Hemp lime construction and ecological sustainability
A construction material which has as its major ingredient a fast growing renewable resource is hard to beat when you are looking for a sustainable building material. Expanding farming of this high biomass fibre crop for housing also has the potential to make a significant contribution to Australia’s emissions reduction strategy. Contingent on the number of internal walls, an average 135 sq m home at a minimum contains between 2 – 3 tonnes of Hemp.
AHMC’s Binder materials were designed to minimise the carbon footprint of hemp construction and to maximise affordability. Our R & D was focussed on life cycle analysis and we investigated ways in which to minimise the minerals intensity of the materials by replacing some of the mined, heated materials in the Binder with locally sourced sand. This gives our material the strength to be used for external walls at a thickness of 200mm. Locally sourcing sand avoids a drying process and minimises packaging and freight. Compared to some of the more commonly available European Binders for hemp construction we use 56 kgs per cub m less mined heated materials.
Australia has abundant lime resources. While lime production does have a significant energy footprint (hydrated lime is heated to 900º C), in Hemp lime construction, the energy or carbon released in the lime production process is reversed as the building material draws in carbon dioxide to cure.
All hemp lime construction materials contain small amounts of cementitious or pozzolanic materials which are heated to greater temperatures than hydrated lime. These materials may be naturally occurring as in hydraulic lime, magnesium oxide or volcanic ash and other pozzolanic materials or they may be bi-products of other processes.
The amount of these materials used vary with the application for the material e.g. sprayed walls, blocks, panels all generally include slightly higher levels of these substances. However despite this, Hemp Lime construction because of its renewable biomass content is still far ahead of conventionally used building materials.
The masonry material differs from conventional masonry, in that there is no kiln baking in the production of the final product adding to it’s profile as a low embodied energy building material. The curing process is carbonation, a process in which the material draws in carbon dioxide from the atmosphere to harden and cure.