This is my second post about hempcrete in just a few days. Obviously I’m pretty excited about it. The last post listed quite a few advantages of hempcrete. This post with even more exciting advantages is based on an article in the most recent issue of The Owner Builder magazine called Growing Your Own House, by Hilary Fuerst. Hilary attended the first ever hempcrete workshop in Australia that sold out with over 50 attendants. (That’s very high for a natural building workshop.) Part of the reason for the strong interest is because growing hemp is now legal in New South Wales, Australia. There’s also a new book out (talk about perfect timing!) by Steve Allin – Building with Hemp that sounds really good.
Hempcrete is simply a mixture of industrial hemp, hydrated lime, sand and water. One key advantage of hempcrete is it is repellent to white ants and fire ants, which are a major problem in Australia. They’ll attack wood, straw bales and earthen structures such as cob and adobe. Hemp walls ‘breathe’ or allow moisture to pass through, discouraging the growth of mold. It’s carbon negative because it sequesters carbon when used as a building material. Hemp produces large quantities of fiber faster than forests without fertilizer or pesticides in most any soil, and is rapidly renewable. One 3-4 month crop on one hectare can produce enough hemp to build a 135 square meter (1,450 sq. ft.) house and small shed! It meets building codes, is fire-resistant, non-toxic, has good insulation properties and is simple to work with. The advantages go on and on. There’s even a centuries old hempcrete building in Japan that’s still standing.
There are three drawbacks to hempcrete in my opinion: 1. it’s not loadbearing — a frame is required to carry the loads, 2. forms are needed, which must be raised as you build, 3. it’s illegal to grow hemp in many places, so you’d typically have to ship materials from far away, thereby adding to the cost and environmental footprint.
However, I think there’s a simple solution to each of these drawbacks: 1. fill earthbags with hempcrete or similar mixture — wide earthbag walls should provide sufficient thickness to carry single story loads on small, simple structures, 2. earthbags would eliminate the need for forms and form work, 3. use vetiver grass instead of hemp, which also repels insects such as termites and is rot resistant. I haven’t worked with hempcrete yet, so my opinion is largely based on conjecture (with a lot of related building experience thrown in). More testing is needed. Anyway, I see a bright future for all these sustainable building systems, including earthbag, hempcrete and vetiver.
Want to learn more? Here’s another good hempcrete video that claims it is stronger than concrete and one sixth the weight. Madame France Pierre, a hempcrete builder in France, constructs about 300 homes a year using this material. She says it petrifies and turns to stone. She has thousands of orders, but is limited by the availability of hemp.
More good videos: