Eco-construction: the revenge of hemp
Outraged, humiliated and beaten by cotton and synthetic fibers, forgotten and almost eradicated from the French countryside, had agricultural hemp said its last word? No ! In the construction industry, it is now an “eco-material”, appreciated for its ecological, economical and aesthetic qualities.
Hemp and new energy standards
Like most of the new “eco-materials”, hemp is in fact distinguished by its age because it has been cultivated by man since the Neolithic period for the quality of its fiber. It was used for several millennia to make clothes, ropes, cosmetics and later, paper. The beginning of the twentieth century was almost fatal, with the massive arrival of cotton from the United States, then the development of synthetic fibers, which were faster and cheaper to produce.
France was then a major producer of industrial hemp, totaling in the 19th century 175 000 hectares of land devoted to the crop. Hemp then almost completely deserted the French countryside. Nowadays, and despite the revival of this plant, only 7,000 hectares of hemp are cultivated, mainly in Champagne-Ardenne, in the Paris region, in Brittany, in Haute-Garonne and in the Loire region.
We must speak of renewal, since hemp has entered a completely unexpected area: construction. At the beginning of the 1990s, experiments led to revealing the astonishing energetic qualities of hemp both in insulation and as a building material in its own right, with moreover an ecological interest far superior to concrete.
The 2000s ended up highlighting the alarming deterioration of the climate, and the need to change habits. In France, a series of energy legislative measures ("RT") recently confirmed this state of affairs, forcing new buildings to comply with increasingly draconian energy standards. Ultimately, the “RT2020” should tend towards the complete passivity of buildings, and even towards autonomous energy production.
Wool, brick and hemp concrete: always more ecological
For hemp, thanks to these new energy requirements, it's time for revenge. The characteristics of hemp fibers make it a very good natural thermal and acoustic insulator. Hemp wool is used in the form of bulk, rolls or semi-rigid panels. In these last two cases, the addition of about 20% polyester fibers is necessary to ensure the cohesion of the product. Hemp wool is suitable for wall insulation as well as for roofs and floors.
Hemp is also used as a building material. The “hemp brick” covers a sort of concrete block made up mainly of chènevotte, designating the hemp stem. Excellent thermal insulator, hemp brick is often used to line existing walls by internal thermal insulation (ITI), or by external thermal insulation (ITE). However, it is strong enough to be used in its own right with a wooden or steel frame.
More surprisingly, hemp is also used in an evolved form of hemp brick, as "shot hemp concrete". It is a mixture of hemp and lime, placed in a special machine that projects the product into a pneumatic hose. On leaving, the mixture receives a spray of water and is thus projected into a construction formwork, or onto an existing wall.
This recent method again provides good thermal insulation and excellent acoustic insulation, with a density much lower than concrete.