Material · Composite · Assembly
Hempcrete
Hemp-lime · hemp hurd + lime binder
A bio-composite of hemp hurd (the woody stalk core) bound with lime, cast or sprayed around a structural frame. It is insulation, thermal mass, and humidity regulation in one monolithic wall — and it is not structural.
Why it matters
Hempcrete is the most talked-about natural wall system in North America since its 2024 adoption into the residential code (IRC Appendix BL), and the claims around it need sorting: yes, it stores carbon, buffers humidity, and resists mold through lime's pH; no, it does not hold up the roof, insulate as highly per inch as foam, or dry overnight.
Benefits
- Walls that insulate, buffer humidity, and add thermal mass in one material
- Lime's high pH resists mold and pests without treatment
- Genuinely carbon-storing: the hemp sequesters more CO₂ than the lime releases
- Vapor-open assembly — no condensation traps, no sheet plastics
- Excellent acoustic damping and fire performance in tested assemblies
Best applications
Rooms: Whole home
Performance
Watch-outs
- Non-structural — it wraps a frame; budgets must carry both
- Cast walls need weeks of drying before finishes; schedule accordingly
- R-value per inch is modest (~R-2.1); walls are thick by design
- Experienced installers are scarce; workshops and specialty contractors dominate
- Must be finished vapor-open (lime plaster) — cement stucco or acrylic paint suffocates it
What to verify
Finish, binder, sourcing, and installation conditions to confirm before specifying.
- Code path: IRC 2024 Appendix BL adoption status in your jurisdiction
- Installer experience with cast vs spray-applied hemp-lime
- Drying schedule before finish application
- Vapor-open finish spec inside and out
Certifications to look for
The labels that separate the real material from the marketing version.
IRC 2024 Appendix BL
US residential code appendix covering hemp-lime construction
Sources
Information verified July 2026.