Hempcrete is a biocomposite made of the inner woody core of the hemp plant mixed. This property is unique to hemp among all natural fibers. The result is a lightweight cementitious insulating material weighing about a seventh or an eighth of the weight of concrete. Fully cured hempcrete blocks float in a bucket of water. It is not used as a structural element, only as insulating infill between the frame members though it does tend to reduce racking. Hempcrete is carbon-negative. Cement production and use generates too much CO2, the most of any man-made material.
Lime production is a lower temperature process that produces much less CO2 which it reabsorbs during curing as it mineralizes back to calcium carbonate. The hemp plant absorbs carbon as it grows. The lime absorbs more CO2. The result is a material that consumes more carbon than it produces. Hempcrete does not support termites Hempcrete is recyclable. When the house is demolished the material can be ground up and spread on farmer's fields. Concrete cannot do that. Landfill costs are a significant part of demolition costs. Eventually, landfills will become closed to construction debris.
One hemp house = 10 acres of trees. One hemp house can sequester the same amount of carbon as ten acres of trees. It takes 14 weeks to grow enough industrial hemp on 2.5 acres to build a 1,250-sq-foot house. The average Hempcrete building is expected to last 700 years. 2,500 Lbs. of industrial hemp are needed to produce the same amount of THC found in one marijuana cigarette.