Hempcrete– a building material derived from the stem of the Cannabis plant– is now approved for use as a sustainable building insulation option, at a time when shortages plague the construction industry. According to the National Association of Home Builders (NAHB), the supply chain issues with building materials are at an all time high, with over 90% of builders having reported shortages in 2022. The delays in getting construction started have brought the average new-home build time from 4-6 months to over 8 months to be move-in ready, adding fuel to the fire in the ongoing housing crisis.
Hempcrete provides relief with density, thermal mass, and excellent acoustic performance. Hemp used in construction prevents mold growth, has a resistance to heat, and absorbs carbon while being a plant-based, non-toxic alternative to other monolithic materials used to build homes and businesses.
Hempcrete is a bio-composite made of the inner woody core of the hemp plant mixed with a lime binder. The hemp core has a high silica content which allows it to bind well when used together with lime. The result is a lightweight cement-like insulating material weighing about a seventh or an eighth of the weight of concrete according to American Lime Technology. Hempcrete buildings ten stories high have even been built in Europe.
To separate the hemp fiber from the woody core, the plant stalk is left to rot in a process called 'retting' for 4 to 6 weeks. Microbes begin to break down the pectin in the stalk and this facilitates separation. After retting, stalks are dried and then passed through toothed rollers, which then crush and break the woody core into smaller pieces. The end product is hemp hurd.
Placed in mixers for 1-2 minutes with a lime hempcrete binder and then stuffed by hand into the wall cavities, hemp blocks are sustainable building material often referred to as hemp concrete or "hempcrete". The material is lightweight and can be moved easily about the site in tubs and passed up bucket-brigade fashion to workers filling the cavities. Site clean-up is easy. Simply till it into the soil. Since its rediscovery by France in the 6th century, hempcrete has seen growing use in Europe. Industrial hemp is grown by certified commercial growers so the crop can be certified to be very low in THC and not psychoactive. Given it has survived 14 centuries, people expect hempcrete buildings will have a very long life.
Even if you aren’t up to designing your own hemp house, hempcrete can be useful for many smaller projects, and it’s incredibly easy to make if you know where to start. The only thing that you have to remember is that it’s similar to concrete in the way that it dries, so you do have to work relatively quick once you’ve mixed up a batch.
Farmers grow hemp in rotation with other crops such as barley or rye as a beneficial crop requiring no fertilizer, weed killer, pesticide or fungicide. It grows so thickly that weeds cannot grow, ironically. The crop following requires no weed killer because the hemp has driven weeds out.
Typically hemp mixed with a lime in walls must be used together to create a proper insulating infill. Four part hemp hurds, one part hydrated lime binder, and one part water is all you need to make hempcrete. Harvesting hemp shiv may be difficult but many general contractors have a processor with access, especially after the latest news - an increase in demand is to be expected. After acquisition, with lime spray applied, and used together with a frame - this sort of material can provide a permeability making it suitable for various projects and years of durability. Just fill up the form with hempcrete, compress it down, and once it's set, you're done. Remember to work quickly and avoid cold or wet environments, as these may change how your project dries. Make sure the binder used is appropriate.
While being highly insulative, regulating humidity to safeguard against asthma, being fire resistant, termite resistant, rodent-proof, and resists mold - hempcrete never rots. It preserves the timber house frame, generates zero landfill, sequesters carbon, while being nontoxic. The material that supports the vertical load is pressed while the timber frame and prefabricated blocks support the roof.
Concrete is a material used to create foundations and load-bearing structures. It’s heavy, cold to the touch, and has zero insulative qualities. Hempcrete, on the other hand, is super light. In fact, it is one-eighth the weight of concrete. It is non-load-bearing and best described as a masonry infill material with a porous, airy, fibrous composition. It is currently in the spotlight for several reasons: It’s a high-performance insulator, able to regulate the moisture content of the house (providing a sense of comfort and relief from allergies), and so eminently carbon-negative it can mitigate the carbon footprint of the entire house building process. For those who want to delve deeper into the building science behind the performance of hempcrete, you can learn more here.
In Australia, a fire test has been documented to simulate embers' attacks during wildfires, where there is a potential for fuel to accumulate at the base of the walls. This is a particularly worrying situation in Australia, where large forest fires routinely occur. No damage was observed on the 200 mm thick hemp concrete walls, which were exposed to a 600 mm high flame, burning directly against the wall for a period of 60 minutes.
In short, hemp-based materials provide adequate fire resistance so that residents can evacuate in time, reducing the spread of the fire and the risk of inhalation of smoke as it burns about locally. In other words, burning a wall of hempcrete will be very difficult and despite this fact, hemp is still an extremely stigmatized material in many countries.
This year the construction industry and lobbying groups like NAHB took to Congress to advocate for improvements like lower tariffs on lumber imports, but their recent win is a win for the cannabis industry as well: the approval of the use of ‘hempcrete’ in residential and commercial buildings. A sustainable and environmentally friendly product, Hempcrete is made from the Cannabis sativa plant and is a great alternative to traditional insulation materials like fiberglass. The lightweight, sustainable material is made from hemp fibers and lime that can be used as insulation, wallboard, and even flooring. With hemp being fully legalized federally, it's only a matter of time before this material becomes mainstream.
Made from the dried woody core of hemp stalks and a lime-based binder, hempcrete can be cast just like concrete. But unlike concrete and its binding cement, which accounts for about 8 percent of human-generated carbon dioxide emissions annually, hempcrete actually sequesters CO2. According to a recent study, hempcrete can sequester 19 pounds of CO2 per cubic foot, roughly the equivalent of the annual carbon emissions of about three refrigerators.
Watch as the Cannabis Industry Lawyer himself explains the approval of Hempcrete into US building code, and discuss the further reaching implications, such as how will this new insulation compare to the price of traditional insulation? While pricing breakdowns are not yet clear, the spread of hemp products in things such as hemp plastics, batteries, and cosmetics indicate that the market for such innovative materials is certain to grow.
The current US housing crisis faces enormous obstacles, rising interest rates. Hempcrete provides relief with density, thermal mass, and excellent acoustic performance. Hemp used in construction prevents mold growth, has a resistance to heat, and absorbs carbon while being a plant-based, non-toxic alternative to materials used to build homes and businesses. Not to mention the medicinal-use and symptom-relief, from various forms of hemp and cannabis.
That’s why it’s so important to check for any marijuana legalization efforts in your state and VOTE. Get all the information you need to cast your vote November 8th at vote.org.
And check back on the Pipeline Blog for the full update on what measures passed, with analysis on what that means for the future of cannabis!
By Julia Ruiz
Julia Ruiz has worked in the cannabis space for 5 years, including political advocacy with the National Cannabis Industry Association, dispensary management, cannabis start-ups, marketing, and public relations. Julia is an outspoken advocate for safe patient access and policy reform, having been prosecuted for medical cannabis use in a since-legalized state.