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Benefits and constraints


Hempcrete provides high vapor permeability because of the mixture's ability to easily absorb or release water vapor from the air. In frame structures, hempcrete mixtures can be used as filling materials in infill walls. Increasing the density of the mixture allows the production of roof or floor insulation hempcrete materials. Decreasing the density allows the production of indoor and outdoor plasters. Hempcrete blockwalls can be laid without any covering or can be covered with finishing plasters. This latter uses the same hempcrete mixture but in different proportions.


The fact that the mixture contains a plant-based compound introduces the caution against water and rising damp levels. Hempcrete walls need to be built with a joint between the wall and the ground in order to avoid capillary rising as well as water runoff at the wall base. Moreover, hempcrete block can only be installed above the ground level. External walls need to avoid rotting of shives by implementing protection by the rain gale with sand and lime plaster. The exterior of a hempcrete based assembly needs these protections, but the interior side of an assembly can stay exposed.


Life cycle impacts


Just like any crop, hemp absorbs CO2 from the atmosphere while growing, so hempcrete is considered a carbon-storing material. Accordingly, this CO2 will be stored in the hempcrete after fabrication and for the duration of hempcrete life allowing positive environmental benefits. The specific amount of carbonates in hempcrete actually increases with the age of the block. The amount of CO2 capture within the net life cycle CO2 emissions of hempcrete is estimated to be between -1.6 to -79 kg CO2e/m2. There is a correlation that increasing the mass of the binder which increases the mixture density will increase the total estimated carbon uptake via carbonation.


The main cause of environmental impacts for hempcrete comes from the production of the binder. Reports have estimated that 18.5% - 38.4% of initial emissions from binder production can be recovered through the carbonation process. The binder is produced by the calcination of lime which takes place in kilns at very high temperatures. The transport phase poses embodied energy impacts since it involves the consumption of diesel. The diesel consumption also occurs due to the functioning of machineries used for hemp shives production.


Advantages of Hempcrete


Hempcrete breathes, allowing moisture to evaporate (no mold), does not off-gas, and is avoided by termites. The non-toxic and lightweight properties of hempcrete also ensure it is easy to move around a job site. Hempcrete does not shrink, maintains a steady temperature, and can also increase in strength over time.


Disadvantages of Hempcrete


While this may not qualify as a real disadvantage, hempcrete cannot be used as a foundation structure due to its low compressive strength. In most cases, it is not a load-bearing material. A project that could utilize a lightweight foundation could take advantage of hempcrete instead of concrete, providing it adheres to local building codes and is approved by an engineer. While research and development around the use of hempcrete are still in infancy, preliminary findings are incredibly positive.


What is the R-value of Hempcrete?

Hempcrete has an R-value of 2.08 to 2.4 per inch, compared to 0.1 to 0.2 per inch of concrete. Hempcrete can also achieve a higher R-value than fiberglass batt and cotton batt, whose R-values are, at most, 3.8 and 3.7, respectively. The thermal performance of hempcrete can be impacted by several variables, including the type of binder used, moisture contents, and density.


How Strong is Hempcrete


The compressive strength of hempcrete is 1/20 that of concrete, coming in at 1 MPa, meaning it can't be used as a foundation material or in situations where it may be load-bearing. It's resistant to cracking due to its low density making it an attractive alternative to areas prone to earthquakes.


Hempcrete also breathes, allowing moisture to evaporate (no mold), does not off-gas, and is avoided by termites. The non-toxic and lightweight properties of hempcrete also ensure it is easy to move around a job site.


While hempcrete may be growing in popularity, it's still not widely available on the market. Nonetheless, hempcrete has a comparable cost to other insulation options and will become more affordable as production volumes increase.


How Long Does it Take to Grow Hemp


Hemp fiber and seeds are usually ready for harvest in two months. The rapid growth rate allows it to out compete other raw materials because it is rapidly renewable and can be used in a wide variety of diverse industries. For example, hemp can produce about four times as much paper as trees per acre. The difference, of course, is that trees take years to reach maturity.


Bottom Line


As a society, we are becoming more aware and conscious of the world in which we live and the impact we can make (both negatively and positively) on our environment. The adoption of green construction is growing in popularity to help reduce carbon emissions.


One such method involves building with hemp plants, which has become known as hempcrete. The resurgence of the hemp industry has opened doors to create innovative ways of building environmentally friendly homes. Additionally, it is extremely cost-effective and one of the best ways to insulate houses and buildings throughout the year.


Hempcrete is a mixture of hemp hurds, lime binder and water. Hemp holds a high silica content that helps it to bind well with lime. The end result is a lightweight, cementitious and insulating material which weighs only one-eighth to that of concrete. Most importantly, it is able to absorb and store large amounts of carbon dioxide gas, making it a carbon-reducing option.


The benefits and potential uses of hemp in the building industry make it worth checking out as the trend continues to grow and becomes widely available. At LONE STAR HEMPCRETE™, we like hemp because it represents just one of many innovative, more sustainable products in the building industry and a bright spot for our future!