The first 3D-printed, two-story concrete home in the U.S.

Sasa Zivkovic stood on a 4-meter platform looking down onto the ribbons of concrete being extruded in continuous movement, one after another every seven minutes, eventually forming the back wall of what will be the first two-story, 3D-printed house in the U.S. 

It was an exercise in precision that Zivkovic, an architect and robotics expert, and a team of others have worked toward for a number of years. Under construction in an older, quiet neighborhood in Spring Branch Valley, this very modern home – embracing technology and building techniques still in their infancy – will look like nothing else in Houston.

MORE FROM DIANE COWEN: Architect Michael Hsu returns to Houston with thoughtful modern style

Zivkovic and Leslie Lok – a married couple who are also business partners in their HANNAH Design Office architecture firm in upstate New York – are assistant professors in Cornell University’s architecture school. Lok directs its Rural Urban Building Innovation Laboratory while Zivkovik directs its Robotic Construction Laboratory, two kinds of research that have come together in this new project in Houston, the city where Lok graduated third in her class from the former Robert E. Lee High School (now the Margaret Long Wisdom High School) before going on to Wellesley College and MIT.

The couple handled the design and project planning of this new 3D-printed house and worked with Houston-based PERI 3D Construction to develop the printing program. Another Houston-based firm, CIVE, handled the engineering and general contractor duties. 

Quikrete developed the commercial grade of concrete that is wet enough to be squeezed from the printer in ribbons, yet firm enough to hold their shape while drying.

Bing Tian, Quikrete’s director of research and development, said his firm spent five years working on a formula that would work with 3D printers. 
“Most people know Quikrete from buying bags of it at Home Depot or Lowe’s for DIY projects,” Tian said. “This is more like creating something that can be squeezed out of a tube like toothpaste. It has to be able to be pumped out and, layer by layer by layer, the density is still there. It takes a lot of chemistry to achieve that.”

In years of lab testing, they worked on mixes and practiced extruding it through remarkably low-tech methods.

“At the beginning we had no clue how to do it. We have no printer, so we couldn’t really test it. We bought a sausage gun and started from there – seriously, a sausage gun,” Tian said.

Quikrete’s first 3D house projects were with Alquist 3D, making two, one-story Habitat for Humanity homes in Williamsburg and Richmond, Va.
Yet another 3D printing company, ICON, is working with Mobile Loaves and Fishes on a 51-acre community of printed housing for the homeless in Austin. The first of its 400-square-foot homes finished in March 2020.

This home in Houston is for an unnamed homeowner, who’s purchasing the home for an undisclosed amount and has been involved in its creation as a homeowner normally would. It will be much bigger than others already built in the U.S., with 4,000 square feet in its two stories.

It will have some full walls of 3D-printed concrete along with a tall concrete chimney and other sections of the house that are also two-story, 3D printed. When the concrete work is done, the house will be finished with traditional construction methods to connect concrete portions, and for ceilings, some interior walls and finishes in rooms such as the kitchen and bathrooms.

The rippled edges from the layers of concrete printing will be left as they are – likely with a simple protective exterior coating – the material and its method of application both serving as part of the architects’ intended aesthetic.

MORE HOME DESIGN: Sugar Land empty nesters build dream home with indoor basketball court, lap pool and dog room

3D printing isn’t new; in their earliest stages, the printers seemed like expensive novelties that could replicate just about anything. Now, you can buy desktop 3D printers on amazon.com for $200 to $400, and use them for making everything from toys and product prototypes to even guns and gun parts, such as the Glock “switches” that made headlines earlier this year for their ability convert a semi-automatic firearm into a machine gun.

For the construction industry, 3D printers operate on the same concept, but are dramatically different – and much more expensive – machines. The PERI 3D printer being used on the Houston home is a huge structure with a frame that’s 40-feet by 50 feet and 30 feet high. It is run by a computer program that tells the machine how to execute the architects’ specifications. 

Concrete is mixed in a hopper on the ground before being pumped through a tube upward to where it’s extruded in ribbons about 2 ½ inches wide and ¾-inch high. Each ribbon of concrete adheres to the one before, leaving behind a ridged design pattern.

The home’s back wall – part of the living room – went up earlier this week, with pockets that will eventually hold shelves. Since each layer is just ¾-inch high and it takes the machine at least seven minutes to create a layer, this 22-foot wall will take more than 40 hours of printing to finish.

Another section of printing for the living room is already done, leaving an opening for a fireplace. In all, the house will take about 220 hours of concrete printing. The remainder of the work is expected to be finished by mid 2023.

In the course of creating the concrete sections of the home, the printer will be moved three times, Zivkovic said. Theoretically, the printing machine can operate 24 hours a day, though they’ve cut back to a handful of hours a day factoring in the heat for its human operators and the noise disruption for neighbors. 

Both Zivkovic and Lok said that 3D printing with concrete is the future of home construction. The massive printers are neither plentiful nor inexpensive, but in time they’ll multiply and get less expensive – as all high-tech products do.

As the cost of lumber and other materials becomes more costly and more difficult to get, concrete is a good replacement in Houston, since it is more durable and more resilient than wood, which can rot or succumb to termite or insect damage in our hot, humid climate, they said. It also stands up better to flooding and high winds.

Creating a two-story 3D-printed structure is more complicated than a one-story, and Lok said their goal is to perfect this larger structure and then scale up to create multi-family housing.

HANNAH Office Design, the firm that Lok and Zivkovic co-founded, also created the much-written about Ashen Cabin, a small, one-story cabin in New York that used concrete 3D printing for its base and was finished with slabs of wood from Ash trees infested with Emerald ash borer beetles – finding a productive use for trees that otherwise might have been cut down and burned – their destruction contributing to greenhouse gases.

Concrete itself is said to be responsible for 8 percent of all carbon dioxide emissions, according to a 2019 study by MIT, but Lok said that the precision of 3D printing reduces wasteful formwork. Without 3D printing, a concrete structure would be made of concrete blocks or by using molded forms that are filled with concrete and allowed to dry.

MORE FROM DIANE COWEN: After 9 years of saving, Houston woman completes dream remodel of Garden Oaks home

“It’s about how we can build differently and better for the future. The construction industry accounts for a big portion of the (world’s) carbon footprint,” Lok said. “We need to rethink how we use materials – that’s not just a social point of view, but a design point of view. How can we develop new materials and methods that allow us to build and think differently?”

The 3D printer also allows for more precise spaces, including the hollow cavities created for insulation or electrical and plumbing lines, said Lok, who with Zivkovic has been in Houston all summer preparing for the home’s construction. Lok will be here all of fall, as well.

“We’re still in construction, so I don’t know what the final cost will be,” Lok said. “Our focus was not to be the fastest or the most affordable construction. Our goal is to use it as a valuable learning opportunity to build good design and performance. The next step for us is to focus on the cost, the economy of the material and … see how we can reduce costs and make things more efficient.”

[email protected]

https://www.houstonchronicle.com/lifestyle/home-design/article/First-two-story-3D-printed-concrete-home-in-the-17441562.php