Hempcrete: An Alternative Sustainable Construction Material

By Sebastian Rogalski

Source: Sebastian Rogalski


The built environment industry is one of the largest primary energy consumers and significantly contributes to atmospheric emissions. The industry in South Africa accounts for roughly 40% of all energy consumption in the economy. Transportation, hoisting and construction materials are the largest consumers in the construction process. With the built environment industry being a large factor in further development and a significant contributor to atmospheric emissions, the goal to ensure that this industry of further development strives for sustainability is a priority.

The industry must minimize energy consumption and meet the increasing demand for sustainable and environmentally friendly construction materials. The choice of a construction material plays a significant role in reducing the impacts of the industry. The more efficient the buildings are, the materials used are of greater importance in terms of total energy consumed. The use of construction materials with good thermal properties as an alternative to conventional construction materials with poor thermal properties will aid in the further development of sustainable buildings and will reduce carbon emissions. New innovative thinking and design approaches are being investigated to reduce these emissions. More attention is being focussed on using a plant-based biomaterial such as hempcrete as an alternative construction material which will offer sustainable solutions to the built environment industry and aid in achieving sustainability goals.

What is Hempcrete?

Hempcrete can be defined as a breathable hygroscopic non-load bearing material comprised of hemp hurds, a binder and water. Hempcrete has a low-medium density, excellent thermal properties, a total negative CO2emission, good hygric properties, high acoustic absorption and resistance to fire. The above-mentioned characteristics lead to improved energy and indoor performance of a building.

Hempcrete is formed by mixing water with a combination of hemp hurd and binder in various proportions. The mix design of hempcrete will differ according to the required application. Less binder is used to achieve a lower mechanical property (roof insulation), a moderate amount of binder is used to achieve good mechanical properties (wall application), and the highest amount of binder is used to achieve high mechanical properties (floor application). Hempcrete can be produced in three different methods. It can be produced by spraying, prefabrication and moulding. Each method has its pros and cons, with moulding having a long drying time, spraying being expensive and prefabrication being the fastest, but requires large production facilities.

Why is Hempcrete Important?

The materials used in the built environment industry tend to have a high encapsulated energy. The production of these materials often have multiple production stages and thus result in high encapsulated energy. With an increase in encapsulated energy, it can be expected that an increase in emissions occurs. Concrete, often used as a construction material, has a high encapsulated energy and is responsible for a significant amount of carbon dioxide emissions. Concrete accounts for approximately 5% of all the carbon dioxide emissions caused by humans. An alternative sustainable construction material needs to be implemented.

Hempcrete is a hygroscopic material characterized by its ability to readily attract and hold water molecules from their surroundings, either by absorption or by adsorption. This material property will aid in the humidity control of the surrounding environment. If there’s an increase in the room temperature, the relative humidity will decrease, which allows the material to absorb moisture from the air. The opposite occurs when the temperature decreases and the hygroscopic material will desorb moisture, increasing the surrounding relative humidity. This process allows hempcrete to improve the indoor air quality and human comfort of a building. This gives hempcrete its ability to be an excellent thermal insulator.

Since hempcrete comprises hemp hurd, a plant-based biomaterial, hempcrete enables the industry to harness the beneficial natural properties developed over time in nature to achieve specific performance characteristics. A plant-based biomaterial will store and capture atmospheric CO2 through photosynthesis. Unlike conventional construction materials, which require multiple production phases to achieve specific properties, plant-based biomaterials naturally provide these properties without undergoing multiple production phases. This reduction in phase production ensures that a plant-based biomaterial has a low encapsulated energy. This gives hempcrete its ability to achieve a total negative CO2 emission over its life cycle.

Hemp, the critical ingredient of hempcrete, is grown from the cannabis Sativa plant cultivated globally. The cultivation of hemp has excellent economic value for farmers with ease of growing, a crop yield of approximately 21 tons per hectare per year, and a consistent, sustainable supply of raw construction material for the built environment industry and other industries. The plant is good for crop rotation since it grows speedy and does not require pesticides or chemical fertilizers. The cultivation of hemp is well suited to the South African climate.

In Closing

Adopting a sustainable construction material will reduce construction costs, ensure that environmental planning policies are adhered to and conserve our human legacy. Sustainable construction materials comprise renewable resources and have low environmental impacts. Construction materials that exhibit good thermal and hygrometric properties are primarily plant-based biomaterials and can be used in construction. These plant-based biomaterials can replace conventional aggregates in non-load-bearing concrete mixtures.

Thank you, Seb, for your guest appearance this time! We hope to explore more on hemp buildings with you in the near future. Just to add to this wonderful blog post, here you can look at some real examples and more about the author below.

Examples of Hempcrete Buildings

TM joined forces with Wolf + Wolf Architects, AmaHemp and Hemporium to create a Hempcrete panel in one of our recent projects. The aim was to showcase the fantastic qualities coming from hemp building materials. It was really great to get our hands dirty and to experiment with the raw product by creating our own sampling blocks. Here is the panel.

Source: Sharné Bloem

As most of you already know, in 2019, TM took part in the Solar Decathlon Africa competition in Morocco, and our neighbours, Sunimplant had a fascinating Hempcrete house. They were the only team that did not use mechanical ventilation in the form of an HVAC system. And you guessed it. Most days were MORE THAN 40 C! These walls were thick but made an impression.

Source: Sharné Bloem

More about the author

Sebastian Rogalski recently completed his Honours in Civil Engineering. His research investigated the effect a lime-based binder has on the heat transfer through Hempcrete. He found that heat transfer has a direct correlation to the density of the material. For more information on his research, please contact him on LinkedIn.


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