Hemp
1-15 usd/kgHemp (Cannabis sativa) is cultivated for its fibres, seed oil and woody stem. While the seeds are a source of food, the core of the stem leftover from fibre production is converted into shives that are used for particle board and building materials, for example. In the past, the core has not been used intensively, but this is rapidly changing with the development of hempcrete, a biocomposite made up of hemp shives and lime-based binder.
The plants grow fast and tall, up to 4 m, helping to suppress weeds. And there are very few pests and diseases that affect these hardy plants – its very low protein content means it is not consumed by insects. This means pesticides are not needed. Even though restricted in some areas due to its association with marijuana, it is cultivated across Europe and Asia, and parts of Canada and United States.
The bast fibres are similar to those derived from flax, jute and ramie, and made up of 50-70% cellulose, 10-15% hemicellulose, 5-15% lignin and 5-10% pectin. Hemp contains more lignin than flax (linen), and the fibres tend to be less strong and stiff.
The majority of hemp fibre contains a mix of short and long fibres. The majority of it goes into nonwovens, such as for insulation, as opposed to fine textiles. It also goes into paper production. It is pricier than wood, but offers superior mechanical properties, and so tends to be reserved for speciality papers that require the extra strength it offers.
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Sustainability concerns


A bio-based composite of hemp shives and lime-based binder, hemplime materials such as hempcrete offer high thermal insulation as a result of the high proportion of air trapped within. The woody core has been an underutilised by-product of fibre production. Around 40-60% of the plant, it is typically added to particleboard, or used as animal bedding.
Hempcrete comes in many formats and formulations, such as prefabricated block, or loose mix, and can be used to build walls, floors and roofs. As with most other insulating materials, a framework is required, due to its low compressive strength. The major advantage of hempcrete – other than its very low environmental impact and safe ingredients without any toxic emissions – is that it allows a building to ‘breathe’. It is vapour permeable, and allowing moisture to pass through helps to maintain a healthy indoor environment for people and materials.
It is a material that can claim to be truly better than zero carbon, because not only does the hemp plant sequester CO2 that was absorbed during its lifetime (1.5-2.1 kg per kg of dry hemp), it can be composted and used as a soil additive at the end of its life. If the sequestered carbon is taken into account, then hempcrete has a positive environmental impact (as much as -1.6 kgCO2e/kg). Add to that the energy saved by using insulation, and it is clear why hempcrete is becoming a very valuable material in the circular economy.
It is very versatile and can be packed into cavities by hand, sprayed, or laid as pre-fabricated blocks. The main advantage of pre-cast units is that they arrive on-site already dry, so plastering can start immediately. In-situ hempcrete walls take several weeks to dry sufficiently for finishes to be applied. And in the winter, in situ hempcrete may be practically impossible, depending on the climate.