Have you heard of a not so new building material called “Hempcrete”? It is a bio-composite made of the inner woody core of industrial hemp. Hemp hurds (or “Shiv”) have a high silica content which allows them to bind well with lime. Hemp, water and lime (powdered limestone) are mixed together in a slurry and form into the wall of a building.
Over time the chemical reactions between the water, lime and hemp will petrify the hemp and turn the lime back into stone, which results in a lightweight cementitious insulating material weighing a fraction of concrete. It is not a structural element, but is a good insulating infill between frame members though it does reduce cracking. Loads are carried by internal framing. Most common framing is wood stud, making it suitable for low-rise construction. However, buildings of Hempcrete ten stories high have been built in Europe.
It was discovered in a bridge abutment in France built in the 6th century. Given the bridge survived 14 centuries it is expected that Hempcrete buildings will have a long life. France has been using Hempcrete to construct non-weight bearing insulating infill walls, since the early 1990’s. Since it’s rediscovery it has seen growing use in Europe.
Hempcrete does not have the requisite strength for foundation construction, it is instead supported by the frame. It is also used to renovate old buildings made of stone or lime. Hempcrete is growing in popularity annually in France. It is a low density material and resistant to cracking under movement, thus making it suitable for use in earthquake-prone areas. Hempcrete walls must be used together with a frame of another material that supports the vertical load in building construction, as Hempcrete’s density is 15% that of traditional concrete.
In the United States, a permit is needed for the use of hemp in building.