Hemp Concrete Walls: The Bet of Wall up in Seine-ET-Marne

Ile-de-France is setting up a hybrid prefabrication site to explore the possibility of manufacturing pre-fabricated walls incorporating hemp concrete. The project is drawing the attention of investors. More than 600,000 euros have been allocated under a scheme named the PIA III Wood plan to develop technology that could replace the usual insulation materials made of mineral wool.

In Paris, we were expecting the development of prefabrication sites for wood construction, as there are at Méha in Valadon, Vaninetti in Rosny-sur-Seine. This handful of sites in Ile-de-France prefabricate timber frame construction elements, which are load-bearing walls and incorporate panel insulation guaranteeing high insulation performance for a reduced wall thickness.

According to guidelines that have been revised, the usual insulation is made of mineral wool. But there are alternatives based on bio-based insulation, like hemp concrete. However, neither the wooden components of the frames nor the bio-based hemp insulation come from the Paris region. And for the moment, almost all the prefabricated wooden frame elements are manufactured outside Ile-de-France.

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A Hybrid Hemp Concrete Solution

Instead of this commonplace but still rare prefabrication technique, Ile-de-France is setting up a hybrid prefabrication site. Walls made from a wooden frame are, in principle, not load-bearing, as the integrated insulation has the slightly lower performance of a hydraulic mixture and prefabrication requires setting times.

On the other hand, it is a prefabrication technique which makes it possible to introduce in a short circuit and by a process of prefabrication in the workshop and assembly the hemp that grows at the gates of Paris.

The hybrid character of Wall Up continues with the possibility of applying bio-sourced insulation to the facade carrying plaster, External Thermal Insulation Composite Systems (ETICS), or wooden cladding. Conversely, the panels can come to be fixed on a concrete post-beam structure. This is precisely the case for the activity building which has just been inaugurated, and which is based on concrete pillars chosen to support overhead cranes.

Concrete or Bio-Based Construction?

The possible destination of non-load-bearing walls is therefore hybrid and thus very flexible. Hybrid is also the combination of a wooden box and a fluid mixture of chènevotte and a lime-based product from Lhoist, which contains a part of hydraulic binders.

It is therefore permissible to speak of hemp concrete walls, just as we could speak of bio-based walls due to the concentration of bio-based materials, wood for the caissons, and hemp for the concrete. And the easiest is to call this hybrid Wall Up. A quarter of a century after the Toubon law, French brands are massively adopting English.

Hybrid is also the story of the product. Originally, the handling of lime, the hemp-lime mixture, is typically a masonry activity. In Ille-et-Vilaine, the LB éco habitat company is one of them. From 2015, Christophe Lubert developed the option of prefabrication there, particularly exemplified in 2018 for the offices of the Triballat company.

Speed ​​up the Setting of the Hemp Concrete Mixture

The innovation does not lie in the boxes, but rather in the R & D of Lhoist which puts on the market applications allowing to considerably accelerate the setting of the mixture incorporating the hemp seed.

The setting lasts 8 hours flat, then lifting. However, two weeks remain necessary for total drying, which means that half of the Aulnoy site near Coulommiers is a storage place for panels which are part of their setting flat. In Bédée, LB Ecohabitat does not have suitable covered premises. 

However, two weeks remain necessary for the setting, which means that the Aulnoy site near Coulommiers is largely a storage place for panels which are part of their setting flat. In Noyal, LB Ecohabitat does not have suitable covered premises.

The Footprint of Timber Construction

The Triballat site did not escape Lhoist and was spotted by Karibati who presented it a few years ago as part of a demonstration on bio-based construction. At this time, a hemp dynamic developed in Ile-de-France, with the creation of two hemp plantations.

Among the biobased construction products, hemp holds the rope in any case against wood and even with respect to straw. Except that the Ile-de-France region is still largely supplied with timber.

The architect Philippe Lamarque understands the interest of developing this type of prefabricated hemp-based wall. The Ile-de-France region too. The carpenters Méha, Aux Charpentiers de France (Delaunay group) and Paris Charpente are the three Ile-de-France carpenters who undertake to produce and supply the caissons, even if other suppliers could join them.

The boxes are not standardized in terms of format, contour and depth but comply with the specifications of the Wall Up design office. They arrive at Aulnoy, then are filled with the Hemp Concrete mixture. It is possible to increase the thickness beyond the boxes, and to apply any type of finish (cladding, plaster, carpentry, etc.) directly at the factory.

Hemp Concrete Manufacturing Method Based on Boxes

The wooden framework is used for handling these walls in the workshop, during transport and during assembly. Manufacturing can already integrate switches and therefore networks into reservation.

The prefabrication method based on caissons, involving several supplier carpenters and leading to assemblies on dry sites, all this brings Wall Up strongly closer to the world of timber construction.

As well as the appointment, at the head of the new factory, of Arthur Cordelier, the young journeyman carpenter who coordinated from the summer of 2019 the experimental and educational manufacture of the project “study and reproductions of the frames of Notre Dame de Paris” composed of a model exhibition and an almost real ladder span.

The Price of Bio-Based: Still Uncertainties

For now, it is very difficult to quantify the economic performance of Wall Up. The first panel made in the new factory served as a commemorative plaque. The whole is complex: boxes to be manufactured in addition to the overflowing activity on a market of strong tensions of deadlines and prices.

The process in Aulnoy which will require adjustments as is natural in a new niche of activity. The transport of the walls by road, certainly not far but all the same in a blocked region, the assembly rates which must be well supervised.

Finally, the installed Wall Up wall is not finished, but it can be. We therefore do not know if the solution is competitive, but on the other hand, the order book is filling up quickly. It is a question of delivering walls for teacher accommodation in St Ouen, and also others for the Woodi eco-district near Melun.

The good thing is that the investment has remained modest and has benefited from the aid of the State and the Region. More than 600,000 euros have been allocated under the PIA III Wood plan, another point that brings Wall Up closer to the wood industry.

Evidence points to a good carbon footprint, but proof of a carbon-neutral construction remains to be provided. Today it is the blue ribbon of construction, and despite the grouped FDES, it is still very difficult to properly carry out the carbon footprint of a given site. Maybe Wall Up will be a driving force in this area.

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(Featured image by  Chmee2 via Wikimedia Commons)

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