Green Is Green: Building With Hemp

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Hemp worms eye view

A friend sent me a post about various building methods. On page one was a paragraph about cannabricks. I’d never heard of them before, but then I realized it is the same as Hempcrete®. I thought this may have been a new name for it, but when I googled ‘cannabricks’, I found information from almost 10 years ago!

Hemp, known as dagga, has been a traditional building material in South Africa for thousands of years, but like in the US, it has been outlawed. In 2005, hemp advocates were protesting to remove the ban on industrial hemp to solve the problem of unaffordable housing.

Despite the prohibition, hemp is still grown in rural areas, and instructions for growing, harvesting and building with it are readily available. My favorite line in that article is The seed can be gathered for more housing.

Sustainable, renewable and local

I am thrifty, frugal, and resourceful, so the idea of growing the crop needed to build a new house is really exciting! It doesn’t get more sustainable or local than that.

The instructions suggest a planted acre is necessary to build a small 5-room house. I looked out my window to my .87 acre and thought, ‘I could plant my entire lot and have enough hemp to build a 3-room house!’ Even though we build adobe bricks from the mud in our yards, there is something more alluring about growing the crop that makes the bricks. That must be the gardener in me talking…

Green is green

Hemp converts CO2 to oxygen, it can be grown close to where it will be used, it takes very little fossil fuel energy to convert into a usable material, there is little waste in production, and it has insulating and thermal properties. These factors make it carbon neutral. You can’t get more eco-friendly than that!

Hemp can be grown with little water and no pesticides. How perfect is that to conserve resources? A crop can be harvested in four months. In warm regions, that means more than one harvest a year. With a cold hardy variety, it would be possible for multiple harvests in cooler climates, too. Cannabricks are completely recyclable and biodegradable, being made only of hemp, water and lime.

As a building material

Hemp is mildew, mold and fire resistant. It is watertight and durable, but it does not have good acoustic qualities, the way adobe and strawbale absorb sound.

It can be made into bricks, but it can also be made as a mash and pounded into a form layer by layer, the way rammed earth walls are made. This is a less labor-intensive method, but it takes longer as the layers dry between applications. Hemp does not have load-bearing properties, so a frame must be erected, and the bricks or forms placed within it as walls.

My new favorite building material?

Every time I think I have found my favorite building material (cob was my latest crush), I find something else. I was already in love with hemp’s organic and renewable qualities, but now that I can grow my own, I think I’m committed. I should have been a contractor so I could try all these ideas out…

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Nan Fischer

Nan Fischer has been living and building green for over 35 years. Nan’s emphasis on the BuildDirect blog is about how to make your dollar stretch further, while also moving toward a more sustainable lifestyle, as well as upcoming and existing technology to help us live in an ecologically-friendly way. Nan also authors posts on the website of her seed business, sweetly seeds.