Start of a long journey – on our way to a hemp workshop back in September 2014
So we’re going to build with hemp and lime and let’s just get one thing out of the way: no, it’s not the smokeable kind. People joke that if our house caught fire, the whole village would be high for a week. We wish (could be amusing)… but no.
This is the hemp that was used for ages for rope and also in ancient buildings like the Ellora Caves in India and a 6th Century bridge in France. And it’s now getting rediscovered again as a building material, mixed together mostly with lime and often then known as hempcrete. It’s done quite a bit in France, but rarely in our neck of the woods and never in our village. Until now.
Why have we chosen to use it? Well, when we started looking at how to build as eco as possible, it seemed like a lot of it was about making the house really well-insulated and air tight with all sorts of complicated fossil-fuel based materials and layers, which are often impregnated with chemicals to make them fire retardant and repel insects.
Hempcrete really appealed to us for lots of reasons but basically these five:
1. It’s natural – hemp can be grown locally and quickly, and doesn’t need pesticides. Together with lime it creates a building material that is free from toxins, naturally impervious to mould and pests and virtually fireproof. And completely recyclable at the end of its life.
2. It’s breathable – hempcrete has this amazing ability to absorb humidity in the air and give it off again slowly: it breathes. By contrast, a lot of well-insulated and passive homes are so tightly wrapped up in synthetic membranes that they can’t ‘sweat’ and you have to have mechanical ventilation systems to get the humidity out and keep the air ‘fresh’.
3. It’s warm – Hempcrete is pretty unique in combining both good insulation and thermal mass properties. Which means it stores heat and releases it slowly over a long time, helping to keep you warm in winter and cool in summer. Unlike straw bale walls which have really good insulation values but not much thermal mass and cob walls which have really good thermal mass but are poor insulators.
4. It’s better than zero-carbon – energy used in the construction and operation of homes and buildings accounts for around half of the UK’s total carbon dioxide emissions, according to the UK Green Building Council. A hempcrete wall stores an estimated 160kg of CO2 per m3, even after accounting for all the CO2 emitted producing the hemp and lime, transportation and construction etc, according to UK Hempcrete.
5. It’s flexible – we live in a seismic zone, one of the highest risk areas in France, and hempcrete appears to be a rather good material for dealing with seismic issues as it is slightly flexible and has ‘self-healing’ properties. This gets a bit technical and we hope we never have to test it.
“I look at the range of materials out there, I cannot find one to match hemp. I can’t find one that has such low embodied energy, locks carbon in, has such a low environmental impact… it’s an incredibly expedient building method.” Kevin McCloud
If you’re new to hempcrete and want more info, the UK Hempcrete site is a good place to start.
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