Hemp concrete, an anti-CO2 material

FIGARO DEMAIN – Concrete and hemp wool regulate the temperature while reducing the carbon footprint of buildings.

Sober and functional, the building designed by the North by Northwest architectural firm fits naturally into the Gallieni district in Boulogne-Billancourt (Hauts-de-Seine). In all discretion, it marks with a white stone the history of eco-construction in hemp.

25 meters high over eight floors, the facade designed in hemp concrete is the highest in France. Invisible to the naked eye, the Tradical solution from the company BCB is a mixture of vegetable fibers and lime sprayed on wooden panels. Despite its name, hemp concrete is not load-bearing – reinforced concrete remains essential – but it constitutes a natural air conditioner capable of regulating variations in temperature and humidity to obtain interior freshness in summer, and save energy. energy in winter.

Comfort is not the only motivation of the owner, the real estate company 3F, specialist in social housing. With the Boulogne-Billancourt building, the lessor anticipates the application of the RE2020 environmental standard. From January 2022, manufacturers will have to change their practices to reduce greenhouse gas emissions in order to fight against global warming. The variety of hemp used in the building, which has no psychotropic properties, is frugal in water as in pesticides. This virtuous plant, easy to grow in France, reduces the carbon footprint of construction, which consumes too much sand, glass wool and rock… The building industry is indeed one of the largest sectors emitting greenhouse gases. in France, with a quarter of national discharges.

Within the reach of any amateur

At the end of the 1980s, a first half-timbered house was renovated in Nogent-sur-Seine, followed in 2006 by the rehabilitation of the tourist office in Troyes. Lightweight and insulating, the hemp concrete fills and insulates the timber frames without weakening the old structures.

Proof that practices are still evolving, the promoter Legendre and the company Wall’Up are collaborating on future hemp concrete walls adapted to the Saint-Denis Athletes’ Village in anticipation of the 2024 Olympics. A daring handful is behind the scenes. from Wall’Up: Franck Barbier, president of Planète Chanvre, which brings together growers and carpenters from Île-de-France, and Philippe Lamarque, architect specializing in biomaterials. According to him, “The Paris region needs 70,000 new homes per year. We will be able to equip 1,500 ”. What to see the future with optimism. One of its competitors, Olivier Joreau, deputy general manager of the Cavac group, believes that “the plant insulation market, which includes hemp, wood, cellulose wadding and straw, represents 10% of the turnover of the insulation market. Double-digit annual growth is supported by citizens. ”

In fact, if handling concrete requires experience, insulating his house with hemp wool is within the reach of any hobbyist. DIY stores (Point.P, Leroy Merlin, etc.) offer this material that looks like beige felt that is easy to cut.

Today, around fifteen chanvrières and SMEs offer turnkey solutions. This is the case of Vieille Matériaux, in the Doubs, whose Biosys blocks, for example, produced with the cement manufacturer Vicat, incorporate both hemp and quick cement. They fit on top of each other to make facade walls.

What if a fire breaks out in a “green” house? In the collective imagination, only stone protects against fire. To reassure the undecided, manufacturers last year successfully submitted their products to official Lepir 2 fire resistance tests. Verdict: architects can use the bio-based material to build high schools and colleges that can accommodate up to ‘to 700 students. The beginning of pedagogy by example.


Le Figaro

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