Hemp, the Material
Hempcrete is the woody core of the hemp stalk — the hurd — bound with lime and water. Eight numbers explain why architects are paying attention.
Density
Cured hempcrete weighs 275–500 kg per cubic metre, a fraction of concrete's roughly 2,400. Lighter walls mean lighter foundations, less transport and easier handling on site.
275–500 kg/m³ · seven times lighter than concrete
Thermal
With a thermal conductivity of 0.06–0.09 W/m·K, a thick hempcrete wall insulates on its own — no separate insulation layer. Its mass also slows heat through the wall, evening out day-to-night swings.
λ 0.06–0.09 W/m·K · breathes at thickness
Compressive
Hempcrete is not load-bearing. It is cast around a timber frame that carries the loads, while the hemp-lime wall insulates, stiffens the frame and becomes the finished surface.
0.4–1.0 MPa · non-structural, frame it
Bast tensile
The long bast fibres on the outside of the stalk are among the strongest plant fibres. They go into textiles, rope and composites — one crop gives both hurd for building and fibre for industry.
300–800 MPa · single fibres reach 1,500
Vapor permeable
Hempcrete lets water vapour pass and buffers humidity: it takes moisture in when the air is damp and releases it when it dries. Rooms stay comfortable without mechanical help, and walls don't trap condensation.
μ 4–6 · regulates indoor humidity passively
Fire class
Lime-coated hurd chars rather than burns. With a suitable binder, hempcrete can reach Euroclass B-s1, d0 — limited contribution to fire, little smoke, no burning droplets. The class always depends on the tested product.
B-s1, d0 · achievable with the right binder
Carbon
Hemp draws CO₂ from the air as it grows, and the lime binder reabsorbs some CO₂ as it cures. The result is roughly 110 kg of CO₂ held in every cubic metre of wall — for as long as the building stands.
≈ 110 kg CO₂ stored per cubic metre
Lifespan
The Maison de la Turque in France was restored with hempcrete in 1986 and still stands. Kept dry and able to breathe, a hempcrete wall is expected to last as long as the frame around it.
40+ years · Maison de la Turque, 1986
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