The design they came up with is similar in shape to the traditional wooden trusses that support flooring, with beams that connect in a pattern resembling a ladder with diagonal rungs. To test it, they obtained pellets made of recycled PET polymers and glass fibers from an aerospace materials company and fed them into a room-size 3D printer as “ink.” When they printed four long trusses with this material and configured them into a conventional plywood-topped floor frame, the result had a load-bearing capacity of over 4,000 pounds, far exceeding key building standards set by the US Department of Housing and Urban Development.

The plastic-printed trusses weigh about 13 pounds each, light enough to transport without a flatbed truck. An industrial printer can crank one out in under 13 minutes. Crucially, the researchers are developing the process to work with “dirty” plastic that hasn’t been cleaned or preprocessed. In addition to floor trusses, they are working on printing other elements and combining them into a full frame for a modest-size house.

“We’ve estimated that the world needs about 1 billion new homes by 2050. If we try to make that many homes using wood, we would need to clear-cut the equivalent of the Amazon rainforest three times over,” says Perez. “The key here is: We recycle dirty plastic into building products for homes that are lighter, more durable, and sustainable.”

The researchers envision that one day, trash like used bottles and food containers could be sent directly into a shredder, turned into pellets, and fed into a large-scale additive manufacturing machine to become structural composite construction components. At the construction site, the elements could be quickly fitted into a lightweight yet sturdy home frame.

“The idea is to bring shipping containers close to where you know you’ll have a lot of plastic, like next to a football stadium,” Perez says. “Then you could use off-the-shelf shredding technology and feed that dirty shredded plastic into a large-scale additive manufacturing system, which could exist in micro-factories, just like bottling centers, around the world. You could print the parts for entire buildings that would be light enough to transport on a moped or pickup truck to where homes are most needed.”