Hemp Structures Could be the Future of Eco-Friendly Building

Finding “planet-positive design solutions”

Did you know hemp-lime homes have existed in the U.S. for over a decade? But not until industrial hemp became legal to grow via the Agricultural Improvement Act of 2018 was there the potential for a U.S. hemp-lime industry.

In October 2022, the International Code Council (ICC) approved hempcrete as an acceptable material for in-fill construction in U.S. homes. 

Manufacturing traditional concrete accounts for 8% of all carbon emissions worldwide. Could hempcrete be a new way forward?

“As the climate crisis deepens, however, the urgency to find planet-positive design solutions is pushing architects to experiment.” – Metropolis Magazine

#DYK Did You Know

• Early uses of hempcrete date back to the Roman Empire when the Gauls used a hempcrete-like material to build a substantial bridge.

• Modern hempcrete was first developed in France in the1980s as a method of adding thermal performance to medieval timber frame buildings. The material has gained popularity in recent years as an eco-friendly solution, as the construction industry grapples with its carbon footprint.

• In the U.S., it was illegal to build homes with hempcrete until 2022, however private individuals have experimented with this building material for over a decade.

What else is important to know about this eco-friendly building material? We’ll break it down for you:

What exactly is “hemp”? 

Hemp is one of the first plants to be cultivated. Archaeologists have found remnants of hemp fabrics from ancient Mesopotamia (now Iran and Iraq) that date back to 8,000 BC.  

Federally legal hemp and cannabis (aka marijuana) belong to the same species - Cannabis sativa. 

Industrial hemp is grown for its high-CBD flower, seeds, fibers, and stem. The concentration of total delta-9 tetrahydrocannabinol (THC), the main psychoactive ingredient, in the flowering tops is equal to or less than the regulated maximum level.

What is “hempcrete”?

Hempcrete is created when you combine hemp stalk hurds & lime binder. 

Hemp hurds are the chopped woody core of the stalks of the hemp plant, stripped of its surrounding hemp fibers. Also known as hemp shiv or shive. It has a similar consistency to wood chips, before being formed into bricks.

Hempcrete is used in construction through its brick form or spray applied by method of mechanical projection of hemp-lime applied onto or into a form using compressed air. Current construction methods often rely on vapor-closed building envelopes that can promote mold and mildew growth, which reduces interior air quality. 

Hemp-lime offers a non-toxic insulation option that resists or prevents mold growth by allowing the free passage of water. This could be important news for people who have mold allergies, are concerned with mold growth, or live in areas with temperature fluctuations. 

It could be a critical option for Appalachia - a region known for a moist climate similar to a tropical rainforest.

How can hempcrete help us reduce our carbon footprint? 

“It can sequester twice as much CO2 from the atmosphere as forests, grows much faster than trees, and requires less space for cultivation,” says Darshil Shah, a materials researcher at Cambridge University in the UK.

Hemp and hempcrete in comparison to building with wood or concrete:

• Grows quickly (50X faster than many trees!) and requires less space to grow.
• Fire resistant.
• A carbon-negative material, meaning the carbon that hemp absorbs as a plant makes up for the carbon emitted during the processing phase of hempcrete.
• Can improve soil quality by extracting toxins and metals from the earth, similar to sunflowers!
• Stores twice as much carbon as most trees.

• Requires less water to manufacture than cement.

• An effective thermal insulator, saving on heating and cooling bills.
• Resists mold and mildew growth due to the alkalinity of the lime
• Absorbs and disperses water vapor (humidity) and softens temperature fluctuations

Any Disadvantages?

In comparison to common masonry, hempcrete takes 10 years to cure. Time can be mitigated with the use of bricks. 

As with most cannabis related sectors, hempcrete remains an expensive building material as the infrastructure is simply, not there. With strength in the material pipelines over the next several years, prices can be expected to reduce. 

Not necessarily a disadvantage, but of note - hempcrete cannot be used as a foundation structure due to its low compressive strength. In most cases, it is not a load-bearing material.

Some could also consider the loose fill method of applying hempcrete via compressed air to be aesthetically unappealing. However, this method provided the most air tight solution as an insulator. 

#DYK Did you know? 

By adding hempcrete as in-fills to historic timber frames and casting, we can repair and upgrade the thermal performance of traditional and historic buildings.

What’s the future of hempcrete?

The new residential hempcrete policy will go into effect starting in 2023.

Submissions to modify the International Building Code (IBC) can be made every three years, and the hempcrete industry will next have an opportunity to propose a change to that code in 2025.

While hempcrete will be available to most home construction projects in the U.S., it remains prohibited from commercial projects, also, until at least 2025. 

Research, testing, and experimentation are essential for making this material cheaper for mass use construction. We hope our roundup can bring more attention to the need for those pathways.

What’s your dreamy hempy house look like? Let us know in the comments.

Written by Lauren Andrews  |  Photo credit: Henrik Pauly via Unsplash