Homes built from hemp in Britain: why you might want one too

Surrounded by green fields, Flat House, located on a farm in Cambridgeshire (UK), looks like a typical converted barn. But inside the building, you immediately realize that this is something completely different. What is special about this house, the publication said with the BBC.

Photo: IStock

“The walls remind me of the hay bale holes we used to make as kids,” says Flat House owner Gemma Barron. — The house has excellent acoustics. And last year we turned off the heat for 24 hours in the middle of winter and it was warm inside.”

What makes this bright, airy and cozy home extraordinary is the material it is built from: hemp. While we are more familiar with the cannabis plant's association with the psychoactive substance and its use in dietary supplements and textiles, hemp is fast becoming a sought-after building material.

The fast-growing plant is a renewable resource with carbon sequestering properties. When used in construction, it usually takes the form of "hemp concrete", known as lime-hemp concrete. It is a durable material made by mixing hemp brome—the woody core of the plant—with a binder of water and lime. Hempcrete has a high thermal capacity, making it an ideal insulation material that improves the energy efficiency of buildings and reduces greenhouse gas emissions over time. It continues to absorb carbon throughout its life.

Sustainable materials are in high demand as the construction industry moves towards decarbonisation. Buildings and structures account for approximately 37% of global energy and process-related carbon dioxide (CO2) emissions. This is due to the industry's heavy reliance on fossil fuels, including carbon-intensive materials such as concrete, steel and glass, as well as greenhouse gas emissions from heating and cooling our buildings.

With its carbon sequestering properties, hemp has the potential to help countries reach zero and make building greener.

On the subject: How different ways of using cannabis affect the body: benefits and harms

“Optimizing how we design, build and renovate our buildings is critical to reducing emissions and enabling the UK to meet its climate targets,” says Yetunde Abdul, head of climate action at the UK Green Building Council. “An important part of the solution includes exploring the use of natural, low-carbon alternatives to vital building materials, such as hemp concrete or timber.”

According to the European Commission, one hectare (2,5 acres) of hemp sequesters between 9 and 15 tons of CO2 and takes only five months to grow, meaning it is better than commercial forestry at sequestering carbon. Moreover, hemp cultivation is reported to help regenerate the soil and remove heavy metals from it.

But there are a number of challenges that need to be overcome before hemp can make its mark on the construction industry. These include changes in government regulation, technical certification, and the funding and infrastructure needed to expand commercial cannabis production, streamline supply chains, and make it more accessible to use.

Industry development

Today, the hemp industry is being developed primarily by environmental architects in Europe and North America, largely due to the regulations governing hemp growing in these regions. It is worth noting that the industrial version of the plant does not contain the psychoactive substances of conventional cannabis.

Hemp concrete, or hempcrete, doesn't work like regular concrete; this concrete cannot be used structurally, so it must be combined with load-bearing materials such as wood or stone. But as insulation, it offers a less carbon-intensive option than petrochemical-based materials like fiberglass and foam.

Hempcrete “does it all,” says Summer Islam, co-founder of London-based Material Cultures, the research and design studio that built Flat House in 2020.

“Its high thermal mass means that it slowly regulates its internal temperature, warming up and releasing heat,” explains the co-founder of the London-based studio.

It is hygroscopic, Islam clarifies, so it absorbs and releases moisture, making it a good tool for fighting mold in buildings.

The hemp used for Flat House was grown on the surrounding lands of Margent Farm. The project represents what Material Cultures calls “circular ecology,” an approach to building in which buildings emerge from the landscape and can naturally reintegrate into it. Hempcrete was used in prefabricated panels to create the walls of the house, anchored around a timber structure. Inside the house, materials remain exposed.

One of the disadvantages of hemp concrete is that it deteriorates when exposed to rainy weather, so Material Cultures needed to find a new solution for the Flat House's exterior while still utilizing the plant's full potential. Instead of hemp skins, the building is upholstered with bast fiber, which is already used commercially to replace fiberglass in the aerospace and automotive industries.

Material Cultures heat-pressed these hemp fibers with natural sugar-based resin to create rain-resistant cladding panels that cover the home. The farm continues to produce these panels, which is of great interest to other architects who want to use this material.

Material Cultures plans to continue using hemp at the new Phoenix Project in Lewes, East Sussex. Designed by Human Nature and conceived as a 700-home sustainable neighborhood, the project will use hemp concrete along with locally sourced wood in most of the buildings.

