The built environment contributes to over 40% of global greenhouse gas emissions. To change this, construction professionals should aim to reduce the sector's environmental impact while meeting humanity’s needs.
So, where does this big leap to greener construction and buildings start? Could it be with innovative but untested technologies? Improving building codes, a practice that has proven almost impossible to implement? Or could it all start by simply using lower-impact, organic building materials?
Hempcrete has been touted as one such solution. But what the hell is it? In this article, we’ll demystify this cutting-edge material and help you understand how it could end up on your next project.
Could hempcrete replace existing CO₂ offenders?
Over half of all global raw materials consumed are used in the construction of buildings and roads, and the most popular ones have a pretty dirty record - we’re looking at your reinforced concrete! Greenhouse gas emissions associated with these materials arise throughout the extraction, fabrication, construction, and disposal. Compounded together, this process embeds massive amounts of carbon into the material’s footprint and significantly contributes to climate change.
In contrast, the hemp plant is a natural resource that has been used for thousands of years. It was initially spun into textiles and more recently is used in clothing, fabrics, biofuels, animal feed, and even biodegradable plastics. But over the past few years, researchers have found an even more exciting use for it as a construction material! That’s right, hemp, combined with a lime-based binder, is now being used as a composite construction material and has been used in various applications.
Hempcrete’s unique and durable natural properties allow for its use in many building applications, being particularly effective as an insulating material within wall cavities. Hempcrete as an insulator offers an alternative to commonly used fiberglass or polymer-based insulators in walls, roofs, or floors.
Hempcrete can also be used in place of drywall and plaster by directly casting it around primary or secondary structural frames. This allows designers to incorporate its unique thermal performance (high thermal mass) and aesthetic properties whilst also acting as an all-in-one sealant from the elements.
Research is even underway to assess the effectiveness of using hemp-based elements in place of steel rebars in RC construction! This would both cut carbon emissions and address the problem of rebar corrosion that often leads to the premature decay of structures. This would be a pretty crazy game-changer for the sector, but whether or not it’s viable at scale remains to be seen…
When hemp is harvested, its fibers are stripped off, leaving the woody hemp core or stalk behind. After chopping it finely, it is mixed with a lime binder to produce lightweight concrete. This gives hempcrete its modest structural and compressive strength and stiffness. However, for now, its unique properties are primarily suited to non-load-bearing applications as part of timber or other framed buildings in smaller-scale construction.
Whilst it is a very lightweight material, hempcrete has the characteristics of a heavier material that can both insulate and store heat. By varying the mixed quantities, hemp-lime materials can be used in denser or lighter composites for insulation due to their remarkable thermal and acoustic performance. This is what gives it its versatility.
How people experience a building, feeling hot, cold, or just right, is a measure of a building’s thermal comfort. Hempcrete’s high thermal mass and insulation, thermal inertia, and air-tightness structure can play a significant role in how one experiences their home. This means that not only can hempcrete replace structural elements, but it can also be an effective tool for MEP engineers too.
And the kicker? It’s great for the environment as well! We’ll get into that next…
Hempcrete comes with considerable sustainability credentials. During its rapid growth cycle, hemp absorbs carbon dioxide, and even during construction, hempcrete is actively capturing and storing CO₂ in the structure.
Growing hemp, in general, helps in the process of regenerating agriculture and replenishing the soil. The energy and water used in planting, harvesting, and processing hemp are low. In addition, the low-value parts of the hemp plant (the woody hemp core or hemp shiv) are required to make hempcrete. So, the hemp leaf itself can still be used for other applications. Thereby hempcrete replaces many quarried materials as an aggregate. Compared to traditional aggregates like stone and gravel, the environmental impacts of hempcrete aggregate extraction are negligible.
As we saw above, as an insulator, hempcrete can also replace more common synthetic fossil fuel-based materials, which consume a lot of energy and emit toxic chemicals during manufacture. As a structural finish to internal surfaces, hempcrete can regulate humidity, helping to eliminate toxic mould growth; it can insulate and store heat, creating comfortable and healthy interior environments.
A path to greener construction
While hempcrete has so far been used primarily in residential applications, there are a few innovative examples of hempcrete being used in commercial settings.
European countries have more readily adopted hempcrete construction in buildings for several decades; the uptake has been slower in countries like the United States and Australia. However, hempcrete is a strong contender for mass adoption as industries look for sustainable and practical alternatives that can cut embodied carbon.
In 2021, Lemoal Lemoal Architects completed France’s first public building made of hemp, the 4,000-square-foot Pierre Chevet Sports Centre. This was an opportunity to test the limits of what can be achieved with hemp and be at the forefront of something new. The walls of the sports center are infilled with hempcrete blocks clad in cement-fiber panels to protect them from the elements. Pierre Chevet Sports Centre (de zeen) On the other side of the pond, Canadian startup Just BioFiber has created a modular building system based on structural blocks that, according to the company, can ‘outperform virtually all existing and alternative buildings’. The cores of these structural blocks are made from hempcrete without portland cement, all encased within load-bearing blocks. Industrial hemp and lime binder have been integrated into pioneering structural solutions that advance visions of sustainability, resilience, longevity, functionality, and healthy living. The ‘Harmless Home’ with Just BioFiber’s blocks for the exterior walls (Just Biofiber)
Opportunities to minimize transport emissions, reduce embodied carbon, unlock sustainable design, and contribute to local economies are some of the reasons why CalcTree loves hemp. It blazes the way forward to more innovative and sustainable products in the construction industry.
Where do we go from here?
A quick dive into the web helped us find a few up-and-coming start-ups occupying the innovation space in material technology. We’ve chosen two that are currently developing hempcrete solutions and technologies:
In the United States, Hempitecture produced hemp-based solutions and materials specifically for the building and construction sector. Its mission is to integrate hemp-based products into our built environments, positively impacting people and the planet by reducing emissions and regenerating farmland.
An Australian, female-owned hempcrete construction start-up that works with licensed hemp farmers to convert what are usually hemp waste products into saleable materials, focusing on building materials and much more!
💬 “Engineers have three books: wood, concrete, and steel. That’s it.”
-Terry Brooks, vice-president of Just BioFiber
Alongside developments in hempcrete, recent studies have been advancing research in supplementary cementitious materials (SCM) to reduce the carbon footprint of one of the industry’s biggest CO₂ offenders: Portland Cement. The use of virgin aggregates or waste materials has been experimented with, but the research is patchy and still pretty immature. In any case, advances in engineering techniques, design, and innovations will have to keep pace with breakthroughs in alternative sustainable materials.
-  Ip, Kenneth & Miller, Andrew, (2012). “Life cycle greenhouse gas emissions of hemp–lime wall constructions in the UK”. Resources, conservation, and recycling, 69, pp.1–9.