Donnachadh McCarthy: The Home Ecologist

Hemp is the latest alternative to concrete. And like vegetables or fruit, it's locally grown

I have managed to avoid the home extension craze, involving as it does significant resource consumption and CO2 emissions. Globally, the concrete industry emits about 7 per cent of total CO2 emissions, due to the energy required to turn crushed limestone and clay into concrete.

The concrete blocks used in a typical home result in the emission of 40 tonnes of CO2, equivalent to seven years' worth of emissions from the house.

But if that extension is unavoidable, what can you do? This was the problem Adnams Brewery faced with their new eco-friendly distribution centre. Then the management hit on a solution. They teamed up with Lime Technology, who supplied Hemcrete blocks made from lime and hemp. Adnams even provided development funding to enable mass production of the 90,000 blocks.

The results were striking. Due to the insulation properties of the Hemcrete blocks, the new distribution centre requires no cooling systems to keep their precious stock of Adnams beers in top condition.

Hemcrete's manufacturers claim that because the hemp is grown in East Anglia using no fertilisers, they lock up CO2 from the atmosphere – so they're actually carbon-negative!

Adnams' decision to use Hemcrete blocks resulted in a net negative 150 tonnes of CO2. And of course, the fact that the new building requires no heating or cooling systems results in massive annual CO2 savings.

Hemcrete is now rolling out these blocks to the wider building industry. Previously, Hemcrete was only available by spraying it into wall-shaped moulds on site, generally in timber-framed buildings. They found that builders were often reluctant to try new systems, but were more open to using traditional-shaped hemp blocks. The blocks come in both structural and non-structural strength. The structural blocks have a strength of three newtons, which is the same as traditional concrete blocks and can be used in buildings up to three storeys high.

As a new product, Hemcrete has not achieved mass-market efficiencies yet, so it is still up to three times the price of concrete. By specifying them now, however, enlightened home owners and business people can provide a lead and help create a mass market for them, so that the good people at Hemcrete can bring the prices down soon.

I really love the idea of the Sixties baby-boomers proudly showing off their hemp collections – only this time pointing to their walls, rather than their gardens.

The author is an eco-auditor and is author of 'Easy Eco-auditing' www.3acorns.co.uk