“The imperial vastness of late Roman architecture was made possible by the invention of concrete.”
The Oxford scholar who penned this observation accurately described the historical importance of concrete, which underwent major advancements in the centuries that preceded the Roman Empire. Two thousand years later, another major advancement — hempcrete — has the potential to transform architecture once again by making construction significantly more sustainable. Researchers from Pennsylvania State University explain how.
“The materials ability to absorb carbon dioxide makes it an ideal eco-material in lessening the negative environmental impact of the construction sector,” per their 2021 study in the International Journal of Architecture, Engineering and Construction. “It displays good economic value as well as excellent thermal and insulative properties, ensuring comfortable living atmospheres. It holds an excellent lifespan and offers a low maintenance cost.”
For those unfamiliar with hempcrete, this bio-composite material consists of hemp hurd (the short fibers in the plant’s inner woody core) and a lime-based binder. To make bricks, lime and water are added to the hemp straw causing it to grow harder, and the straw is then molded into sturdy bricks that are 7 to 8 times lighter than concrete. As a construction material, hempcrete can be used to make walls, floor slabs, ceiling and roof insulation. The New York Times describes hempcrete as flexible, airtight yet breathable, impervious to mold and pests, fireproof and free from toxins.
In the United States, residential and commercial structures make up about 40 percent of the country’s total energy consumption, which in turn accounts for nearly 38 percent of all carbon dioxide emissions. Hempcrete, like the cultivation of hemp itself, actually absorbs carbon dioxide emissions. In a home built with hempcrete, this means the walls are literally sucking carbon dioxide out of the air. Likewise, hemp bricks naturally trap and redistribute heat, which reduces energy costs for heating or cooling the space. By how much? The researchers suggest hempcrete can potentially reduce heating bills by 50 to 70 percent.
The 2021 study did note one disadvantage — hempcrete is not suitable for load bearing — which means a wood frame or other gravity load-resisting system is required. However, hempcrete grows harder with time, and it’s more flexible and less brittle than concrete. Such flexibility provides added value in earthquake-prone states like California. Plus, hempcrete’s “ability to resist fire, mold, fungus, and moisture along with its carbon-negative properties compensates” for its load-bearing limitations.
As far as the use of the hemp-based building materials, the researchers explained, “Making hempcrete can be straightforward without the need of complicated technologies and processes, from its initial stages of growing to its final stages of constructing. Growing the durable material requires limited use of fertilizers, while offering various construction methods such as in situ, wet-mixed hempcrete pouring, hempcrete bricks and blocks, structurally insulated panels, and spraying hempcrete.”
Availability, cost, training and awareness of hempcrete will influence its rate of growth, but studies like this help increase confidence in and familiarity with the material. The eventual mass production of hemp straw bricks should help reduce cost, and its widespread use will definitely help the environment.