Hempcrete is Carbon Negative - so more carbon is taken out of the atmosphere by the growth of the hemp plant than is emitted as a result of hempcrete’s production and its application on site.
What does this mean?
Buildings are the largest energy consumers and greenhouse gases emitters, both in the developed and developing countries. Urgent changes are therefore required relating to energy saving, emissions control, production and awareness of materials used in the construction process.
The construction industry is responsible for more than 60% of the UK’s total carbon emissions, both through energy used in the construction process and the energy used by the occupant once the building is in use. Ambitious targets have been set by governments to meet global deadlines for lowering carbon emissions (Carbon Budgets). The Climate Change Act also calls for a significant reduction in carbon emissions by 2050. As a result the construction industry has seen a rise in the standard and amount of insulation used to meet regulation, as well as schemes for a number of lofts and walls being insulated and boilers upgraded, including moves to low-carbon heat such as ultra-efficient heat pumps on exiting homes.
Unfortunately little focus if any has been put upon the “embodied energy” or the amount of carbon used to create these materials. This accounts for its extraction from raw materials, manufacturing process, transport, application, and the energy used in recycling or replacement of the material at end of life.
At present the materials used in upgrading the efficiency of buildings and homes in the UK are high in embodied carbon. However effectively we insulate our buildings, and whatever low carbon systems we install, we are still failing to offset the huge amount of embodied carbon associated with constructing the building in the first place, and eventually disposing of non-recyclable materials at the end of its life.
Because the hemp plant absorbs a very high level of atmospheric CO2 as it grows, and because the production and application of hempcrete is quite a low-tech process, what is more the hemp can be sourced relatively locally, the end result is a material that is carbon negative, in other words better than carbon neutral!
In addition the hemp plant is naturally pest-resistant and weed-suppressant, and it eliminates the need for chemical fertilizers and insecticides. It requires very little fertilizer, and is deep rooting; returning key nutrients to the soil and improving the condition of farmland by breaking up the soil to a significant depth. These qualities make it an ideal “break crop” and farmers in the UK often grow it between plantings of other crops such as winter wheat. The reduction in pesticide use brought about by growing hemp also helps to support biodiversity in our fragile eco-system, and promotes the survival of beneficial pollinating insect species.
Hemp: A truly sustainable material
The reason the hemp plant absorbs so much carbon dioxide is because it is a tall, fast-growing plant. In the UK climate it grows up to 4.5 metres in 4-5 months. Industrial hemp has long been grown for the production of its fibre into textiles, rope, sails or even car body panels. Hemp has also been grown for its seed, which has been shown to contain beneficial oils and omegas for humans to consume. The strong woody cellulose core of the stem is the part that is chopped up, to become Hemp Shiv and used for building. The shiv is a waste product of these other industries, meaning the whole plant gets used. Although hemp's cousin plant is Marijuana, hemp contains none of the potency of the drug and all of the products related to industrial hemp are safe.
Compared to timber, the fast growing hemp plant, which replenishes itself every year in just a few months, is very quickly renewable, making it a truly sustainable material. The extra strength and protection which the lime binder in hempcrete gives to the timber structural frame in a hempcrete wall means that faster-growing softwoods can usually be used for the frame, further increasing the sustainability of hempcrete buildings.
The Hemp shiv we use in the UK is grown in Yorkshire and processed on the farm before being delivered directly to site, cutting down on the energy used to transport hemp shiv for building. France also has thriving hemp industries and shiv can be imported, which can still be considered a locally sourced material, especially when compared with many other modern insulation materials.
Hemp can be grown and processed all over the world, in a range of soil types, as long as the climate is not too arid so can be considered a globally local crop. The processing of hemp is also relatively simple when compared to synthetic insulation materials which take high energy chemical processes to produce. In the production for example of Rock wool, the raw materials have to be extracted, then transported (often shipped) to chemical factories abroad where it is cheaper to produce the finished insulation, before being shipped back to the countries where it is needed. In addition synthetic insulations are often made from petrochemicals derived from oil and commonly treated with toxic chemicals. Potential chemical leaks and pollution from factories such as these pose their own risk to the surrounding environment. Such materials are rarely recyclable and you can easily see the huge environmental impact they have. Due to the large amount of embodied carbon these materials carry, it will take many decades to cancel out any carbon savings that increased insulation would create.