Hempcrete is not a new invention; it has been used in buildings for thousands of years. However, more modern building materials have emerged in the last century, and the criminalization of hemp cultivation due to its association with recreational use of cannabis has only helped develop the new industry.

On the example of France

In France, the cultivation of hemp has never been prohibited by law, and this has contributed to the fact that the country has become one of the world leaders in the production of industrial hemp. Since the modern revival of hemp concrete at the end of the XNUMXth century, a number of building projects have been built around the country using this material.

In 2020, a seven-story social housing block was completed in Paris, which used hemp concrete as the main insulating material, as well as a wooden frame. The architectural firm behind the project, Barrault Pressacco, had used hemp concrete sporadically over the previous decade, but this was the largest use of the material.

Thibaut Barraud describes hemp concrete as "architecturally virtuous" praising its thermal performance, breathability, feel-good effects and carbon sequestration.

"There is no single solution to save the world"

However, this is not a perfect solution: “Hemp is great, but lime is a problem,” he says. Lime production requires limestone to be heated to about 1000°C (1832°F), which releases carbon.

“There is no single solution to save the world,” Barro says. “But for now, hemp concrete remains the best option. It is being used in a large residential and commercial building currently under construction in Paris. The company is investigating whether hemp concrete can be used in retrofit projects. Retrofitting has become a vital way to improve the energy efficiency of buildings without the huge cost of carbon emissions and demolition waste.”

To date, hemp concrete has mostly been applied in small residential projects due to supply chain, scaling, and cost issues.

“The UK's facilities are not yet equipped for large-scale production,” says Islam. “The equipment for it is very expensive and is not distributed throughout the country.”

According to her, investments are needed - in business, infrastructure, skills and certification of materials. Until that happens, hemp concrete will remain an expensive and scarce material to work with, exacerbated by high insurance premiums due to being classified as "substandard".

Obstacles

Paloma Gormley, another co-founder of Material Cultures, argues that the "massive investment" of high-carbon material manufacturers in the approval of their products has allowed them to dominate the market in terms of both accessibility and accreditation.

“There is a similar process that needs to happen for materials like hemp concrete.”

Legal regulation, even just for growing cannabis, is another huge hurdle. In the US, for example, the industrial cultivation of hemp was illegal until 2018, as the plant was considered a controlled substance. Directly hemp concrete was only approved for use in the country's housing building code in 2022; he remains banned from commercial projects until at least 2025.

In South Africa, hemp was finally recognized as a crop in 2021, allowing it to be grown in the country. Cape Town-based Wolf + Wolf Architects has made a name for itself in hemp architecture over the past 15 years, but until recently it had to rely on plant imports.

“I started working on my first hemp home in 2007,” says founder and principal of Wolf + Wolf Architects. “I was fascinated by all of its use cases and saw the positive impact they could have on decarbonizing the built environment.”

His company is currently completing a prefabricated high-rise building in Cape Town using hemp concrete, which is said to be the tallest building in the world built using this material.

This architecture firm is currently working on four more hemp houses and has begun designing another tall building using the same technology. The founder and CEO of Wolf + Wolf Architects is optimistic: “Interest in hemp as a building material is growing exponentially in South Africa. This is the start of a whole new industry in the country.”

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With a growing understanding of the material's many benefits, the use of hemp concrete is on the rise, although it is concentrated primarily in Europe and North America. The European Commission has reported that the area of ​​land in the EU devoted to industrial hemp cultivation increased by 75% between 2015 and 2019, with France accounting for 70% of the total production.

While other countries are slower to use hemp as an agricultural product and building material, things may soon accelerate. In November 2022, the UN published a report on the benefits of industrial hemp. The international organization said that in order to fully exploit the potential of cannabis, countries need to clarify the legal status, resist the limitations of the regulatory framework and cooperate at the regional level to promote the creation of production chains.

Material Cultures believes that the use of sustainable building materials such as hemp can be part of the transition to a building approach that uses local natural resources.

“This includes getting most of your building mass from fast-rotating crops as a way to provide low-carbon insulation, as well as carbon capture and storage in buildings,” says Gormley.

Although what the environment really needs is a drastic reduction in construction. When you build, according to Islam, it is important that you "do it in a resource-saving, economical and thoughtful way." Therefore, the fast growing and carbon absorbing hemp looks like an ideal material to use.

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