Hempcrete as Construction Material

Hempcrete (hemp-lime composite) mixes hemp hurds (particle size 5–30 mm, 160–200 kg/m³ bulk density) with hydraulic lime binder (Natural Hydraulic Lime NHL3.5 or NHL5, lime:hemp ratio 1:1.5–2.5 by volume) and water (water:binder ratio 0.5–0.8) to produce a carbon-sequestering insulating infill wall material. Cast density of 250–400 kg/m³ is 3–5× lower than concrete (2,400 kg/m³). Thermal conductivity of 0.07–0.12 W/m·K (dry, ISO 10456) provides thermal resistance equivalent to 300 mm hempcrete wall achieving U-value of 0.20–0.35 W/m²·K. Hygroscopic buffering capacity of 150–250 g/m² at 50–75% RH transition regulates indoor humidity passively — reducing HVAC energy load by 15–25% in moderate climates. Carbon balance: sequestration during hemp growth (1.63 kg CO₂/kg hurd) minus lime calcination emission (0.44 kg CO₂/kg lime) produces net carbon-negative wall material of −0.5 to −1.0 kg CO₂e/kg hempcrete. Compressive strength 0.2–1.0 MPa (non-structural, EN 772-1) requires structural frame; tensile strength is negligible.