Hemp is a fast growing crop that is finally making a come back. It is truly versatile in that it can be used as medicine, fuel, clothing, and so much more. It grows so fast that weeds cannot even take root. It needs no pesticides. It is truly a very environmentally friendly crop. As a building material, it is natural, strong, and can last many many many years. When mixed and set correctly, it is mold, fire, and pest resistant. It provides incredible insulation AND thermal mass in one, whereas most of the other green building techniques we've looked at are either one or the other. It has an R value of around 25 per foot of material, and has the thermal mass so that it can contain and slowly release heat/cooling into the interior of the building.
To build with hempcrete is a relatively simple process. The core fibers, or "shiv" is dried, and then mixed with water and a binder, generally lime. I have seen some recipes that also add cement. Most don't. It is not used as the sole material of the walls. There must be a post and beam frame of some kind. The hempcrete is then put in place using a techniques similar to that used in rammed earth. A shutter, or framework, is temporarily put in place. The hemp mix is then poured and compacted in. The shutters can be removed within hours. At that point, the hempcrete is solid enough to stand on it's own, but it will still need up to two days to completely dry. It can also be sprayed into place in the frame. It can be used in floors, walls, and ceilings. It cannot, however, be used in underground or earth bermed structures. It needs to breathe, so airflow on both sides of the wall is critical. Different suppliers of the binders will recommend the amount of water. Hemp will absorb part of the water, and the lime needs water to properly set. When in doubt, always refer to instructions and/or professionals to get the right mix.
For the plumbing and electrical, those should be put into place before the hempcrete is filled in. It just makes things easier and more efficient in the overall process. If you want to have a type of in-floor heating system, that can be applied within the hempcrete, as well. Once the walls have dried, a render is then placed on the outside, with a final coat of lime. The interior walls can either be left as is, or covered with a lime and/or clay finish. But, just as with other green building styles, whatever you use for the finishes, it must be a natural breathable material. I cannot stress enough, it must be able to breathe. Do not use any sealers or paints that cannot breathe.
Until recently, hemp providers were difficult to come by, at least here in the US. Thankfully, that is changing. Hempcrete is an amazing material. Once the foundation and framing has been done, a hempcrete structure can come together fairly quickly. If you want a home that is fast, environmentally friendly, and little upkeep, hempcrete may be the right choice for you.
As with all the other methods I've discussed, I am by no means an expert. I'm just here to provide enough information to give you a jumping off point for further research. Learn as much as you can, and attend workshops whenever possible. Following is a rather lengthy list of online resources for your perusing pleasure.
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