There’s a lot of information out there now about hemp construction. Since the recent passing of the 2018 Farm Bill in congress, which legalizes the growing of industrial hemp on a federal level, the hempcrete building technique has gained media attention.
But what do you need to know if you are thinking about your new dream hemp house or hempcrete remodel?
How Hemp is Used in Construction
Many articles in the press have done a good job of explaining the use of hemp in hempcrete walls. This system involves hemp hurd being mixed with lime binder and then loosely packed into forms that are built around the wall framing. This is applicable in both new builds and remodels. There is lots of room to experiment, as well.
For example, the hemp-clay house we worked on uses the hemp portion of the wall solely as an infill which butts up to the inside of the otherwise more conventional wall. It serves as a thermal break and plaster substrate. Hemp can also be mixed into plasters, earthen floors, and used in creating blocks, with either lime or clay binders.
There are companies that make building products made with hemp that could replace plywood, batt insulation, and even wood framing members. For now, though, hempcrete (or hemp-lime, or hemp-clay) is the king of hemp building.
Benefits of Building with Hemp
There are many benefits to building with hemp and hempcrete systems.
First off, the environmental benefits. One way hemp is better than other building materials that it may replace is that its production (farming) and processing (making the hemp plant into hurd) can require less energy, water, and time inputs. In fact, due to its long root system, hemp plants can actually improve soil health by increasing organic matter in soil over time and naturally loosening dense soils.
A hemp home may use less lumber, since the wooden frame of the house can be designed with greater spacing than if the home used more conventional insulating batts that are designed for 16″ or 24″ spaces. And since hemp grows much faster than trees, it requires less water and energy inputs, and a smaller area of land to produce an equivalent amount of material.
Hemp also replaces insulation. Batt insulation like fiberglass and mineral wool are manufactured products that need a lot of energy to create and ship. If local hemp hurd is used instead, the embodied energy is much lower. Also, hemp captures carbon from the air as it grows, which is then sequestered and stored in the walls of your building for as long as it stands. This means you get to start out with a carbon neutral or even carbon negative home from the beginning!
The rise of “sick building syndrome” is well documented. As homes get more energy efficient with tighter envelopes, indoor air quality can decrease. Particularly when the materials used to build and finish them and the products we bring inside are off gassing chemicals and VOCs, this can result in poor health, lowered cognitive abilities, and potential long term disease. In addition, mold can become a problem from condensation forming within wall systems or inside of poorly ventilated homes.
Hemp can help with this is a few ways. If you follow our plaster site, you may have read about how plasters can improve indoor air quality. The lime (or clay) binder in hempcrete is the same earthen material as in a natural plaster. Also, most hemp walls are finished using plaster on the inside.
Also, hemp won’t contribute to VOC and chemical off-gassing as it is a wholly plant based material which has been dried and processed before being mixed with the lime.
Finally, hempcrete walls are highly mold resistant. The lime binder has a very high pH while wet, which prevents mold. And, once it has cured and been plastered, a hempcrete wall regulates humidity and allows water vapor to pass through it in a way that won’t lead to any points of condensation within the wall. There are also no gaps within the wall through which air can move. This eliminates another source of moisture and mold, and contributes to the longevity of your building.
Boosting Local Economies
Growing hemp is seen as a healthier, safer alternative to other economic activities, like mining and large scale industrial agriculture. Because hemp requires less inputs of pesticides and herbicides than other crops like cotton, soy, and corn, it is a good candidate for replacing or joining into a crop rotation with these plants. Also, parts of the country whose economies were dependent on coal mining or manufacturing jobs could use the recent legalization of industrial hemp to carve out a new living. In Colorado, hemp and marijuana growing is already boosting the economy.
Current Challenges of Building with Hemp in Colorado
Since industrial hemp is a new crop in the United States, we are lagging slightly behind in the manufacturing of products using hemp and in the processing of the raw plant material. The equipment, factories, and machinery required for such a task are expensive and it will take time to catch up to other countries where hemp building has been popular for decades.
For example, when we built our hemp-clay project, using a unique and lower carbon version of hempcrete where clay is used to bind the hemp together in the wall instead of lime, we used imported hemp hurd. There are drawbacks to this, like increased embodied energy. However, the current consistency and quality of processed hemp hurd available locally (if it is available at all) meant that there would be more headaches and room for errors than if we bought from a part of the world where hemp building is well established. In those countries, the processing of the plant into the final product is seamless and reliable.
So, while we are still waiting for Colorado and the US to catch up with other areas of the globe, hemp building is coming to Colorado quickly, including in a studio project that we are starting later in 2019. Keep an eye out for updates!