Construction companies have been experimenting with 3D printing for years, but next year, a major homebuilder will break ground in Austin, Texas, on what will be the largest such development to date.
The new community will consist of 100 homes built with first floors made from 3D-printed concrete and finished using traditional wood-frame construction techniques. Construction technology startup Icon will be handling the 3D-printing portion, and Lennar, a large homebuilding firm, will finish the homes off. Bjarke Ingles Group, known for its creative and whimsical buildings, is assisting with the design.
Icon had previously built four homes in Austin using its 3D-printing technology. “We’re sort of graduating from singles and dozens of homes to hundreds of homes,” CEO Jason Ballard told The Wall Street Journal.
Though the company hopes that 3D printing will ultimately be cheaper and faster than traditional construction methods, homes in the planned Austin development will take about as long to build and cost about as much as homes built using wood framing. Currently, Icon can 3D-print the first floor of a home in about a week, which is how long it takes homebuilders to frame and drywall using traditional methods, Lennar said.
Ultimately, the building industry hopes that new technologies will help alleviate worker shortages, which continue to plague the sector despite higher unemployment rates.
Technology Squeezing out homes
To build the first floor of a home, Icon sets up a gantry-style 3D printer, which effectively places a giant frame around the home’s footprint and supports the printing head as it roams about. Concrete is squeezed out of a nozzle and looks like soft-serve ice cream. The resulting walls have a layered appearance that resembles a squished stack of pancakes. Other companies forgo the gantry, instead using a robotic arm that they move around the building site. The end result looks pretty much the same.
Previous builds apparently relied on the material’s thermal mass to keep occupants comfortable. That works in regions that experience wide day-to-night temperature swings but relatively small differences between seasons—the thermal mass will buffer the daily highs and lows. But for places that experience greater temperature variations between seasons—or consistently warm or cool conditions—concrete-walled homes without additional insulation would become too hot or too cold for comfort. Icon’s newer homes have spray foam insulation injected in the air space between the exterior and interior concrete walls.
Many 3D-printing building companies claim their technologies can help alleviate housing shortages by slashing construction times and labor costs. Currently, that’s not the case, but Lennar hopes that as the technology matures, its speed will increase.
Technology Counting carbon
Another common claim is that 3D printing can lower the environmental impact of homebuilding. That claim seems to rely on waste reduction. Since 3D printing is additive rather than subtractive—printing only uses the material it needs, while carpenters must cut wood down to length—the claim will probably withstand scrutiny.
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Several companies are experimenting with 3D printing in homebuilding, and most have converged on concrete as their material of choice. Icon uses a proprietary mix it calls Lavacrete, which combines typical Portland cement with “advanced additives” intended to help it survive extreme weather.
But by using concrete, the carbon footprint of those homes could be significantly larger. Cement, the key binding agent of concrete, is responsible for 8 percent of the world’s carbon pollution, much of it coming from when limestone is heated, a process that alters the rock’s molecular structure and releases carbon dioxide. On the other hand, wood naturally sequesters carbon. One square meter of floor space supported by concrete has a carbon footprint nearly seven times larger than one supported by wood beams, according to one study. (The type of insulation best suited to this application—spray foam—often uses gases with high global warming potential, but newer formulations are seeking to address the issue.)
There are currently various attempts to decarbonize cement, and one 3D-printing company, Mighty Buildings, is working with a materials science startup, Fortera, to use cement made from carbon dioxide, which the companies claim reduces the carbon footprint by 60 percent.
Another alternative would be to dispense with traditional cement altogether. Materials scientist Sarbajit Banerjee and his collaborators from Texas A&M came up with a cement-like material made from silicates combined with nearby clay, alkaline water, and some cellulose. Once cured, the 3D-printable material withstood nearly 430 psi (about 3 MPa) of pressure. That’s far short of concrete—other, non-3D-printed formulations get closer—but it’s not bad for a first pass.
Correction, 3 pm: Icon’s newer homes have insulation inside the double-layer concrete walls. We’ve updated the article to reflect that.
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