Hempcrete

Hempcrete, or hemp-lime, is a bio-composite material used primarily as insulation and infill in walls. It is made from hemp hurds (also called shives) mixed with a lime-based binder. Hempcrete is typically employed in non-load-bearing walls within timber or steel-frame construction, where its low weight, breathability, and thermal performance are advantageous.

Hemp shives are the core by-product of hemp fiber processing and provide internal porosity. Binders include lime putty, hydraulic lime (NHL), or cement-lime blends. The mixture is usually dominated by hemp shives by volume, with a smaller proportion of binder. Curing occurs mainly through carbonation of lime; hemp contributes to insulation and moisture handling but does not carry structural load.

Thermally, hempcrete has a low thermal conductivity, typically around 0.08 to 0.12 W/m·K depending on density and mix. It is moisture- and vapor-permeable, enabling walls to buffer humidity and manage capillary moisture. The material is lightweight, provides some sound insulation, and is generally non-toxic and fire resistant due to the lime binder.

Construction typically involves forming a frame and filling with hempcrete, then applying lime plaster on both faces. The material dries and cures slowly; it requires proper detailing to prevent weather exposure during curing. Hempcrete walls are not load-bearing and rely on the frame for structural support; careful detailing is needed for airtightness and moisture control.

Historically used in parts of Europe since the Middle Ages, hemp-lime construction saw renewed interest in the late 20th century as a sustainable alternative to conventional materials. Environmental claims include low embodied energy and carbon sequestration during hemp growth, though lime production and curing influence totals. Regulatory acceptance varies by country, with different standards and building-code treatments for hemp-based systems.