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Hempcrete 101

The Sustainable Building Revolution

Hemcrete 101


There is a lot of discussion about slowing down and reversing the contamination of our planet. In order to do this we need sustainable tools in every aspect of daily life. Hempcrete is a valuable tool that can be used to make our buildings more environmentally friendly. We usually think about daily living in terms of the products we use: shopping bags, food containers, automobiles, and recyclables. But we usually miss the environment that’s closest to us — our homes and the buildings we spend our time in.

We usually miss the environment that’s closest to us — our homes and the buildings we spend time in.

Let’s take a look at hempcrete, one of the new green building tools in our tool-belt that can have a beneficial daily impact on us in the short-term, as well as providing a long-term boost in sustainability on the surface of our planet.

What can we learn about Hempcrete?

This article will explain:

  • What Hempcrete is
  • How Hempcrete is used
  • Why use Hempcrete to build homes and buildings.

What is Hempcrete?

Hempcrete is a material used in construction made from the hemp plant, lime, and water.

Before you start imagining psychoactive leaves and flowers in your walls, hempcrete uses the stalk of the hemp plant made up of the inner core and sometimes a small amount of the long fibers. The fibers provide strength to the mixture. The chopped up inner core, or hurds, provide bulk and insulation properties. It has similarities to concrete but also some differences in it’s use and application process.

This mixture is applied in wall forms, between and around the framework, sprayed into roofs for insulation, as a plaster finish, or in pre-molded and cured blocks.

Industrial hemp enthusiasts, manufacturers and potential manufacturers have been experimenting and testing various recipes to find the balance between hemp and binder that provides the greatest strength : insulative properties ratio for construction.

Hemp vs Cannabis

The plant taxonomy of cannabis

Marijuana vs Cannabis labeling

I don’t like to use the word marijuana for psychoactive cannabis due to it’s negative history as a label used to denigrate certain populations. I use the word cannabis to refer to all cultivars and uses of the plant and hemp to refer specifically to industrial uses, even though it is also part of the cannabis plant.

There is a lot of controversy about what is hemp, cannabis, marijuana, CBD, etc. Almost every article or post starts out with an explanation about the differences between them or even an introductory article by itself, to help clear away the cobwebs of confusion.

Plant comparison and cultivars

Cannabis Sativa whose closest relative is hops (used for making beer), is not a large family as far as plant genuses go. The word sativa, from the latin sativus or sativum, in plant taxonomy, means cultivated. This adjective is often given to and associated with plants that give good health or are domestically cultivated. Cannabis Sativa has been cultivated for thousands of years.

In most of the times and cultures in which we have some records, cannabis was considered a single plant but with different uses. Because of the legal judgments against cannabis in the past 100 years there is a lot of confusion about it, what to call it, what we use it for, etc.

I like to compare the mint family to cannabis in understanding the differences between industrial hemp and THC laden cannabis. If you look at a list of plants in the Lamiaceae (mint) family, you will find not just peppermint and spearmint, but also basil, oregano and marjoram. While all of these are spices, they don’t all have the same aroma, properties, or uses.

Indoor cannabis grow operation

Shout out to trailblazin from Pixabay for this picture of an indoor grow operation

In the cannabis family it is the same. Psychoactive cannabis is derived from the flowers, and sometimes upper leaves attached to the flowers, of cultivars that have a high level of the active constituent THCA. When this chemical is subjected to high heat for a period of time it changes into THC, which is how you can get “high” or experience other health effects when smoking or consuming it.

In order to achieve the highest levels of this chemical constituent, not only are specific cultivars and hybrids chosen, they must also be grown under certain special conditions, usually indoors. These plants are pampered and babied to produce a harvest that to growers, feels like their own offspring. It is their pride and joy and requires a lot of work. THC cultivars are usually not grown more than six feet tall.

