When it comes to building more housing, arguably the greatest obstacle is scalability. How can we build fast and efficiently enough to close the gap on the country’s housing crisis while not exacerbating existing issues concerning labor shortages, labor costs, and supply chains? If and when we begin to make up ground, how do we avoid flooding the market and creating another housing bubble? The answers to these and likeminded queries have eluded us.

For some, the answer—or at least a big part of it—lies with new technologies. Regional mass timber economies, volumetric modular construction, bio-based materials like mycelium and compressed earth, and mobile automated homebuilding systems are a few marquee examples.

Another is the growing trend of 3D printing. And one of the epicenters of this building segment lies in the heart of Texas.

Recent history

Back in 2019, Scott Gibson reported for GBA on Austin-based company ICON’s plans “to build a cluster of houses in an impoverished Latin American community” using its “gantry-style” Vulcan II printer that pumped out a material called Lavacrete at a rate of 5 to 7 inches per second. Gibson went on to highlight the apparent benefits and evident lack of publicized performance metrics of this endeavor, but remained optimistic, nonetheless.

The project in question, located in Tabasco, Mexico, and co-led by housing non-profit New Story and builder ÉCHALE, specified a community comprising 50 new homes for area families. ICON was contracted to build 10 of those homes—each 500 square feet and each printed in a span of 24 hours—which were completed in 2021.

A culture of leadership

ICON has been a leader and prominent voice in the 3D printing space for some time. In 2018, along with New Story, the young startup unveiled “the world’s first permitted, 3D-printed home” at SXSW. Since then, ICON has printed 150 homes and other structures spread across four U.S. states plus Mexico.

The company’s in-house design team has collaborated with the likes of Bjarke Ingels Group (BIG) and AIA Gold Medalist Lake|Flato Architects. It has worked with NASA on designs for commercial lunar developments and with BIG on a simulated Mars habitat.

Back on Earth, the company’s digital design catalog, Codex, represents a growing library of custom, ready-to-print home designs, including eight new exclusive homes planned for Wimberley, Texas.

According to Melodie Yashar, ICON’s VP of building design, everything in the Codex collection is “designed to achieve EnergyStar certification,” extending to appliances and EPA WaterSense fixtures. Meanwhile, ICON’s layered wall systems help “reduce energy consumption with above code minimum insulation” and increased thermal massing.

As for type, ICON is clearly open to designing market-rate housing. It would appear, however, that it wants to make a bigger dent in other markets. Judging by its long-standing partnership with New Story, whose mission is to “put vulnerable families on the path to housing” and land ownership, a big part of ICON’s focus is on building affordable and disaster-relief housing for communities in need.

New designs for affordable homes

Despite the company’s in-house design catalog, not everything at ICON is designed in house. In May 2023, ICON launched part one of its new two-phase design competition, called Initiative 99 (i99). The global competition called on students, architects, and other design disciplines to submit home designs that could be built for $99,000 or less using ICON’s proprietary printing technology and concrete mix design.

Submissions from more than 60 countries were received, with a select few in two submission categories—Professional and Student—advancing to the next round. In phase two, finalists were asked to adapt their designs for construction within Community First! Village, a master-planned community for the area’s chronically homeless, developed by local ministry Mobile Loaves & Fishes.

Last March, the winners of the inaugural i99 were announced, with two winning designs in the Professional category selected for construction at Community First! Village, set to break ground in early 2025. When built, the two structures will comprise four housing units and raise the total number of 3D printed homes in the development to 21, to date. A grant from Wells Fargo is pumping a half a million dollars to construction efforts.

Additionally, the top three winners in each of the two categories will have their designs included in ICON’s Codex catalog, and thus made available to any builder, developer, or home buyer who wishes to source a low-cost, ready-to-print home.

The winning submissions

The two designs set to start construction next year come from Brooklyn-based firm Guerin Glass Architects (1^st prize) and ConCave Studio, a global architecture collective led by Tara Bisharat. Guerin Glass’s sculptural designs resemble space-age “tiny” homes befitting a desert context. The rendered detailing is precise as well as economical. Barrel-sized masses of printed walls, with textured crochet-like patterning on the exterior, create a layout of soft edges and rolling contours, which are intercut by post-and-beam elements. Exposed particle boards for ceiling tiles, slab flooring, and a blend of modern but modest furnishings complete the proposed fit out.

ConCave’s design is a bit more polished, literally. Polished floors, natural wood paneling, and recessed lighting give the studio’s proposed interior a high sheen, while an irregular–pitch roof design seems both playful and practical. The printed super structure provides a subtle contrast to these qualities. A simple pattern of “poured” concrete is identical for both the outer and inner shell, lending these façades a tactile earthen quality, like layered strings of bleached mud.

In both instances, the design teams demonstrate a clear understanding of ecological context, site constraints, and climate zone requirements. Orientation, materials selection, and glazing design were clearly considered to optimize daylighting and passive cooling.

Working with low-carbon materials

ICON has moved on from Lavacrete, its original building material. After two years in the lab, the company recently unveiled “a new low-carbon extrudable/printable concrete formula” called Carbon X, which the company says represents a 42% carbon reduction on “our previous iteration of printed materials.” Unsurprisingly, Carbon X will be the applied building material for the new builds in Community First! Village, and presumably for all near-future builds.

The mix design for this product reduces the required cement content and cuts down on transportation-related emissions by locally sourcing cementitious materials from the South Texas region. According to internal figures provided by ICON, nearly 50% of the cement is replaced with supplementary cementitious materials (SCMs), along with “a high portion of aggregates.”

“For context,” the company’s statement continues, “the average cement content of a 3D-printed mix design is roughly 1000 lb./sq. yd. Carbon X has 516 lb./sq. yd. The mass ratio of aggregate to binder in an average 3D–mix design is 1.5. Carbon X’s is 2.7.”

Carbon X is “the lowest carbon residential building system ready to be used at scale,” Yashar says. In a worthwhile effort to back up this rather bold proclamation, ICON recently partnered with the MIT Concrete Sustainability Hub on a white paper, published last March, that breaks down and analyzes the life-cycle performance of 3D-printed homes compared to conventional stick-frame homes.

How they got here

Early on, the authors concede the controversy surrounding the carbon intensity of 3D-printing mixtures. Concerning some older 3D printing solutions, they write: “Owning to small maximum aggregate size and specific rheological requirements, the binder content of 3D print mixtures is reported to be larger than conventional concrete and consequently, result in substantial carbon footprints.”

ICON wished to provide a first-of-its-kind analysis of the embodied carbon intensity of 3D-printed homes based on existing builds in the U.S. And they wanted to use their own work— proprietary printing mix, wall system details, and printing robot—as the guinea pig.

The bill of materials and embodied carbon estimates were calculated using Tally software, a Revit plug-in for performing whole-building life cycle assessments (LCA). The distances between raw material suppliers and the dry–mix batch plant were critical data points as well. The resulting LCA indicates that the embodied and operational impacts of ICON’s homes—even accounting for a “custom concrete mix” (Tally does not allow separate embodied carbon calculations for specific admixtures)—were still several percentage points lower than stick-framed homes.

Provided ICON’s specific solution can be deployed at scale, even on a regional level, then this emergent technology holds real promise for closing the gap on the country’s affordable housing crisis. Only time will tell. And robots. Lots of robots.

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