“It’s simple and beautiful. Sometimes simplicity is not easy to obtain”: in front of a textured-looking wall, made up of thin concrete rods stacked horizontally on top of each other, Rochdi Zardi, 60, tenant who will move in on July 1 with his family, has a broad smile.

“I’ve been looking for social housing on one level for a year,” explains this former teacher and former supermarket manager, who no longer works to be able to take care of his severely disabled wife.

The rent for his future house with three bedrooms and a garden, built in the Rema’Vert eco-district on a former railway site, amounts to 920 euros per month, instead of 700 for his current apartment upstairs.

“Here, it will be a little more expensive as rent, but when you compare what you have, it’s very correct. When you see the prices in the private sector! In addition, a house like that, new!”, s he exclaims.

In fact, the walls mounted by the back and forth of a printer head loaded with liquid concrete which solidifies during formation, allow creativity. In particular to imagine curved walls à la carte, a luxury for social housing.

Here, 3D printing was not used everywhere, only for 35 walls of the five interconnected houses (kitchens, bathrooms, toilets using conventional walls).

An entire 3D wall, produced by the startup XtreeE, based in Rungis in Val-de-Marne, is about twenty centimeters thick. It is composed of two walls of a few centimeters, linked together by stiffeners (kinds of concrete zigzag) which ensure the cohesion of the whole. The space in the center is empty, and can be used to accommodate insulation, either in rock wool or in biosourced materials such as hemp.

“This allows a dry site, in the workshop, no concrete poured under the weather, to build faster with fewer hazards and without carrying breeze blocks, because the walls are transported by truck and carried by crane”, underlines Romain Duballet , director of XtreeE Studio.

Above all, the technique would make it possible to use 50% less concrete than a traditional construction with a reinforced concrete wall poured between two vertical formwork elements called formwork, argue its promoters.

– “Freedom of forms” –

One to three walls were printed per day. “What 3D allows above all is to go faster, to reduce the difficulty of the construction”, says Florent Haas, director of the Champagne agency of the builder Demathieu Bard Construction who coordinated the site.

The method also reduces waste. “On average around 30% of materials are wasted on a classic construction site”, estimates Emmanuel Coste, the project architect, for whom its main advantage is “the freedom of forms”.

The initiative for the technique comes from the social landlord Plurial Novilia, based in Champagne-Ardenne and Ile-de-France, which fought to obtain certification of the 3D process by the Scientific and Technical Center for Building (CSTV).

This approval guarantees “insurability” to the five houses by providing them with the precious “ten-year guarantee” engaging the responsibility of the builders, including the architect, for ten years against poor workmanship, a French construction standard which is among the strictest in the world.

For 3D, “we have developed a high-performance concrete to withstand pressure, but with less cement to reduce greenhouse gas emissions”, explains Olivier Martinage, head of concrete 3D printing at the cement group Vicat. who participated in the adventure. His next challenge is to also use recycled aggregates in the printer, to further reduce the impact on the climate, as the cement manufacturing process emits a lot of carbon dioxide.

But for the architect Emmanuel Coste, the main challenge will certainly be to manage “to print walls with something other than concrete”.

“Concrete is the solution we have at hand for the moment, but it still emits a lot of greenhouse gases, it is clear that we will have to get out of it”.