"For sale: a new ranch-style, 130 square meter house located in Long Island, New York. Three bedrooms, living room, open kitchen, two bathrooms, garage. Starting price: $300,000. Special feature: it will be the first 3D-printed house sold in the United States." Since the ad appeared in February, Kirk Andersen's phone has been ringing off the hook: SQ4D, the start-up he runs, has developed the 3D-printing technology that will get this house off the ground in a few weeks... if the construction goes as planned.

3D-printer XXL version

SQ4D is not new to this. At the end of 2019, the 12-person company printed its first building that serves as a model house. "We printed the entire wall in 48 hours," says Kirk Andersen. "We used that to test our technology, and also to get all the approvals so we could sell the next house. This all took over a year because of the COVID-19 crisis."

SQ4D's technology resembles an XXL version of the most common 3D-printers. On a large gantry circulates a print head whose movements, controlled by computer, follow the plan of the house. With each pass, a nozzle deposits a layer of concrete of about two centimeters. These superimposed layers end up forming the exterior walls of the house, as well as the partitions that will separate the rooms. All that remains to be done is to install the roof, doors, windows, pipes and electrical conduits, and you have a house ready to live in within a few days.

There is no need to transport large prefabricated elements to the construction site.

For the past 10 years, researchers and entrepreneurs have been exploring this new approach. Demonstrators, pilot projects and other "proofs of concept" have multiplied in the United States, Europe and China, whether for housing or infrastructure. But the first commercial applications are just now beginning to appear.

"In the world of construction, innovation is always slower than in other fields," says Edelio Bermejo, head of R&D at LafargeHolcim. "Today, it is clear that 3D-printing is the technology that will enable a significant increase in productivity in this sector. We are just at the very beginning, and it is going to go very fast. Analysts estimate that this market will grow from $3 million in 2019 to $1.6 billion in 2024."

60% less material

The main advantage is the speed of execution. "There is less handling, fewer operations and less risk of accidents on the job site," says Andersen. Once the walls are erected — which takes between 48 hours and a week depending on the builder — the gantry that serves as a printer can be dismantled and reassembled on another plot. In the case of large structures, such as the wind turbine bases LafargeHolcim has been working on, the ability to print directly on site also reduces logistics costs: There is no need to transport large prefabricated elements to the construction site. 3D-printing also means that less raw material can be used, by adapting the interior of the printed structure to guarantee the same strength as a solid wall, for example.

A 3D printer at a Moscow laboratory, in February 2021. — Photo: Gavriil Grigorov/TASS/ZUMA

"In a world where sustainability is becoming critical, printing allows us to put exactly the right amount of material in the right place," says Hélène Lombois-Burger, head of digital manufacturing at LafargeHolcim's Innovation Center. "In the case of bridges, most projects manage to provide the same functionality with 60% less material."

In a world where sustainability is becoming critical, printing allows us to put exactly the right amount of material in the right place.

As in the United States, printed houses are coming to France: five semi-detached homes will soon be built by the social housing landlord Plurial Novilia in an eco-district in Reims. But the 3D-printing will be partial, and will not be done on-site. Each home will consist of a prefabricated rectangular module with curved exterior walls, all different, printed by XtreeE in its workshop in Rungis (Val-de-Marne). This approach, known as "off-site," is slower and less spectacular than printing a whole house, but it offers more flexibility. "3D-printing is not necessarily relevant for building all the elements of a house," says Jean-Daniel Kuhn, CEO of XtreeE. "If all the walls and partitions are printed, you make the building rigid, with partitions that are not removable, and it consumes more concrete."

Projects of all sizes

Concrete 3D-printing isn't limited to making houses. Here's a roundup of other current uses:

Shelters: Before single-family homes, several experiments have been conducted on the construction of small structures (one or two rooms), intended for emergency shelter or for people in need. In 2019, the NGO New Story partnered with the American start-up ICON to build such shelters in Tabasco, Mexico. Last year, ICON also built shelters for the homeless in Austin, Texas.

Schools: 3D-printing is being used to try to address the lack of school buildings in Africa. Last December, 14Trees, a joint venture between LafargeHolcim and the UK's CDC Group, built the first 3D-printed school in Malawi. Others are already planned in Kenya and Zimbabwe.

Bridges: As it uses less material for equivalent strength, 3D-printing has already been used for bridges in the Netherlands and China. In France, XtreeE will build a 40-meter-long footbridge over the Saint-Denis Canal in anticipation of the 2024 Olympic Games.

Wind turbine bases: GE Renewable Energy, LafargeHolcim and Danish start-up Cobod are working on printed towers that will serve as bases for high-rise wind turbines. Two 10-meter high prototypes have already been built.