When you think of hemp you may picture the hemp plant itself- or, you might imagine it’s sister plant, marijuana. You may have even used a variety of hemp products like hemp milk, paper, linen, rope, and even hemp beauty products. But did you know that this versatile plant can also be used to make construction materials? Hempcrete (or hem-line in the UK), is mostly used as a sustainable alternative to insulation products like fiberglass, rockwool, and foam. Recently, with the legalization of hemp products in the United States, hempcrete has become a more viable insulation solution. Read on to learn more about the uses and benefits of hempcrete in the construction industry.


What is Hempcrete?

Hempcrete is a biocomposite material made from a mixture of hemp hurd, limewater, and sand. To make hempcrete you combine hemp hurd- the inner woody core of the hemp plant- and a lime-based binder- like limestone- and water to form a paste. You can then pack or spray this paste into the frame of a structure to act as insulation. Alternatively, you can form hempcrete into blocks which you can install into the frame. Builders typically use plaster to coat the hempcrete and create a smooth-walled finish. 


*Despite its name, hempcrete lacks the compressive strength to replace materials like concrete. Because of this, it cannot be used structurally in building projects. 


How Common is Hempcrete?

Currently, the use of hempcrete is still very rare. According to the U.S Hemp Building Association and yaleclimateconnections.com, less than 100 homes have been made using hemp. This is likely because up until a few years ago, hemp was illegal in the United States. 


Hemp Was Illegal in the USA until Recently

Believe it or not, cultivating hemp plants was illegal in the United States until 2018. This is because- technically- hemp and marijuana are the same plant- cannabis. Both plants do contain tetrahydrocannabinol (THC)- which is the psychoactive substance that can make a user intoxicated. However, while marijuana plants contain up to 30% THC, hemp plants only contain up to .3% THC. 


Marijuana and hemp look slightly different too. Hemp plants are typically a hybrid of male and female plants and have thick hearty stocks. Hemp plants are also tall, quick growing, and can thrive in many climates. They have no psychoactive effects and are used to make hemp oil, CBD oil, and many different materials- like hempcrete.


Marijuana plants are female plants and have distinctive flowering buds. These buds contain the most THC and are used for medicinal and recreational purposes because of their strong psychoactive effects. Unlike hemp plants, they must be grown under carefully controlled conditions that keep humidity, temperature and moisture at ideal levels. 



If Hemp is not Psychoactive, then why was it Illegal?

Humans have been using and cultivating hemp for thousands of years. Ancient civilizations used hemp for all kinds of purposes- medicinal and practical. The plant is likely a native of Central and Southwest Asia and made it to the United States in around 1545. Hemp then became an important crop in the U.S.- including during both world wars- until the mid 19th century. 


However, attitudes towards drugs began to shift and in 1937 the Marihuana Tax act was introduced to control the growth, possession, and distribution of marijuana. Unfortunately, because hemp is technically the same plant as marijuana, it got caught up in the bill. Hemp became difficult and expensive to cultivate. 


The real nail in the coffin for hemp growth came in the 1970’s with Nixon’s Controlled Substances Act. Marijuana was effectively prohibited and its growth and possession was criminalized. And, just as it had in 1937, hemp was given the same status as marijuana and was completely outlawed.



2018 Farm Bill Legalized Hemp 

Hemp finally became legal again in 2018 with the much anticipated Farm Bill. The bill allows people to possess, cultivate, and distribute hemp and hemp products. Now, with regulations, farmers will be able to grow hemp and create hemp products- which will likely allow for more products like hempcrete to be made in the USA.



Benefits of Hempcrete


  • Nontoxic:

    Hempcrete is nontoxic to produce and will not give off any toxic fumes during its lifetime. Hemp generally uses less pesticides than other plants during the growing process and hempcrete does not require any heat to be produced. 


*It should be noted however, that growing hemp requires a lot of fertilizer which can be damaging to the environment. Additionally, the production of hempcrete creates a lot of caustic dust. Therefore, proper PPE breathing protection is essential for builders during the hempcrete mixing process. 


  • Sustainable:

    Hemprcrete is more sustainable than its petroleum-based counterparts. Many other types of insulation require petrochemicals in their production. This includes standard insulation materials like fiberglass and wool-based insulation. Luckily, hempcrete does not require any petrochemicals or synthetic materials. Additionally, hemcrete is a carbon-sequestering material. This means that it literally sucks CO2 out of the atmosphere. In fact, in one study, hempcrete was found to be able to sequester 19 pounds of CO2 per cubic foot–  which is the equivalent of the yearly carbon emissions of three refrigerators!


* Petrochemicals are both toxic to people and animals and bad for the environment: Petrochemicals, made from fossil fuels, release a lot of methane and carbon dioxide into the environment and are responsible for 18% of CO2 emissions. And it doesn’t end there- petrochemical-based products release toxic fumes- even after production- which can be harmful to animal, human, and marine life. Additionally, unlike hemp which is a renewable resource, petroleum is a finite resource which will eventually run out- making the development of renewable energy and materials- like hempcrete- incredibly important.  


  • Fire Resistant:

    Hempcrete is a non-flammable material that may be fire resistant. Although the studies of hempcrete fire resistance are minimal, a US study found that hempcrete was impressively fire and heat resistant during a standard surface burn test of the material. Another Australian study found that flames were unable to penetrate a 200 mm thick hemp concrete wall. The wall was exposed to a 600 mm high flame that  burned directly against the wall for 60 minutes. This means that hemprete could potentially prevent fire from penetrating a building for around an hour (although more studies are needed). A crucial amount of time that would allow for evacuation or even give officials time to put out the blaze. 


* Another great thing about hempcrete is that it is not made with petrol or other dangerous chemicals. This means that when burned it does not release toxic or environmentally damaging fumes. And -just in case you’re wondering- no, burning hempcrete will not get you high the way marijuana plants do. Hemp is naturally very low in THC and does not give off any psychoactive effects.


  • Mold Resistant:

    Hempcrete is antimicrobial and antifungal and is generally resistant to mold and mildew. This can be ideal for people who live in wetter and warmer climates who struggle with mold growth. 

  • Good Thermal Resistance:

    Because hempcrete is most often used as an insulating material, it is very important that it has good thermal resistance. Hemcrete has an R-value-  of 2.4 to 4.8 per inch, which isn’t the highest or lowest rating. However, other factors like the binder used, moisture content, and density of the hempcrete can impact these numbers. 


*In insulation, an R-Value “tells you how well a type of insulation can keep heat from leaving or entering your home. Insulation R-values vary based on the type, thickness and density of the insulation material. Typically, a higher insulation R rating means better climate control and better energy efficiency for your home.” 


  • Potentially Affordable:

    Because hempcrete is not a typical insulation material, it used to be considerably more expensive- up to 30% more in fact. However, with hemp’s legalization, more and more hemp growers and distributors have been popping up in the United States. This has cut down import costs and made the material much cheaper in some cases. The average hemcrete is still a little more expensive than regular insulation, but is becoming increasingly comparable to standard insulation and thus moving toward an affordable price.


The Future of Hempcrete

With the relatively new legalization of hemp, the future of hemcrete looks bright. The benefits of hempcrete- sustainable, non-toxic, mold- resistant, fire-resistant and more- make it an ideal material for future eco-friendly building projects. Hempcrete is still uncommon and expensive in the United States. But, with more and more farmers able to grow hemp in the US, hempcrete could become an option that is both more sustainable and comparable in price to traditional insulation. 


Will your next home be insulated with hemp?



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