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Hempcrete, the “Carbon Negative” Building Material

Hempcrete, the “Carbon Negative” Building Material

May 28, 2020

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. 

Hempcrete Buildings

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.

How long has Hempcrete been in use?

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. 

Resistant to Cracking

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.  

Four advantages of using Hempcrete in buildings.

    • Thermal Regulation
      • Thanks to its excellent ability to diffuse the accumulated heat, the Hempcrete naturally regulates the temperature of the building.  Keeping the heat in the house longer during cold winters and avoiding overheating of the habitat in hot summers.  It is a real thermal buffer, maintaining a constant indoor temperature and significantly reducing the impact of heat variations between day and night.
    • Humidity Regulation
      • Hempcrete acts as a water buffer, thanks to its high permeability to water vapor and offers a constant and healthy indoor climate for its occupants.  Its uses are.
      • Renovation and insulation of old buildings, old brick or damp wall.
      • Interior renovation to insulate walls on which wooden floors are resting, prevent any condensation issues in the transition areas between materials to guarantee the excellent conservation of the building.
      • Humidity regulation in commercial projects where humidity variations are high: archive rooms, museums and sports halls.
    • Acoustic Insulation
      • Whether Hempcrete is used for your walls or interior partitions, external and ambient noise will be significantly reduced.  In terms of sound insulation, the Hempcrete acts as a real sound trap and helps to dampen the majority of sound, protecting you from noise pollution.
    • A 100% Natural Solution
      • The Hempcrete meets the strictest requirements of sustainable development: manufactured according to a very low energy-consuming process, using 100% natural materials (limestone and hemp).  A very positive carbon footprint.

    In the United States, a permit is needed for the use of hemp in building.

     

    Hemp For Humans

     

     

     

    Sources: American Lime Technology, Wikipedia, National Hemp Association, American Hemp, and ISO Hemp

     

    Photo Credits to Hemp Solutions of Oregon, Ecological Architecture