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On the other hand, the industrial hemp cannabis sativa uses different cultivars that don’t produce THC in any measurable quantity (less than .3%). These plants are also sown outdoors in rows just like corn or potatoes. They are planted rather close together because the desired product isn’t the leaves or flowers (unless they are being grown for seed), but the stalk. Close planting reduces leaves and forces the plant to grow taller to reach the sunlight. These stalks are often harvested when they reach 15 feet or more. This height creates long fibers from the bast of the plant and a strong core that can be chopped up for multiple uses.

hemp fiber harvest Hanffaser Uckermark Pixabay 1280

Thank you to Hanffaser Uckermark at Pixabay for this picture of a hemp harvest

Stems of plants grown for THC can also be chopped up and used for hurds, but due to the regulations and requirements for disposal, they are often wasted. They don’t have a measurable amount of THC or maybe none at all, but most states require tracking of every part of the plant from seed⇢ to harvest, ⇢to manufacture,⇢ to waste.

How is Hempcrete Used?

The most common way hempcrete is used is between structural framework replacing insulation and drywall. This can take on either the form of a built-up wall or by using pre-formed/pre-cured blocks that look similar to concrete blocks. It can replace concrete in above-ground applications, however because it is a natural material that breathes both air and moisture, it cannot be used for the foundation or basement.

It is also used as a type of plaster or stucco to add insulation and a natural finish to walls, both interior and exterior. A sprayed in application can also be applied similar to other roofing insulation. Different applications require different recipes and ratios of hemp-lime-water. Let’s take a look at some of these applications in a little more detail.

Hempcrete Applications:


While there is an insulation product made from hemp similar to traditional insulation bats such as fiberglass, wool, and cotton and others, these are usually applied to retrofit existing structures made without hemp walls. Hempcrete incorporated into the wall’s structure between the load-bearing studs, offers superior insulating qualities making traditional insulation unnecessary. It can also be used to retrofit existing structures as an extra insulating layer, although it may reduce the size of rooms when added to the interior.

Unlike typical insulating materials there are three ways it offers insulation. First it traps air within it’s structure, the way we think of in most insulating materials like fiberglass. The second way is through thermal mass, storing and releasing hot or cool air the same way a log cabin or cob structure would slowing temperature changes. Finally, it also stores and releases water vapor regulating humidity, which in turn affects temperature.

No other insulating materials offer this 1-2-3 combo.


Hemp is an excellent material for soundproofing a room when used on interior walls. It can also reduce noise between floors when used in sub-flooring. The acoustical performance of hempcrete has been shown to reduce exterior noise by up to 50%.

Wall Surfaces

Not only is hempcrete used as the filler between the load-bearing structures of a wall, using an alternate “recipe” can turn it into a wall finish. A plaster or stucco finish using hemp can be applied to both internal and external walls. This gives an “old world” quality to the structure. If paint is desired, a special paint that can breathe rather than seal the wall may be necessary.

Vinyl or other siding styles can also be attached to a hemp wall. A special film that is air and water permeable needs to be applied before the final siding is placed.

Humidity Regulation

Because hemp regulates humidity, it prevents mold and mildew formation. This makes it an excellent material to use in bathrooms or other rooms that tend to have high humidity. Thinner hemp wall-boards can also be used in the interior of basements (although not for the structural part due to it being underground.) While this isn’t necessary as a general rule, they could help regulate the humidity in the basement, as well as offer some sound-proofing, especially if it’s being used to add additional living areas to the home.

The Benefits of Building With Hempcrete

We have looked at what hempcrete is and how it’s used in construction, now let’s look at why we should use it to build our homes and other structures.

Lower Energy Costs

With hemp’s temperature and humidity regulating properties, our need for heating and cooling power is lowered. As an added bonus, the thermal mass it contains helps keep the temperature more even, needing fewer adjustments. It also reduces or eliminates the need for humidifiers and dehumidifiers, another source of electrical usage.

Oldest hemp house built in Japan in 1698

These structures have also shown to have good longevity. Renovations and replacements on less robust materials can cost additional energy long-term. Hempcrete can last hundreds of years. The oldest known hemp house is in Japan and was built in 1698, more than 300 years ago!

Because hemp is naturally pest resistant, it doesn’t require toxic pesticides in the growing environment. Unlike many building materials hempcrete is non-toxic, reducing or eliminating the need for energy intensive air purification systems. There have also been reports of less allergy problems within a hemp structure, potentially reducing the need and cost of allergy medications.

