Cannabis is a remarkable plant that has been used throughout history for a wide variety of different purposes. It is believed to have first been cultivated in Eurasia and then spread by humans throughout the rest of the globe. The plant can provide food, fiber, shelter, clothing, medicine, nutritional fats and amino acids, spiritual aid, fuel, and even has beneficial essential oils! There are many unique variations of the cannabis plant throughout the world, the distinct cultivars specific to certain locations are known as landraces. These unique expressions of the same place arose and diversified as cultures throughout the world selectively bred the plant for their desired purpose. It was discovered in a bridge abutment built in the 6th century in France, that’s a long lifetime! Cannabis has been a very beneficial plant throughout history and it was only in the last century did its use drop. A decline in demand for fiber along with a rise in competition from other natural plant fiber sources reduced interest in hemp. This, coupled with the propaganda campaign against the cannabis plant, led to the crop being prohibited in most of the world during the late 20th century. The distinction between cannabis plants that can be used as a psychoactive drug (marijuana) and plants that can be used as a building material (hemp) generally lies in the amount of THC (tetrahydrocannabinol) present on the plant. THC is the main chemical compound that produces a high from cannabis and it is present in only tiny amounts in industrial hemp. Industrial hemp is generally very tall whereas marijuana plants are bushy and heavily laden with dense flower buds.
Renewed interest in the cannabis plant has sent people searching the world to find undiscovered landrace cultivars that could provide a key sustainable source for many of humanity’s needs and desires. Hemp may help the construction industry to transition away from highly polluting, carbon intensives solutions, to more sustainable ones.
One of the most common ways that hemp is used in construction is as hempcrete bricks that infill between a load bearing frame. The inner, woody core of the hemp plant is combined with a lime-based binder to form an insulating block that weighs only 1/7th the amount of concrete. Fully cured bricks even float in water. Hempcrete has good thermal and acoustic insulating properties, and it can passively regulate humidity in a built environment, this helps to decrease the risk of vapor condensation and increase thermal comfort. The interaction between the silica in hemp and lime causes hempcrete to mineralize over time which makes it rot, mold and fire resistant. Different formations, in terms of density and composition, of hemp mixtures can be used for different purposes, from block walls to filling materials, to roof and floor materials, to indoor and outdoor plasters. Hemp captures CO2 as it grows and the carbonation process, where the silica in hemp bind with lime and cement, also absorbs more CO2 and stores it for the lifetime of the building. This means that hempcrete blocks have a negative carbon footprint and if they were used widely, they could help reduce the massive environmental impact of the construction industry. Exact estimates of hemp’s carbon storage ability and environmental sustainability very depending on site climate and soil conditions.
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LimeTechnology, A. (2017, 06 07). What is Hempcrete? Retrieved from american limetechnology: http://www.americanlimetechnology.com/what-is-hempcrete/
Zampori, L., Dotelli, G., & Vernelli, V. (2013). Life Cycle Assessment of Hemp Cultivation and Use of Hemp-Based Thermal Insulator Materials in Buildings. Environmental Science & Technology.