Hempcrete

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Hempcrete: (A) brick, (B) brick with text "Made from hemp hurds, lime and water. As it cures it draws carbon dioxide from the atmosphere, and petrifies the cellulose into stone. Within 50 years it is solid as a rock. This building technique is at least 2000 years old." (C) Construction blocks made from hempcrete (in France). (D) Hemp interior thermal insulation blocks. (E) Hemp lime building under construction in Northern Ireland. External wall after removing the temporary shuttering.
Close-up of hempcrete wall. "The one-storey building uses a prefabricated modular system and a biomaterial called Hempcrete made up of hemp core, lime binders and water. Both features are new to Singapore. Hempcrete is ideal for humid climates as it produces good indoor air quality. It is also very durable, and resistant to pests, mould, mildew and fire."

Hempcrete is a mixture of hemp hurds (shives) and lime used as a material for construction and insulation. It is marketed under names like Hempcrete, Canobiote, Canosmose, and Isochanvre. Hempcrete is easier to work with than traditional lime mixes and acts as an insulator and moisture regulator. It lacks the brittleness of concrete and consequently does not need expansion joints. The typical compressive strength is around 1 MPa (around 1/20 that of residential grade concrete). Hempcrete's density is only 15% that of traditional concrete.

Eco-credentials: The hemp plant used as the aggregate in hempcrete absorbs so much carbon during its rapid growth that, even after the energy used in production of the lime binder, transportation and on site construction, more CO2 is locked up in a hempcrete wall than is used to build it.

Pros and Cons

Pros

  • made entirely from natural materials and is naturally fire- and pest-resistant
  • Hempcrete is a sustainable/renewable material
  • carbon-negative
  • vapor-permeable
  • In historic buildings hempcrete works in harmony with the original materials

Cons

  • relatively new material, quite different from most conventional building materials; it may take time until some key concepts and techniques are understood.
  • Architects who are not used to working with hempcrete and other natural materials may not find it easy to detail buildings correctly when using these materials.

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