Since Spain opened the first 3-D–printed pedestrian bridge in 2016, the push for printed architecture seems to be accelerating. Shanghai inaugurated the world’s longest printed concrete bridge in January, and the first-ever printed steel span is set to cross a canal in Amsterdam this year. Beyond bridges, the first 3-D–printed homes available to rent—five bulbous buildings in the Dutch city of Eindhoven—should hit the market by this summer.

Some of the artsy, even zany, designs seem like architectural fantasy. But some experts believe these novel prototypes could herald a major shift in the construction sector. “The building industry is very stubborn” when it comes to change, says Capt. Matthew Friedell, who leads the U.S. Marine Corps’ 3-D printing operations. But “once we prove 3-D printing’s advantages for construction at scale, its adoption will increase rapidly.”

In usual bridge construction, skilled workers mix concrete and pour it into plywood molds called forms. Large-scale 3-D printers, by contrast, pump out quick-setting concrete slurry from a nozzle on a crane or gantry arm that moves on rails, guided by a computer, to create entire structures layer by layer. Instead of making new forms for every piece, builders can reuse one printer to create a variety of projects. Without requiring forms—or skilled workers to construct them—a printer can get to work faster, with fewer materials and less labor.

In 2018, Marines used a concrete 3-D printer to construct a 500-square-foot barracks in Champaign, Illinois. Credit: Marine Corps Systems Command

Designing and building things like bridges fast and on the go is of obvious interest to the military, which often debuts new technology that eventually spreads into the commercial mainstream. It was the Marines who created the first 3-D– bridge in the U.S., a flat 32-foot span at California’s Camp Pendleton, late last year. They made it in a fifth of the time of traditional methods, Friedell says.

Typically soldiers transport cantilever-style mobile bridges, about $750,000 apiece, that they can later assemble to span water or rough terrain. A 3-D printer would cost about the same as one of those units, and the military would still have to carry its components to assemble on-site. But once it arrived, one printer could produce multiple bridges, buildings, walls and water storage tanks—anything the troops might need while deployed. For example, the Marines have also printed a concrete barracks large enough to accommodate eight soldiers, which they could use instead of shipping-container housing units.

In addition to providing greater flexibility, this option would cut costs and labor. The ingredients for concrete are cheap, and soldiers could source these raw materials locally, Friedell says. After that, their 3-D printer could run with minimal human input. “The ultimate goal,” Friedell says, “is to have one person stand there and hit ‘print’.” In fact, one report by the Associated General Contractors of America says some companies are looking at 3-D printing to help ease labor shortages.

Testing a 3-D printer that architects are using to build five concrete houses in Eindhoven, The Netherlands. Credit: Technical University of Eindhoven

Some believe these lower costs could be a game changer for affordable housing. Austin-based construction technology startup Icon recently unveiled a 3-D printer that the company claims can make a 2,000-square-foot family home in three days for about half the cost of traditional building methods. Icon says it plans to build affordable housing communities at sites in Austin and Latin America. “The idea that we can bring this cheap machine to make houses is pretty exciting, especially for humanitarian relief missions,” Friedell says. “And I see a direct correlation for the housing market.”

Although the home construction industry does not have the same needs that a military or relief mission does—assembling bridges or barracks quickly in remote places—it could still benefit from a building method that saves time, labor and building material. On top of that, printing can enable complex designs that are much harder to make with traditional methods. For example, according to Friedell, the sinuous walls of the Marines’ printed barracks are 2.5 times stronger than typical straight ones, but building those curvy walls the usual way (from individual concrete blocks) would have been much more difficult and time-consuming than printing them, he says.

Such complex designs can allow architects to use fewer materials. Take the first printed bridge in Spain, which resembles tangled vines: That pattern offers the highest strength possible using the least amount of cement. “By putting material exactly where you want it, you reduce consumption and wastage,” says Leroy Gardner, professor of structural engineering at Imperial College London. A study by researchers at Brunel University suggests 3-D printing could create up to 30 percent less material waste than typical construction techniques, as well as using less energy and generating fewer carbon dioxide emissions.

“Clearly this is an interesting technology with enormous potential,” says Timothy Gutowski, who leads the Environmentally Benign Manufacturing research group at Massachusetts Institute of Technology. But, he says, there is a need for more systematic studies to compare the environmental impacts of 3-D printing technology and conventional techniques over the entire life cycle of a structure, from its raw materials to the end of its life.

Most 3-D printers today, for instance, build with concrete—a material blamed for 7 percent of Earth’s carbon dioxide emissions, per the International Energy Agency. To combat this, some developers are working on more sustainable alternatives: In 2016 a Dutch architecture firm printed a tiny 86-square-foot cabin from a sustainable bioplastic, and in 2017 the University of Hong Kong demonstrated 3-D–printed terra-cotta bricks.

Gutowski also warns that the supposed reduction in cost and material use could fall prey to the rebound effect, a term used in economics: If something runs on less energy, for example, people will run it more, quashing energy savings. 3-D–printed homes might cut material use in theory—but that could encourage builders to go bigger. The benefits get diluted, Gutowski says, when “affluent people start putting on additions to their homes or making vacation homes.”

Despite the obstacles, architectural projects that rely on 3-D printing have continued to increase in number over the past five years. The explosion of interest is a sign of “an ongoing digital transition in the construction industry,” says Theo Salet, a concrete technology professor at the Eindhoven University of Technology, who is directing the Dutch project to print homes for rent.

The technology is still young, though, and requires more development to gain wider use. Printing a giant bridge or skyscraper will not truly be as easy as hitting a button in the foreseeable future, says Skylar Tibbits, a computational architect at MIT. Printers that work at this scale are still slow and expensive. And for now they only produce one kind of material at a time, so builders still have to manually integrate doors, windows, wiring and plumbing. In fact, aside from the Marines’ projects, which aimed for speedy on-site construction, most of the existing bridges and homes have been printed in parts that humans later assembled.

For now, Tibbits says, the construction industry will likely use 3-D printing to mass-produce modular components that still require human labor to put together. Printers might also be used to build structures with unique designs or to decorate them with intricate architectural details. “Printing,” Tibbits says, “is one of many tools you can utilize in harmony to create buildings and products.”