BioHome3D Printed with Bio-Based Materials

The University of Maine’s Advanced Structures and Composites Center has produced a prototype 3D printed house made entirely of bio-based materials. The 600-sq.-ft. structure is composed of wood fibers and what the Composites Center described as bio-resins, making the building fully recyclable. All the components of the house—roof, walls, and floors—were printed on what the university says is the largest polymer 3D printer in the world.

Printed in four modules of roughly 10,000 lb. each, BioHome3D was assembled on a foundation outside the Composites Center in about half a day, with virtually no production waste. Electrical service was up and running within two hours.

Concrete, a material with high embodied carbon and very low R-values, seems to be the most common material used to print houses. BioHome3D addresses both of those shortcomings with its wood-fiber mix. The house is actually made out of insulation—wood fiber and blown-in cellulose. The Composites Center says R-values can be customized for the needs of a particular site.

Printing BioHome3D capped decades of research at the university including tests of an extruded wood-based material all over the world. In equatorial regions, it out-performed pressure-treated wood. The process starts with wood residuals left over from sawmills, which once went to pulp and paper mills. The wood fiber is ground down to micro- and nano-sized particles and combined with a resin that can be derived from corn, wood, or other materials (the exact resin mix for this house was not disclosed). About 60% of the material is wood flour by weight and the rest is resin.

The printed material resists decay because of the resin that prevents water intrusion. When it’s time to recycle a building, it’s simply ground up with the residue sent through the printer another time.

One advantage of the printing process is that the thickness of walls and roof—and therefore the R-value of the building—can be adjusted to meet site conditions. In the demonstration house, walls are roughly 10 in. thick, and the roof a bit thicker than that. That might not be enough to meet current code requirements for Maine, which falls in climate zone 6, but making them thicker is not a problem.

“You can scale the cavity thickness to anything you want because the printer doesn’t care,” a spokesman said. “When you go buy lumber you can’t find 2x14s. They just don’t exist. But in our case, 2x14s aren’t a problem . . . and 2x16s aren’t a problem. We can scale the walls to whatever R- value you’re interested in. Our goal is R-value by design . . . we can scale the thickness of the wall to do what’s required.”

Wall sections are printed with an inner and outer layer. The two are connected with a truss-like reinforcement, and the cavity filled with cellulose insulation. The all bio-material assembly is a much better insulator than concrete, and it also sequesters carbon. If the process could include sustainably grown forests as the source for the wood, he said, “the trees become carbon sequestration and the house becomes a carbon storage unit, and that’s the way we see this particular process.”

Ultimately, the goal is to print a house this size in 48 hours., at which point he believes it would be cheaper to build than a conventionally framed building.

BioHome3D is equipped with a variety of sensors to measure thermal resistance, thermal bridging, structural integrity and other values key to understanding the process better. Some of the walls were left as printed, and others covered with drywall, to show visitors that different options are possible. But the raw bio-material has been a hit.

“People love the looks of it,” he said. “When they walk in they say wow, I want to live in this. I haven’t seen one person who comes in who doesn’t want to live here. It’s got a very warm feeling.

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