Picture credit: Joel Muniz on Unsplash

A substance deemed to be almost carbon negative is the surprising material that’s starting to be used more widely in construction. Created from the Cannabis sativa plant, the hemp-lime market is projected to grow at 16% a year between 2021 and 2028. And the overall market for green building materials is expected to hit £332bn by 2026.

With the cement industry contributing to 8% of all carbon emissions, it makes sense to champion building materials that have a lesser impact on the planet. Hemp-lime, also known commercially as Hempcrete (although it contains no concrete) is created from the non-psychoactive version of the cannabis plant.

It’s made by mixing hemp shiv – the woody stem of the hemp plant – with a binder which is either pure lime, or lime mixed with a smaller proportion of Portland cement.

Used to create non-load bearing blocks, hemp-lime is typically used for thermally-efficient insulation and interior walls. It has already been used in the UK, in a Passivhaus development of five homes near Newmarket in Suffolk. Hemp, from the company Hemspan, was used as the primary insulation material in the development’s barn-style abodes.

Another high-profile project that’s using the material is a housing project for displaced people and war orphans in Lviv, Ukraine. Tao Climate, a company using the latest technology to grow hemp at scale, is partnering with Ukraine’s Hemp Technology to use Hempcrete in this development.

The Lviv project is a finalist in Elon Musk’s XPRIZE for carbon removal, and it has been estimated that it will sequester more than 1,000 tonnes of carbon dioxide. Hemp can capture up to 15 tonnes of CO₂ per hectare, per year via photosynthesis. If 25% of the world’s agricultural land that’s currently used for livestock and dairy was devoted to growing hemp, this would close the UN emissions gap of 23 gigatons of CO₂ annually. That’s the amount needed to halt global warming at 1.5 degrees above pre-industrial levels.

Hemp-lime usage is taking off in the US too, with hemp cultivation having been legalised in 2018. However one challenge is that much of the original knowledge of hemp and its properties has been lost. It was originally outlawed in the US in 1937, along with marijuana. The market is being restarted, but people are learning how to use this material from scratch.

Aside from the carbon-sequestering benefits, hemp is a healthy material, meaning the environment of the homes built with it will contain fewer toxins than many other modern homes. Concerns about infestation are unfounded, as the binder used in Hempcrete protects against both insect and rodent infestation.

I wonder if a 16% growth each year is realistic, but it would be good to see more traditional building materials coming back into use, especially if this has a positive impact on carbon capture. As ever, the growing use of hemp-lime will come down to costs. If it is cost effective to use it in new developments – especially eco-conscious ones – we’ll see its use grow. It will be interesting to see what happens.

Meanwhile, if you need assistance with the structural elements of an upcoming project, please do get in touch.