Hempcrete — also called hemp-lime — is a lightweight bio-composite made by mixing hemp hurd (the woody core of the stalk) with a lime-based binder and water. Despite the name it is not a structural concrete: it is a non-load-bearing infill packed or cast around a timber or other frame, valued mainly as insulation.
Its appeal is a rare combination of properties — good thermal performance, breathability that buffers indoor humidity, fire resistance, and notably low embodied carbon. Because the hemp locks up CO2 absorbed during growth and the lime slowly reabsorbs more as it cures, a hempcrete wall can act as a modest carbon store over its service life.
Hempcrete crossed an important threshold in the United States when the 2024 International Residential Code added Appendix BL, 'Hemp-Lime (Hempcrete) Construction' — the first time the material appeared in a model building code, allowing its prescriptive use in low-rise dwellings wherever a jurisdiction adopts the appendix. That move is widely seen as a step toward mainstream hemp construction. See hurd and construction.
