structure in North America, with 12 duplex units completed in early 2025 and a 48-unit total community planned.

The Supply Chain That Still Has to Catch Up

The code recognition is real. The market formation is not. The gap between those two conditions is where the investment story lives.

The central bottleneck is decortication. Hemp hurds must be separated from the plant's bast fiber by industrial processing. Most US decortication facilities can process only about five tonnes of hemp per hour, far below what commercial-scale hempcrete demand would require. The woody hurds are lightweight and bulky, making long-distance transport economically impractical. The implication is regional: hempcrete supply chains need to be local, with decortication and panel manufacturing within roughly 50 miles of the grow site.

In November 2024, the Department of Energy awarded Hempitecture an $8.42 million grant to construct a large-scale hemp fiber processing and manufacturing facility in northeast Tennessee. Americhanvre Cast Hemp in Pennsylvania received a $1.9 million federal grant in 2024 to expand its operations. The US EPA committed approximately $6.2 million to a hempcrete-focused nonprofit in July 2024. These are early moves in a capital build-out that the material's eventual scale will require.

Hempitecture, the market leader with over 6.5% market share, has been growing rapidly: HempWool insulation sales grew 50% year-over-year in 2023 and 200% year-over-year in 2024. CEO Mattie Mead projects $3 to $3.5 million in total 2025 revenue. The global hempcrete market was valued at approximately $570 million in 2024 and is forecast to grow at 14.9% annually through 2034, reaching $2.24 billion. The US market alone was valued at $169 million in 2024, growing at a 14.1% CAGR.

The training gap compounds the supply gap. Hempcrete installation requires different skills than conventional framing or insulation. Cast-in-place application uses slip-form techniques borrowed from European practice. Prefabricated panel systems, which are becoming the preferred approach for commercial projects, need fabrication yards and specialized lifting equipment. There are not yet enough trained installers in the US to service rapidly scaling demand. "To be commercially viable at scale, costs need to align more closely with conventional materials," one industry expert noted. That alignment depends entirely on supply chain maturation.

The Structural Frontier: zero-frm and the Load-Bearing Question

The constraint hempcrete cannot address is structural. It cannot replace foundation concrete, bearing walls, or structural columns. For developers building wood-framed houses, that is not a problem. But for commercial construction above two stories and anything relying on concrete structure, the question is more complex.

That is where okom wrks labs enters the story. The company, cofounded by designer Joshua English and green building expert Chris Magwood (also manager of RMI's Carbon-Free Buildings program), has developed zero-frm: a patented structural mycelium biocomposite made from mycelium, hemp hurd, and organic cotton. The company holds US Patent 11,866,691 for its structural mycelium-based composite and has been selected for Third Derivative's climate tech accelerator and a research collaboration with Argonne National Laboratory.

Independent endorsements support parts of the structural claim. Wil V. Srubar III, PhD, associate professor at the University of Colorado Boulder, noted that zero-frm "has very different material properties than other mycelium based biocomposites," with surface hardness, rigidity, and durability that "open up brand new opportunities for mycelium-based materials to serve in actual load-bearing applications." Dr. Andrew Dent, EVP of Research at Material ConneXion, called it unlike anything else in the landscape of mycelium composites.

The measured data tells a grounded story. okom wrks has demonstrated compressive strength of approximately 1 MPa, which the company describes as sufficient for framing lumber substitution when spaced 12 to 16 inches on center. Their target is 3 MPa. For context, standard framing lumber in compression runs at 30 to 40 MPa; structural concrete at 20 to 40 MPa. Magwood himself was candid: "The very nature of mycelium is lightweight, and its best strength is tensile, not compressive." What zero-frm appears to represent is a viable bio-based framing substitute, a carbon-storing material that could replace dimensional lumber in walls, with hempcrete cast around it as infill.

That combination, a bio-framed and hempcrete-infilled wall assembly using entirely carbon-negative materials, is the forward-looking design question commercial architects are beginning to ask. If zero-frm's compressive performance improves and structural testing completes, the wall system it enables would sequester carbon at every layer: from framing to insulation to finish plaster, with no petrochemical content anywhere in the assembly.

What Real Estate Has Not Priced In

The global hempcrete market stood at roughly $570 million in 2024. It is forecast to reach $2.24 billion by 2034. North America alone is projected to grow from $9.5 billion to $14.7 billion over the same period, driven by regulatory adoption and the growing cost of carbon in building specifications. LEED and PHIUS certifications now factor embodied carbon into scoring, which gives hempcrete a structural advantage that no petrochemical insulation product can match: carbon stored in the wall is carbon removed from the atmosphere, countable in lifecycle assessments.

The code event most comparable to what happened with hempcrete in 2024 is what happened with straw bale construction in 2018, when it received its own IRC appendix. In the years following that approval, straw bale moved from permit-by-exception to permit-by-standard in jurisdictions across the country. Hempcrete has better fire ratings, better thermal performance data, a larger European precedent base, and more active institutional investment. The conditions for a faster adoption curve are present.

What is missing is the real estate community's recognition that this has already happened. The 2024 IRC is not a proposal. It is published code. Austin is already enforcing Appendix BL. Minnesota has adopted it. The DOE has committed capital. Hempitecture is scaling. Hillside is occupied. The market formation story is underway.

The walls are being poured. The carbon is being stored. The code exists. The builders who understood what happened in France in the 1980s and watched it not translate to the US for two decades now have the same opportunity, but this time with a regulatory foundation under them.