The American Institute of Architects and Architecture 2030 have issued a challenge to the construction industry to reduce its contributions of greenhouse gas emissions to the environment. As part of that initiative, research and development are taking place to reduce the carbon emissions that result from making concrete. In order to strive for sustainability while coping with a high demand for production, there are many creative solutions and disruptive processes being considered. Two of those involve the use of industrial hemp: hempcrete and hemp insulation.

Making hempcrete, also known as hemplime, involves combining processed and chopped industrial hemp stalks with lime and water to create an alternative type of building material that is more similar to drywall than concrete. The fibrous hemp brings flexibility and strength, while removing “embodied carbon.” Research has shown that buildings employing hemp can naturally control humidity, and, like other vegetation, hemp is a carbon sink – it absorbs carbon-containing compounds, resulting in less carbon dioxide released to the atmosphere. Another benefit of hempcrete is that it weighs 75% less than traditional concrete.

Hempcrete is not a structural component, and it does not challenge or replace concrete. Because of its natural tendency to absorb moisture, it should not touch the ground and is not suited for foundations. Despite these cautions, as a construction component, hempcrete has been used in Canada, Europe, Asia, and Africa for decades. As of 2017, hempcrete projects are also being permitted in the U.S.

To achieve necessary strength in a hempcrete wall, for instance, it will be formed around a stud wall. While it works on a small scale, it can be labor intensive. This method of cast-in-place is a good way to learn the process, but it cannot compete with traditional construction methods. If the method is to have a future in the building industry, it will need to be a controlled process, more like modular construction. Factory-produced blocks and panels could be competitive with traditional construction methods.

Then there’s hemp batt insulation, which can contain as much as 92% hemp and 8% polyester fibers, compared to the ratio of 51% plant fibers and 49% plastics and chemicals in typical insulation. Architects now have the option to specify eco-friendly components like this in lieu of petroleum-based batts or sprayed insulation.  

Advocates explain that industrial hemp requires less water to grow compared to other crops, is not as susceptible to insect pests and can produce up to two crops per year, depending on the location of cultivation. As a substitute for timber, it could save millions of trees and has the potential to be locally sourced. While millions of acres of land would be needed to grow industrial hemp for larger scale use, proponents say every aspect of its cultivation and use fights embodied carbon. Research is continuing on developing varieties that will perform well in a variety of USDA hardiness zones.  

There are challenges and obstacles that exist for the use of industrial hemp in construction. But they don’t appear to be insurmountable in the quest for alternatives to petroleum-based building components. As municipalities set goals for sustainability, it could help garner acceptance for these creative solutions, disruptive processes and alternative materials. 

Watch season 4, episode 4 of The AEC Disruptors Podcast to learn more about hempcrete.

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