The secret to building more efficient and sustainable houses was in cannabis: hemp

In their search for more sustainable materials and a lower environmental impact, architects have often turned to solutions that are as promising as they are striking. The list is long: concrete made with diapers or masks, glass bricks, blocks made of plastic, tiles and photovoltaic panels or simply a return to wood. To all these solutions is now added another equally promising, equally striking: hemp.

You know: old resources, new uses.

Houses with hemp? Exact. It may come as a shock, but in the construction sector there are people who are convinced that hemp can be a valuable material for building buildings that are more respectful of the environment. And they have not stayed in rhetoric. To demonstrate this, they have developed concrete proposals or even erected buildings. It is commonly used as hempcrete, a special “concrete” that combines hemp with lime and water to be used as a building and insulating material. Other uses are as wool and insulation.

Over the years it has been used to shape constructions that go beyond simple cabins, such as Flat House, in Cambridgeshire (United Kingdom), or Highland Hemp House, in Bellingham (USA). In 2022, the first semi-detached house made of hemp bricks was also presented in Lower Saxony.

But… why use it? For its advantages. At least that is what its defenders maintain, who emphasize that hempcrete is a biocomposite that helps prevent moisture, is breathable, acts as an effective thermal and acoustic insulator, and is resistant to fire. “Its high thermal mass means it warms up and releases heat slowly, regulating the interior temperature throughout the day,” Summer Islam, from Material Cultures, the studio that built Flat House, told the BBC.

“Hemp is an extremely good insulator. It has been recognized to control moisture and provide a cozy living environment. It is flame retardant, making it ideal for Australian conditions and other hot, dry places, such as California,” explains Rachel Burton , from the University of Adelaide.

Are they his only virtues? No. In fact, its defenders place equal or even greater emphasis on another of its advantages: its ability to reduce CO2 emissions, the greenhouse gas that contributes the most to climate change. Shane Chandran, from the company OzHemp, explained to The Property Tribune at the beginning of the year that hempcrete allows carbon to be sequestered and calculated that over its useful life it can remove around 20 tons from the atmosphere.

Calculations by the European Commission (EC) indicate that a single hectare of hemp sequesters between nine and 15 tons of CO2, an amount similar to that of a young forest. Taking into account that the crop takes a little less than half a year to develop, it is a balance that exceeds that of traditional commercial forestry. “Hemp concrete is a carbon sequesterer, since the amount of CO2 stored in the material is greater than the emissions during its production and continues to store carbon during the useful life of the building”, the EC abounds.

Do those numbers matter? Of course. And a lot. As the European Commission itself recalls, the construction sector is responsible for 36% of greenhouse gas emissions. His calculations are in line with those of the UN Environment Program, which estimates that in 2021 CO2 emissions from “building operations” will reach an all-time high of around 10 GtCO2. If the gases emitted during the manufacture of materials such as concrete, steel, aluminum, glass or bricks are added, buildings represent about 37% of global emissions.

“Improving energy efficiency in the construction sector will play a key role in achieving carbon neutrality by 2050, a goal set out in the European Green Pact. Hemp can play an important role in achieving that goal,” stress the community authorities.

But… Are they all advantages? No. As a construction material, hemp also presents some weaknesses and challenges. Hempcrete, for example, is light, but it does not usually have a structural use. In practice, this means that builders must combine it in their projects with other load-bearing materials, such as wood or stone. The “concrete” itself incorporates less respectful compounds than hemp. “It’s great, but the whitewash is still something that should be questioned,” recalls Practice’s Thibaut Barrault. After all, during its production process, carbon dioxide is also emitted.

Those responsible for the Hemp Tiny House project also point to other handicaps: a higher cost for labor, materials and training, availability and drying time. One of the biggest challenges, however, is of a very different nature: legal. As the BBC recalls, in the US the cultivation of industrial hemp was restricted until 2018 due to the consideration given to the plant and its concrete was not approved for the country’s residential construction code until 2022. For its appearance in the International Construction Code (IBC), fundamental in commercial buildings, will have to wait yet.

Is there work pending? Yes. And not only on a technical level. In 2022, the UN recognized that, although industrial hemp does not have toxic properties, it remains “a controversial plant”: “It is often mistakenly associated with its use as an intoxicant. A negative connotation still prevails, which is partly due to the confusion about the botanical characteristics and the chemotype of the plant”.

The agency even goes further and insists: if we want to “take full advantage of the potential of industrial hemp” countries must get down to work. “A clarification of the legal status of hemp, differentiating it from the toxic substances in cannabis, could be the first step taken by governments,” he underlines.

And what exactly is hemp? A crop that has gained surface area in the EU over the last few years to reach 34,960 hectares in 2019 and that has industrial applications that go beyond construction, such as in the textile, food and feed processing or production sectors. of paper.

Hemp is a species of the Cannabaceae family with a very low level of tetrahydrocannabinol (THC), the main psychoactive constituent of cannabis. In the EU catalog there are 75 different varieties registered and its cultivation is directed mainly to industrial uses. Given its low THC level, hemp that complies with the provisions of the CAP is not used to make narcotic drugs.

Images: Wikipedia and Tomline43 (Flickr)

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