Mold and Mildew Resistant

One of the most expensive problems to fix in a home is black mold. Mold and mildew in humid areas is unsightly and can also contribute to allergy and respiratory issues.

With hemp’s natural ability to regulate humidity and it’s mold and mildew resistance, it is an excellent material to use in reducing or eliminating the threat of toxic mold. Hemp is breathable and allows moisture to pass through without affecting its structural integrity. This prevents the moisture build-up that leads to mold and mildew. The fibers and hurds are not a suitable food source for mold.

Mold thrives in acidic environments, so the naturally alkaline lime binder used in making hempcrete also discourages mold growth. The lime absorbs carbon dioxide while it hardens and cures which increases the alkalinity even more. The oils in hemp fibers have small concentrations of antimicrobial properties that may offer additional mold and mildew resistance.

Pest Resistant

Hemp is naturally pest resistant even in the growing stages, which need no toxic pesticides. In addition, only the fibers and inner core are used, which doesn’t have any organic food source that pests such as termites like to feed on. The alkalinity of the lime used to bind the hempcrete deters pests from burrowing or nesting in the material.

Hemp is compacted during installation, this density makes it less penetrable by pests. The moisture breathability also impacts pests as many of these insects need a sustained high-moisture environment in order to live. Hempcrete is not susceptible to the decay, rot, and fungal growth which attracts many pests.

Hempcrete Building

Fire Resistant

Hempcrete is naturally fire resistant in a few ways.

Hemp is not readily flammable

The fibers and hurds of the hemp plant do not catch fire easily and do not emit toxic fumes when they do.

Lime is fire-retardant

Lime, the binder in hempcrete, is a mineral that requires a high heat to reach its melting point (around 1500℉). In fact, rather than melting, it undergoes a chemical transformation and decomposes. It releases relatively little heat when it does reach this point which can also slow the spread of flames.

Hempcrete is dense

When hemp and lime are mixed with water and compacted to make hempcrete, it becomes a very dense material. It is less porous so flames and heat are less able to penetrate it and it burns at a slower rate.

Natural Disaster Resistance

While we have already discussed how hempcrete can provide fire resistance, it has additional benefits in other naturally-occurring events.


Hemp is a natural biodegradable material and cannot spend a sustained amount of time submerged in water, which is why it not used in underground applications. However, because of its mold and mildew resistance and ability to regulate humidity, it handles temporary water situations quite well with little damage, much better than drywall.


Hempcrete strengthens the wood framing it is built around and has some flexibility. Because of this superior flexibility and strength, it actually handles earthquakes better than concrete. It is also lightweight, ⅛ the weight of concrete, and has a low resistance to cracking under movement.


Hemp is good for the environment and a sustainable material for a number of reasons:


Growing hemp uses relatively little water and doesn’t require herbicides or pesticides. This reduces ground water contamination and there is less pressure on the water supply. It grows fast – 70 to 120 days from seed to harvest, allowing multiple crops per year depending on the climate zone. Less acreage is needed for the same amount of raw materials.

Soil Health

Hemp can be planted as a rotation crop helping to break the cycle of disease from the previous crop. Its deep roots also help prevent soil erosion and improves soil structure.


When hemp plants are growing they absorb CO2 from the atmosphere and store it in their plant cells. This CO2 is sequestered in the hempcrete and by extension in your home or building, removing it and keeping it out of the atmosphere.

Because hemp is naturally pest resistant and doesn’t require toxic chemicals, it is non-toxic and the products made from it are only as toxic as any additional materials that may be added to the mixture. The basic recipe is non-toxic. In addition, hempcrete is biodegradable and will break down over time reducing pollution.


Hempcrete is an amazing building material that you can feel good about using in your next building project. Not only is it good for the environment, it’ s also a good solution for families. It provides more comfortable and less toxic living conditions and lower energy costs while offering long-term material stability.

How would you feel about living in a hemp-built home? Let me know in the comments below ⤵

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