A soft dust of lime hung in the morning light as carpenters packed a pale, fibrous mix between timber studs. It smelled faintly of earth after rain. In that moment, the room felt different—quieter, drier, somehow calmer—as if the walls themselves were learning to breathe.
For decades, builders who loved this hemp-and-lime material—hempcrete—worked on the edges, persuading local inspectors one project at a time.
Now, at last, the center of gravity is shifting: hemp-lime construction has made its way into the United States’ model residential building code, a step that could change how American homes are built.
A Quiet Rule Change With Big Consequences
In the 2024 International Residential Code (IRC), hemp-lime appears as Appendix BL, a set of clear rules that treat it as a non-structural wall infill system for one- and two-family dwellings and townhouses.
It outlines what hemp-lime can and cannot do, and how to design with it, so plan reviewers have something concrete to go by rather than improvising exemptions. In plain terms: it moves hempcrete from “special request” to “recognized method.”
The path is practical, not ideological. Appendix BL allows prescriptive use—without extra engineering—in regions of low seismic risk for buildings up to two stories; elsewhere, engineers can still design with hemp-lime, but they’ll need to stamp the drawings.
As with all IRC appendices, jurisdictions must explicitly adopt it, yet because the IRC underpins codes in nearly all U.S. states, the on-ramp is finally visible nationwide.
What Hempcrete Brings Indoors
Hemp-lime is not a drop-in replacement for concrete; it is a biobased infill that pairs with a structural frame. Its virtues are quietly domestic. The material regulates moisture, helping keep interiors dry and comfortable. It resists pests and rot, and—thanks to the mineral binder—performs well in fire.
Perhaps most compelling for a warming planet: hemp captures carbon as it grows, and a portion of that carbon remains locked in the finished walls, pushing projects toward lower embodied-carbon footprints. Architects from Australia to Europe have embraced these qualities, citing pleasant acoustics, thermal stability, and the way a room “feels” when the walls can breathe.
Those performance claims are gaining formal backing. In 2024, a spray-applied hemp-lime wall assembly endured a 1,700°F exposure for one hour in an ASTM E119 fire test at Intertek—progress toward fire-resistance ratings recognized by U.S. code officials. Further testing is ongoing, but the early datapoints support what builders have observed for years.
From Policy To Work Sites
Momentum matters most when it moves beyond paperwork into practice. In Austin, Texas, city leaders voted to adopt Appendix BL for homes and small multi-unit buildings, with changes taking effect in 2025.
The rationale was straightforward: align building rules with climate goals, expand healthier options for residents, and open doors for local suppliers and farmers. “By embracing hempcrete, we can support local farmers and businesses,” said a city policy strategist when the measure advanced.
On tribal land in Minnesota, the Lower Sioux Indian Community has gone further—growing hemp, processing it locally, and building houses with the material as a pathway to healthier homes, jobs, and greater sovereignty.
In public remarks, community leaders have framed the effort simply: “a roof over our people’s heads,” with walls that better resist mold and fire, in a place long underserved by conventional housing supply. Their hemp campus—roughly 20,000 square feet—anchors a vertically integrated program that trains workers and keeps value in the community.
A Wider Lens On Carbon And Craft
Globally, cement accounts for a large share of industrial emissions. That’s why alternative envelope systems that lower operational energy and store biogenic carbon are drawing attention.
Even in mainstream coverage, hemp-based housing is being explored as one of several practical ways to cut construction’s footprint—alongside better design, material efficiency, and factory-built methods. The appeal is not that hempcrete can do everything, but that it does a few essential things very well.
Crucially, the new code status shortens the distance between curiosity and construction. Before Appendix BL, a builder often had to convince a local official under “alternative materials” provisions, a process that added uncertainty and cost.
Now, plan reviewers have prescriptive language; designers have a shared vocabulary; and homeowners can evaluate hemp-lime alongside familiar options like cavity insulation or exterior mineral wool, with fewer bureaucratic unknowns.
Not Hype—Homework
None of this is a magic wand. Scaling hempcrete requires real-world work: more decortication and milling capacity to produce consistent hurd (the woody hemp core), training for installers, and product supply chains that can keep pace with interest.
Yet these are practical problems, not existential ones, and communities are already tackling them. Trade groups and nonprofits have published guidance, architects are compiling details, and early adopters are sharing test data and field lessons so the next project gets simpler.
People First, Then Policy
What stays with you after visiting a hemp-lime site isn’t a statistic—it’s a feeling. The ambient quiet. The absence of that synthetic “new house” smell. The way temperature drifts less from noon to night. Home is a deeply human technology, and the codes that govern it are, at their best, instruments of care.
The addition of hemp-lime to the model code does not mandate a trend; it dignifies a choice. It lets a family in Arizona or Vermont—or on tribal land in Minnesota—ask a different set of questions about health, carbon, and craft, and get a fair hearing from the permitting desk.
Looking Ahead
If adoption spreads, expect a modest but meaningful recalibration: more timber-framed shells filled with gentle, mineral-bound plant fiber; more local growers with a market beyond CBD; more homes designed for the steady comfort of vapor-open walls. It won’t replace concrete foundations or steel beams where they’re needed.
It will, however, help America build more like a living system—sequestering a little carbon, storing a little heat, and giving the people inside a better day-to-day experience. That is a hopeful trajectory worth building on.
Sources:
Ganjapreneur
Hemp and Block
