MIT researchers developing process to make houses from recycled plastic

Massachusetts Institute of Technology researchers have made recycled plastic into floor trusses for housing, arguing the waste stream could provide an abundant and sustainable structural building material.

The US-based researchers 3D printed a functional, construction-grade element using a composite material they developed from recycled polyethylene terephthalate (rPET) plastic – mostly derived from discarded drinks bottles – mixed with glass fibres.

In the future, they say the system could be used in place of wood for house frames, making residential building cheaper while avoiding the overexploitation of forests.

"We've estimated that the world needs about 1 billion new homes by 2050," said engineer and inventor AJ Perez, who led the project. "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."

PET is "one of the most durable polymers"

To make the floor trusses, Perez and his collaborators 3D printed their polymer composite into a long rectangular element reinforced by an internal zigzag shape, similar to the structure of traditional wood and metal floor trusses.

Four of these trusses were configured into a plywood-topped floor frame and bend-tested by placing concrete blocks on top.

According to the researchers, the trusses only began to buckle and crack under more than 4,000 pounds (1,814 kilograms) of weight, exceeding US building standards.

Perez, who is a research scientist within the MIT Office of Innovation, also believes that the material is durable enough for structural use.

"PET is one of the most durable polymers," Perez told Dezeen. "The reason PET bottles are such a blight on the environment is that it takes approximately 450 years to break down naturally."

"We see this as the cornerstone of durability for the built-world uses we have demonstrated."

Unlike some plastics, PET is not brittle at room temperature, and although that changes in extreme cold, Perez argues this should not disqualify it from structural use.

"Our long-duration field testing in New England has demonstrated survivability and high-load endurance through three winters and three summers thus far," he said.

"The human element of this is critical to consider as well," Perez added. "The demand for housing globally is concentrated in the warm to moderate parts of the planet where such extreme deep freeze is not happening."

Researchers aim to make multiple components from "dirty plastic"

Together with mechanical engineering professor David Hardt, Perez is one of the founders of the MIT HAUS research group, which focuses wholly on producing homes using recycled plastics and large-scale additive manufacturing.

While 3D-printing using concrete or clay is more established within the architecture industry, Perez and Hardt believe recycled plastic has a lower environmental impact and is more versatile, allowing them to go beyond printing walls.

As well as the floor trusses, Perez has already used the recycled plastic composite to make a house foundation, and MIT HAUS also aims to print stair stringers, roof trusses, wall studs and joists.

The eventual aim is to use "dirty plastic" – uncleaned and unprocessed post-consumer waste like bottles and food containers – fed directly into a large 3D-printing system, which could be located in dispersed microfactories the size of shipping containers.

"We are starting to crack the code on the ability to process and print really dirty plastic," said Perez.

Because the resulting building components are light, they could then be transported on a pick-up truck or even a moped, according to Perez, and fitted together on site.

Material is recyclable and expected to be found safe "in time"

The rPET and glass composite is fully recyclable, said Perez, and any component made from it could be ground up and reshaped into another building or architectural component at the end of its life.

When it comes to the potential toxicity of the material in the case of a forest fire, Perez indicated he believes it is safe based on current scientific literature, but that MIT HAUS will investigate it thoroughly.

"Most 'mass timber' and other traditional 'wood composites' such as plywood or OSB, which is fantastic branding by the way, are really and truly just glue wood," said Perez. "These 'glue wood' products meet code, human safety standards, and are ubiquitous. We just don't call it what it is – a wood plastic composite."

"We anticipate that the same will prove true in time for the recycled plastic composite material we utilise," he continued. "In my opinion, the recent fires are shining a light on the ignition risk of conventional class-C wood framing."

Perez and his colleagues detailed their design and manufacturing process in a peer-reviewed paper presented as part of the Solid Freeform Fabrication 2025 symposium.

Another recent innovation using recycled plastic as a building material, although in this case a decorative one, is Pretty Plastic tiling. Developed by architects Overtreders W and Bureau SLA, the tiles are made from notoriously hard-to-recycle PVC.

Top image is by Zeynep Ergani via Shutterstock.

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