Q&A: Hempcrete Basics
What is hempcrete insulation?
Hempcrete is an eco-friendly high performance insulation material. It is produced from the woody core of the stem of the hemp plant called the shiv, which is typically disposed of in the hemp fibre harvesting process. The shiv is mixed with a lime binder and water which makes a lightweight but solid insulative material. Hempcrete is airtight but vapor permeable meaning that it blocks air movement but allows water vapour to pass through it. This breathability allows hempcrete to regulate moisture naturally, preventing moisture buildup and mold.
How is hempcrete insulation installed?
Our hempcrete is cast inside temporary wooden forms and lightly tamped to create a solid, insulative wall system. Combined with a natural plaster finish, the hempcrete wall system replaces multiple layers of conventional building materials like vinyl siding, foam board, plywood, batts of insulation, spray foam, drywall, synthetic vapour barriers, plastic membranes, glues, tapes and sealants. When the hempcrete is dried it hardens into a durable and natural insulation material.
Hempcrete insulation blocks
Elm Natural Builders also manufactures hempcrete blocks that eliminate the need for mixing and curing the hempcrete mixture on site. The blocks are laid like conventional bricks and mortared into place with a modified hempcrete mix.
What are the best wall finishes for hempcrete insulation?
Lime plaster is the optimal wall finish on either side of a hempcrete wall because it is cost efficient, beautiful, durable, and retains the vapour open nature of the hempcrete wall. However, other conventional siding and wall coverings may be used with hempcrete provided the appropriate installation details are followed. On the interior, hempcrete can be finished with a lime or clay plaster, or in some cases, remain exposed, depending on the aesthetic of the design. Drywall is not an ideal interior finishing material for hempcrete because it limits vapour diffusion through the wall and is susceptible to mold growth.
Is hempcrete another version of concrete?
No. Hempcrete is also known as hemp lime insulation in Europe. Although its North American name does invoke concrete, the two materials are not interchangeable and are completely different in their composition and environmental impacts. Hempcrete is an insulation material and is not load bearing.
Where do you source your hemp from?
All of our hemp is 100% sourced in Manitoba. We are proud to support the Manitoban industrial hemp industry.
Can I afford hempcrete insulation?
The manufacturing of hempcrete insulation is extremely labor intensive because every batch is mixed and cast manually by our team. Even so, our pricing is on par with synthetic insulation, yet our products do not have any of the harmful environmental and health effects of these carbon emitting products.
What is the history of hempcrete insulation and where in the world is it used?
Hempcrete insulation was first developed in France in the 1980s as a way to add insulation to medieval timber-framed buildings without compromising the original integrity of the structures. Since the 1990’s residential and commercial structures have been insulated with hempcrete in France, the United Kingdom and all over Europe.
The movement spread quickly to North America. Industrial hemp cultivation was legalized in Canada in 1998 and the US followed in 2018. Hempcrete projects started appearing all over the continent, with the current number of structures estimated to be in the hundreds and increasing annually. In 2024, hempcrete was included as an appendix in the 2024 International Residential Code (IRC), which governs U.S. residential building codes, opening the gates for even more hempcrete insulated structures.
World’s tallest hempcrete structure: a 14 story hotel in Capetown, South Africa
A residential hempcrete addition completed by Elm Natural Builders Winnipeg, Manitoba, 2021
Can I legally build with hempcrete insulation in Manitoba?
Yes. In 2018, Elm Natural Builders built their first permit approved residential hempcrete addition. Since then, we have completed multiple additions and new home builds around southern Manitoba including within the City of Winnipeg, Red River Planning District, and South Interlake Planning District. All of our hempcrete projects are fully engineered and permitted within the different planning districts in which we work.
We are part of a movement advocating for the inclusion of hempcrete in the Canadian building code which will speed up the hempcrete permitting process and are hopeful that with the US’s inclusion of hempcrete in their national code that this will happen here in the next few years.
Is hempcrete is a good insulator?
Excellent R-Value
Hempcrete provides excellent R-value for colder climates like Manitoba. R-value measures how well insulation can prevent the movement of heat into and out of the home. Higher R-value means greater insulation performance. Hempcrete has an R-value of 2.4 to 4.8 per inch (depending on density) which is comparable to fiberglass batt, the most used insulation in North America which has an R-value of 3.8 per inch. The advantages of hempcrete are that, unlike fiberglass, it is 100% biodegradable at its end of life cycle, is carbon sequestering, and produces no VOCs over its lifecycle (read more in our “Hempcrete: Good for the Planet page.”)
What is the Thermal Mass and Thermal Lag of hempcrete?
Thermal mass is the ability of a material to absorb, store and release heat over time. Thermal lag is the rate at which a material releases the stored heat. Typically, the higher the thermal mass, the longer the thermal lag. Hempcrete provides high thermal mass and long thermal lag thanks to the density of the lime binder once it sets into the hempcrete mixture. This effect allows hempcrete to store heat within the mass of the material itself, and release it over time, as the internal temperature of the house cools down. This affects the way a hempcrete house works in two ways:
First, since heat is stored in the fabric of the structure as opposed to the air contained in the rooms, natural ventilation is possible. Cracking open a window, even during cold weather does not mean losing all the heat in the space, since the heat stored in the hempcrete will slowly radiate to the room as it cools down. This effect means hempcrete homes can be less reliant on complex mechanical ventilation and heat recovery systems to maintain fresh air. You can literally air out your house without losing all the heat.
Secondly, due to the thermal lag effect in the mass, hempcrete buffers temperature changes in the living space, so that a constant comfortable internal temperature is more easily maintained. This allows for heating and cooling systems to be smaller in a hempcrete house as opposed to a conventionally built house, saving cost and saving energy.