‘It’s almost carbon-negative’: how hemp became a surprise building material

(The Guardian, 15 Feb 2024) Proponents of the material tout its non-toxic and mould, fire and infestation-resistant properties.

Cannabis sativa, the plant of the thousand and one molecules, has a long and expansive reputation – as a folk medicine, a source of textile fibre for clothes, for making rope or plugging holes in ships.

But now cannabis – or specifically its non-psychoactive variant, hemp – is being touted for something greater still: building blocks for housing that may avoid some of the environmental, logistic and economic downsides of concrete.

The cement industry is responsible for about 8% of planet-warming carbon dioxide emissions, alongside problems created by unyielding surfaces and low insulation, or R-value, properties. The search for large-scale alternatives has so far yielded few results, but on a small scale there are intriguing possibilities, including the use of hemp mixed with lime to create low-carbon, more climate healthy building materials.

“There’s an enormous growth potential in the US for hemp fibre used for building and insulation,” said Kaja Kühl, an urban designer and the founder of youarethecity, a design and building practice based in Brooklyn, New York. “Hemp was only legalised in 2018, but now industrial hemp is following the first wave of CBD and cannabis.”

Last summer, Kühl, who is part of a Columbia University initiative to help apply environmental initiatives to the Hudson Valley, completed two cottages on a farm in upstate New York using the hemp-lime, known commercially as hempcrete, in their construction. The blocks are not load-bearing, so the material is used primarily for thermally efficient insulation and interior walls.

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The Guardian, 15 Feb 2024: ‘It’s almost carbon-negative’: how hemp became a surprise building material