"In the United States, the development and adoption of hemp-based construction materials were severely delayed by 20th-century cannabis prohibition. The
Marihuana Tax Act of 1937 placed prohibitive regulations and taxes on all
Cannabis cultivation, effectively halting the domestic industrial hemp supply chain.
[12]
Federal restrictions on the material remained strictly in place until the 21st century. The regulatory landscape shifted fundamentally with the passage of the Agriculture Improvement Act of 2018 (commonly known as the 2018 Farm Bill), signed into law by President Donald Trump.[13] This legislation legally separated industrial hemp (defined as cannabis with a THC concentration of not more than 0.3% on a dry weight basis) from marijuana, removing it from the Controlled Substances Act. This federal legalization opened the domestic agricultural market for hemp cultivation, directly enabling the commercialization and importation of hempcrete materials in the US.[12]"
"Hempcrete is made of the inner woody core of the hemp plant (hemp shives), a lime-based binder, and water.[6] The binder consists of either hydrated lime or natural hydraulic lime.[14] Hydrated lime is made from pure limestone and sets through the absorption of CO2 during the carbonation process.[14] When dealing with time constraints, hydraulic binders are used in combination with regular hydrated lime, because the set time for hempcrete will be less than that of regular limes (e.g., about two weeks to a month, to gain adequate strength).[14]
A small amount of cement, pozzolanic binder or both are added to speed up the setting time.[6] The overall process creates a mixture that will develop into a solid, light, and durable product.[6]"
" Since hempcrete contains a plant-based compound, walls need to be built with a joint in between the wall and ground to prevent capillary rising of water and runoff, blocks need to be installed above ground level and exterior walls should be protected with sand and plasters to avoid rotting shives.[6]"
" In 2022, the US Hemp Building Association submitted documentation to the International Code Council (ICC) to standardize the material. This effort resulted in federal codification; hemp-lime construction was officially approved and published as Appendix BL in the 2024 International Residential Code (IRC).[44]"
Video: https://www.facebook.com/reel/4098082020439967
What is Hempcrete? Everything You Need to Know:
https://www.designsindetail.com/articles/what-is-hempcrete-everything-you-need-to-know
" Cast-on-site hempcrete is installed in a similar way to in-situ concrete. Shuttering is erected and a wet hempcrete mix is either hand poured and lightly tampered down or sprayed in layers. Cast hempcrete panels can also be prefabricated off site to speed up construction."
"Hempcrete's density can significantly increase the thermal mass of timber construction, providing thermal comfort in both winter and summer whilst remaining lightweight enough to avoid excessive structural loads.
Hempcrete is also vapour permeable and hygroscopic, meaning it freely absorbs and releases water vapour. This prevents moisture from becoming trapped within the structure, reducing the risk of damp and rot.
Also, hempcrete is naturally fire and pest resistant, making it a well-rounded material choice for building projects."
"While both concrete and hempcrete can be cast in-situ or laid using precast blocks, hempcrete is non loadbearing (its compressive strength is approximately 17% of concrete) and must be installed between a structural frame.
Think of concrete as a primary, structural material that supports the building and hempcrete is a secondary, infill material used for insulation and thermal mass."
"From a practical perspective, cast-on-site hempcrete has long drying times, typically 6–12 weeks depending on wall thickness and weather. This can extend the overall construction programme."
"In new-build construction, hempcrete is most commonly used to infill and insulate timber framed walls, providing excellent thermal and acoustic performance. It can also be installed within suspended timber floors and pitched roofs, offering a dense yet lightweight and breathable insulation solution."
Building with Hempcrete: Pros, Cons & 6 Project Examples:
https://homegrail.com/building-with-hempcrete/
Includes links to several actual builds.
How to Make Hempcrete - A Step-by-Step Guide:
https://www.architecturecourses.org/sustainability/how-make-hempcrete
