These are the mixtures of hemp and lime – known internationally as hemp-lime – which now gain official recognition in the United States as approved housing insulation material.
One building material who remained on the sidelines for almost a century he dynamically returns to the construction industry, claiming a key role in the sustainable construction of the future.
As quoted in dailygalaxy, the recent decision of the Code International Council to incorporate the manufacture of cannabis-lime into the International Residential Code of 2024 paves the way for the use of the material in single-house and inter-family dwellings in many states of the United States, no longer requiring special urban exceptions or separate mechanical approvals.
This development is considered historical, as until a few years ago industrial cannabis remained essentially excluded from the American market due to federal legislation that did not separate arable cannabis from psychoactive marijuana varieties. The turning point came in 2018, when the new U.S. Agricultural Bill distinctly legalized industrial cannabis, allowing the development of a new market for sustainable materials.
How to create the «green concrete»
The material is produced from the woody inner core of the cannabis plant, which is mixed with lime and water. The result is a light, porous composite material used primarily as insulating wall filling around a wooden frame rather than as a bearing structural element such as conventional concrete.
During the sclerosis process, lime reacts with the carbon dioxide of the atmosphere through carbonization, gradually turning into calcium carbonate – essentially «stone». This natural chemical process allows the material to bind and store coal for decades or even centuries.
The studies show that hemp-lime mixtures offer thermal insulating performance up to 15 times that of conventional concrete, significantly limiting heat losses and contributing to stabilising the interior temperature of buildings.
At the same time, the material features natural «breathing», thanks to the open pore structure that allows the absorption and elimination of water vapor depending on the humidity levels of the environment. This reduces the risk of trapped moisture, mold growth and insect attacks, while the high pH of lime acts as a natural protective.
A building material with a negative carbon footprint
The increasing popularity of this material is directly linked to the effort to limit carbon dioxide emissions in the construction industry, which is responsible for a large proportion of global emissions due to the production of cement, plasterboard and conventional insulation materials.
Industrial cannabis in its development absorbs CO2 through photosynthesis. According to environmental analysis, the quantity of carbon binding the plant may exceed the total emissions generated by the harvesting, processing and transport of the material, thus creating almost a «negative» carbon footprint.
In addition, hemp cultivation requires fewer chemical interventions than other industrial crops, while completing its growth cycle in just 90 to 120 days. The extensive root system also contributes to the stabilization of soil, limiting erosion.
The obstacles that remain
Despite important prospects, the widespread spread of material still faces serious challenges, particularly at infrastructure and supply chain level.
Treatment of cannabis strains requires specialized peeling machines, which remain limited in North America. As a result, many producers are forced to transfer raw material to remote processing facilities, significantly increasing costs.
In fact, several of the first construction projects with this material in the US were based on imported raw materials from Europe, where industrial cannabis was never completely banned and the related know-how developed decades ago.
At the same time, architectural and construction companies invest in new technologies, such as prefabricated cannabis blocks and spray applications, with the aim of reducing the high labor costs required by traditional manual placement of the material on construction sites.
Although it cannot be used on foundations or points with constant contact with wet soil, due to the risk of decay of organic fibers, this material appears to be gaining ground as one of the most promising solutions for the sustainable architecture of the next decade.
