Hempcrete: Have you ‘Hurd’ about this local, low-carbon insulation?
Contrary to what you might assume by the name, Hempcrete is not a structural replacement for concrete. It is however an almost magical material with incredible fire resistant, temperature and moisture regulating, carbon sequestering, and acoustical qualities. More technically referred to as “bonded cellulose insulation”, hempcrete not only offsets carbon emissions but also facilitates healthy indoor air quality.
The process of creating hempcrete begins with the core of the hemp plant being stripped from fiber, and then undergoing decortication to become hemp hurds. Hemp hurds are then combined with lime and water to create the final mixture of hempcrete. Lime makes the hempcrete pest resistant and also anti-fungal because it has a pH of 8.3.
The hemp hurd, lime, water mixture is tamped down between framing and formwork. The cure time in Colorado is around four weeks and only requires a finish as a final step. Interior finishes include lime plaster, hempwood, or milk paint and exterior finishes can range from wood paneling to brick or stucco. Most importantly, hempcrete should not be combined with a vapor barrier because it is a breathable (vapor open) material and naturally regulates humidity. Hemp hurds are very porous microscopically, which allows them to hold large amounts of moisture. Moisture in the wall is usually a bad thing in buildings, but the hempcrete can hold the moisture without growing mold, due to its antimicrobial properties from the lime (low PH). This allows the walls to hold and release moisture regardless of which way the vapor gradient is going.
Hempcrete has an R-value of 1.3 - 2.4 at one inch (depending on who installed it and the exact composition) but the R-value grows exponentially with thickness. This high insulative value is due to the porous nature of the material, which holds a lot of air. It also has incredible fire resistant properties and scored a 0/100 on the british flammability index.
Hempcrete has a negative embodied carbon of -2.73 kg of CO2 emitted per kg of hempcrete. That means that 7 million tons of CO2 could be sequestered per year in the U.S if hempcrete replaced traditional insulation methods. Additionally, hemp can be grown and harvested within mere months and the installation of hempcrete requires no power tools.
CGBG recently hosted a brown bag talk and Instagram interview with Eamonn McNaughton and Roland Gyallay-Pap of Rocky Mountain Hemp Build. Check out both videos below!