Flat House in Cambridgeshire, UK, looks like a typical barn conversion, but inside, the look and feel is something quite different. “The walls remind me of hay bale dens we used to make as kids,” says Flat House’s owner Gemma Barron. “It has the most lovely acoustic quality. And last year we had the heating off for 24 hours in mid-winter and it stayed warm.”
This comfortable home was built mostly with hemp. This fast-growing plant is a renewable resource, with carbon-capturing properties. When used in building, it typically takes the form of “hempcrete,” a sturdy material made by mixing hemp hurd – the woody core of the plant – with a binder made from water and lime. Hempcrete has both thermal mass and insulating qualities. It also continues to absorb carbon over its lifespan.
Today hempcrete is used mostly by eco-minded architects in Europe and Canada, mainly due to regulations controlling hemp production evolving in these regions. (It’s worth pointing out that the industrial version of the plant does not contain the psychoactive agents of regular cannabis.)
Hempcrete does not work like concrete; it cannot be used structurally and so needs to be combined with load-bearing materials such as timber or stone. But as insulation, it offers a less carbon-intensive option than petrochemical-based materials such as fiberglass and foam board.
Hempcrete “does everything”, says Summer Islam, co-founder of London-based Material Cultures, the research and design studio which built Flat House in 2020. “Its high thermal mass means it heats up and releases heat slowly, regulating interior temperature over the day.” It’s also hydroscopic, she adds, so it absorbs and releases moisture, making it good at regulating mold in buildings.
Hempcrete has been used in prefabricated panel form to create the home’s walls, fitted around a timber structure. Inside the house, the materials are left exposed, with the straw bale-like appearance of the hempcrete visible.
One drawback of hempcrete is that it deteriorates when left exposed to rainy weather, so Material Cultures needed to find a new solution for Flat House’s exterior. Instead of the hemp hurd, the practice turned to the plant’s stringy exterior, known as bast fibers, which are already used on an industrial scale to replace fiberglass in aerospace and car engineering. Material Cultures thermally compressed these hemp fibers with a natural, sugar-based resin to create rain-resistant cladding panels which cover the house.
In France growing hemp was never outlawed, which contributed to the country becoming one of the global leaders in industrial hemp. Following the modern revival of hempcrete in the late 20th Century, a number of building projects using the material have been constructed around the country. Thibaut Barrault describes hempcrete as “architecturally virtuous”, praising its thermal performance, breathability, impacts on wellbeing, and carbon sequestration.
In the US industrial hemp cultivation was illegal until 2018, due to the plant being considered a controlled substance. Hempcrete itself was only approved for the country’s residential building code in 2022; it remains prohibited from commercial projects until at least 2025. In South Africa, hemp was finally designated an agricultural crop in 2021, enabling its cultivation in the country.
Although other countries may be slower to embrace hemp as an agricultural product and building material, things may soon accelerate. In November 2022, the UN published a report outlining the benefits of industrial hemp. The UN advised that to fully exploit hemp’s potential, countries would need to clarify the plant’s legal status, confront the constraints of regulatory frameworks, and cooperate regionally to facilitate the establishment of production chains.
You can read the original article at www.bbc.com