I stayed overnight in a 3D-printed house in Austin, Texas. Here’s what I learned about this construction method.
by Belinda Carr
- 3D homes’ charms different from those of stick-built homes
- However the technology is new and some details still need ironing out
- Manufacturers have yet to explore the 3D printing’s true design potential
ICON is one of the most recognizable names in the 3D-printed concrete business. Their highly publicized East 17th Street Residences in Austin, Texas are finally complete and I stayed overnight in one of them.
In this article, I share what I learned from that visit, including my impressions of the architecture, the interior design and the air quality.
3D Printing
ICON’s four houses are in a rapidly growing neighborhood in East Austin. They were designed by Logan Architecture and the property developer was 3Strands.
Only the first floors of ICON’s Austin, Texas homes are printed. The second floors are wood framed with metal siding.
Once the concrete foundations were in place, the walls were printed with ICON’s Vulcan printer, which lays down 1-inch thick, 2-inch wide beads of concrete at a rate of five to seven horizontal inches, per second. Exterior walls have two layers separated by a foam insulation core, while interior walls have just one layer.
All the starts and stops of the concrete layers are hidden behind window and door openings. Excess concrete was used to make sloped lintels and frames for the windows.
The concrete used in 3D printing isn’t actually concrete: it’s a proprietary cementitious material called Lavacrete that doesn’t contain gravel or coarse aggregates. I’m not sure how strong Lavacrete is, because one page of ICON’s website says that it has a compressive strength of 6000 psi, while another page says that it is a more reasonable 2000-3500 psi.
Concrete walls, as well as door and window frames, were coated with a white elastomeric paint, which is flexible and watertight when dry, and which bridges non-structural hairline cracks. I couldn’t find any visible cracking on the exterior or the interior.
The layers are mostly even but bulge out at window and door frames because the gantry—the overhead structure that supports the printer—tends to wobble at turns. There are also gaps where the concrete meets windows, doors and other elements. ICON decided to embrace these imperfections rather than trying to “fix” them. That’s the reality of 3D printing right now—it’s not perfect.
Only the first floors of the four houses have concrete printed walls; the upper floors have traditional 2×6 wood framing. But of course walls are just part of a building. Even though it took five to seven days to print the first floor of each these houses, installing all the utilities and finishing the exterior and interior took several months.
Exterior
The use of color on the exterior of these houses is very successful. The horizontally striated concrete printed walls on the lower level are painted white. The wood construction on the upper level is clad in vertically striated, black metal paneling. This draws your eye upwards and makes the building seem taller than it is. The wood walls overlap the concrete walls. This makes for a clean transition and a clear distinction between the two methods of construction.
The designers used rounded edges on the lower level, while building 90-degree corners and a traditional pitched roof on the upper level. It makes the building look top-heavy, and gives the illusion that it’s actually a black house floating over the base.
Lastly, every one of the four houses is slightly different, some have red cedar siding, and some have black siding. Their orientations and the locations of their entry doors are different, too. It keeps you interested and looking around for more variations.
As you can probably tell, I found the architecture inspiring and successful.
Interior Layout
The unit that my husband and I stayed in had a half bath, a kitchen and a living room on the lower level. Upstairs, two bedrooms are separated by a full bathroom.
The interiors are clean and minimalist. Interior designer Claire Zinnekar went for a “West Texas” vibe, with muted colors and simple patterns. I call it “Marfa chic,” because it reminds me of the somewhat quirky West Texas town.
The architects had to find creative ways to hide electrical wiring, plumbing and vents. In the kitchen, they framed out part of a concrete wall and ran the utilities through it. Unfortunately, the kitchen cabinets are set up against one of the 3D-printed exterior walls, which could make remodeling difficult in the future.
Although the exposed printed concrete can look rough, the home also has super smooth drywall interior partitions. The bump out where the peninsula meets the exterior wall is a utility chase.
How best to integrate electrical wiring and devices into 3D-printed walls remains a challenge. For instance, because the concrete wall is uneven, some of the wall plates are loose.
How do you hang pictures on a concrete printed wall? ICON’s solution is to attach sleek picture rails where walls meet ceilings. Frames are hung from transparent plastic cables.
Insulation
One big advantage of concrete construction over stick framing is that the house is naturally quiet.
Even though the wind was howling outside, the interiors were wonderfully quiet thanks to the thermal mass of the concrete, as well as the open cell insulation between the two layers.
There’s also very little thermal bridging through the concrete walls. That’s because, apart from the door and window openings, the inner and outer wall layers never meet.
I used a FLIR thermal imaging camera to see if there was any heat loss or gain through the walls. The living room downstairs was very well sealed and I found no obvious leaks at the base of the walls, the ceilings, or even around windows. However, there was some thermal bridging through the wood studs upstairs, which is typical.
Positive Energy designed an ERV or Energy Recovery Ventilation system for every house. It brings in fresh air continuously at a rate of 70 cubic feet per minute. An Air Handling Unit circulates this fresh air throughout the house. The ERV means that the bathrooms don’t need traditional exhaust fans.
The engineers at Positive Energy are fully confident in the sizing of the ERV system. However, my husband, myself and a neighbor, Jarret Gross, had dinner together in the living room, my Airthings sensor said that the CO2 levels spiked. They remained elevated throughout the night. I was there for less than 24 hours, and the sensors take at least a couple of days to calibrate, but it’s something I’m concerned about with airtight homes.
Now for the question everyone asks: how much do these homes cost? All four units have been sold for the following prices:
2 bedroom, 1.5 bath, 1,106 sq. ft.: $450,000
4 bedroom, 3 bathroom, 1,521 sq. ft.: $745,000
4 bedroom, 3 bathroom, 1,928 sq. ft.: $795,000
These prices are comparable to other properties in the area.
Conclusion
Those of you who follow me on YouTube, or who read my article in last month’s issue, know how cynical I am about the claims made by the 3D-printed concrete industry, but these houses really impressed me.
The project is refined and well thought out. The people at ICON obviously take pride in these homes and want the inhabitants to feel that same sense of pride as well. They even embedded a medallion at the entrance to the home, which says the home was designed with love in Austin, Texas. The name of the printer used and the building number is also on it.
But, as much as I loved the architecture and site layout, I was disappointed that they printed mostly straight walls rather than exploring the three-dimensional capabilities of the technology. These homes could have been made with CMU block walls or precast panels (although they wouldn’t be as enticing as 3D-printed walls).
However, ICON seems to be pursuing refinement and economies of scale rather than design exploration. That makes sense as a business strategy, since they are reportedly planning a community with a big national developer.
Although I hope to see improvements in the consistency and smoothness of the printing process, I can see this project becoming an “historic home” in 50 to 70 years from now. I’m very interested in seeing how these and other 3D-printed concrete homes hold up over time.
I’ve posted a video about this project on my YouTube channel:
If you have any questions about the project, feel free to leave a comment below that video.
Belinda Carr is a Dallas-based building science researcher and content creator. Find her at YouTube.com/BelindaCarr. All photos by the author.
