Last Updated: Sep 12, 2024
It's ironic that what might be one of the oldest examples of human industry, dating back to 8,000 BCE in Ancient Mesopotamia, had to deal with some of the most challenging legal constraints in North America from the 1930s until recently. Hemp has long been utilized in many parts of the globe, from China dating back 6,000 years to Europe and the Middle East.
In North America, this rich history of hemp use was marred in 1937. The United States levied a tax on hemp under the Marijuana Tax Act, eventually banning hemp production altogether. Canada followed in 1938 with the Opium and Narcotics Act. Some attribute this to confusion with its twin within the same species – often referred to as marijuana. But unlike marijuana, hemp is classified as not having psychoactive properties. Some attribute this confusion to propaganda spread by the petroleum-based synthetic textile industry that viewed natural hemp fibers as a significant threat to their rise to dominance. Canada reversed this ban in 1998, and the United States followed in 2018. Hemp's popularity is booming as people begin to re-learn the unparalleled diversity of uses of hemp, including food, rope, textiles, wood-like panels, wood oil, and even building insulation. The European Hemp Association has over 10,000 applications for hemp, which proves why our ancestors came to rely on this dynamic plant throughout history.
Hemp is first grown and cultivated in a wide variety of climatic conditions. It's a plant with a fast yield, reaching maturity in 90-120 days. Hemp insulation comes in the form of batts made from the inner fibrous layer of the hemp plant. The insulation can be intertwined with flax, polyester, or kenaf fibers that help act as a binder. Hemp insulation is a dense type of batting that's not as flexible as sheep and mineral wool. Another insulation type made from hemp is hempcrete.
How hemp is grown can be a potential concern. Agriculture methods can vary in their environmental impacts and their ability to regenerate soils or degrade them. Generally, though, hemp requires no pesticides or insecticides. It consumes very little water, which results in a lower environmental footprint to cultivate.
Hemp insulation is often rated at an R-value of 3.5 per inch. The brand, Hempitecture, claims their bats are R-3.7 per inch. You might think that's low compared to polyiso and XPS rigid foam insulation or even spray foam insulation. But these foams lose significant R-value over time, while hemp stays at R-3.5 for its entire service life while also improving the wall assembly's resilience to moisture damage.
You can install hemp insulation in any thickness you need. The batt sizes come standard to fit 2x4 and 2x6 wall cavities for 16 or 24" stud centers. Typical thicknesses available include 3.5, 5.5, and 8 inches. You can stack these on each other if you want to go even thicker.
Hemp insulation can be used in building systems from inner walls, exterior walls, ceilings, and attics. Its higher density allows it to be used as external wall insulation before siding installation. Hemp insulation is not a load-bearing product, so use it accordingly in floor insulation applications. Its vapor permeability is key to its wide array of uses in wall assemblies and adaptability to every type of environment.
Hemp insulation is a durable and resilient product that can last the life of the building.
Hemp's long history is a testament to its sustainability potential. Hemp's lifecycle is very supportive of a planet-friendly status. It's a renewable resource that builds soil and supports a diversity of life within the earth if grown sustainably. Resilient performance during its long lifespan allows it to be used in a wide array of building systems. At the end of its life, it can, and should, be re-used for another application, recycled, or composted, and allowed to decompose back into the soil.
Hemp insulation is non-toxic. It is a plant-based product that contains no VOCs, no chemical binders, and does not off-gas. Hemp insulation is hypoallergenic, repellent to mold, pests, and insects. Compare this to petroleum-based foams that can off-gas or itchy and messy fiberglass insulation.
The cost is usually dependent on the size of the batt. $1.35 to $3.10 per square foot is the current estimated price range.
Hemp insulation is a DIY-friendly installation material. Since its non-toxic, the necessary PPE is minimal, and it does not itch as fiberglass batting can.
Hemp insulation is very dense. You can't just cut it with a utility knife; use a miter saw, circular table, or hand saw to cut it. When you measure, it's better to measure long than short – add ½" to cavity measurement for a snug, friction fit.
You can use insulation hangers or even rope to keep it supported between the framing members before panel installation for overhangs. If you want to stick with the theme, choose hemp twine for this purpose!
Hemp insulation is straightforward to remove after you remove the interior paneling, typically drywall. Even though it's completely non-toxic, it's still recommended to wear essential PPE such as long sleeves, safety glasses, and a dust mask. This step isn't really for the hemp insulation, but for whatever other building material dust could be lurking in an old wall cavity.
Don't disrespect the very nature of hemp itself and send this natural material to a landfill! Recycle it or compost it. You can even use it as a vegetation barrier or weed block in your yard or garden, where it will eventually become plant fertilizer as it breaks down. Or you could think of another innovative use of which there are endless options. Hemp deserves to be returned to where it started its life - in the soil, amongst an incredible diversity of microbes, bacteria, and fungi to return to the earth and feed the next generation of lifeforms.
If possible, source your hemp insulation from the closest manufacturer to reduce the transportation energy footprint.
There are so many benefits that it's necessary to form a list. And, don't be fooled to think the list ends here!
The biggest drawback to hemp insulation is its current lack of availability. It's not yet widely available locally across North America. As a result, it has a higher cost than other types of insulation. But, Rise is working to help with this problem and help it find a home in more North American households - HempWool from Hempitecture is now available on the Rise Store!
It is still more expensive than mineral wool but is cheaper than sheep's wool. While its long-term performance is promising, its R-value is slightly lower than mineral wool or blown-in sheep's wool insulation.
There have been few other plants in history with such a wide array of practical uses that have undergone such limiting legal constraints as industrial hemp. Hemp is an exciting material with so many uses it's almost comical. As building insulation, it rivals its alternatives in overall long-term performance, while it remains at the top of the list in the realm of sustainability. It is just a matter of time before this insulation type is widely available across North America.
Hemp is an excellent example of how sometimes the most novel and exciting building material can be something we discover by looking to the past and learning what our species has been using for millennia. Our ancestors survived; it's wise to learn from them. There are many functional reasons the use of hemp has stood the demanding test of time and has been repeatedly passed down through generations - let's continue the tradition.
Based in Washington State, Tom's education focuses on holistic land management that sustainably grows renewable building materials in a way that replenishes natural systems. His interest is in building systems that combine old techniques and modern science.