Printing Buildings

3D printing is now being used to construct full-sized, fully functional houses, offices, and other buildings. As the industry gears up for a rapid expansion, guidance is needed to ensure that these structures are safe.


It’s a weekday afternoon in January, and I’m standing on a landing in Boston’s Autodesk Technology Center, an architecture and engineering R&D workspace housed in a cavernous industrial building in the city’s Seaport district. I’m joined by Anna Cheniuntai, who along with her husband, Nikita, cofounded a company called Apis Cor, which is a resident of the Autodesk facility. Together, we gaze down on a device that Cheniuntai describes as “the future of construction.”

The machine below us is an oversized 3D printer that can build entire structures spanning thousands of square feet and multiple stories. It consists of a stocky circular base supporting a complex extendable arm with a nozzle at one end. The device is designed to feed concrete and other materials through the extendable arm to the nozzle, which then applies the mix in thin layers as the arm is guided by special software — essentially a giant robotic caulking gun. It’s powered off at the moment, but it’s easy to imagine it hard at work, depositing layer after layer as walls, then rooms, then an entire building takes shape.

Nikita completed a design of the machine in 2016, and Apis Cor was founded the same year. A month before I visited the Apis Cor offices, the company made industry history by completing the world’s largest structure to be 3D printed entirely on site. The two-story building, in the city of Dubai, in the United Arab Emirates, spans 6,900 square feet and houses administrative offices for the city’s government.

Cheniuntai isn’t alone in envisioning a future full of 3D-printed construction. Her company is one of several that are already using 3D printers to construct houses, office buildings, and other structures worldwide. Dubai, which is known as a global leader in construction innovation, has set a goal of having 25 % of its new buildings 3D printed by 2030. “This technology will create added economic value and benefits worth billions of dollars during the coming period,” the government-run Dubai Future Foundation says of the objective.

Other construction industry experts see 3D printing, also known as additive manufacturing, as a potential solution to the challenge of affordable housing worldwide. “With 3D printers we can build faster and cheaper,” Cheniuntai says. “We believe we can replace some portion of single-family homes constructed with masonry. It will be the new way of building.”

But as the possibilities of 3D printing in construction surge around the world, so does the need for safety guidance for these new structures and the processes used to create them. That applies to authorities having jurisdiction (AHJs) as well as companies like Apis Cor, both of whom must ensure these structures are safe during fires and natural disasters and that they meet widely used building codes. That’s where organizations like NFPA, the International Code Council, and UL can help. UL has already released a document that provides the framework for evaluating and approving 3D-printed buildings, and experts say they hope it’s the start of more code language and other resources related to 3D-printed construction.

“The biggest challenge for code officials right now is figuring out how to evaluate these buildings,” says Howard Hopper, a global regulatory services manager at UL. “Even officials who haven’t encountered this in their communities know they’re going to face it soon, and there’s going to be strong pressure for them to approve 3D-printed buildings due to affordable housing considerations. Right now, for the most part, they do not have technical expertise or experience in evaluating 3D-printed building construction, and are looking for more information on evaluating this technology in codes and standards.”

Why 3D?

The world’s first fully 3D-printed building is said to be the 3D Print Canal House in Amsterdam, which opened as a research and design project in 2014 and remains accessible to the public to tour as an attraction. Research and development into the use of 3D printers to make entire structures dates back to the late 1990s, when developers realized the technology, which had been used to make architectural models of structures, might have the potential the create the actual buildings.

Since the Canal House was completed, developers have made significant technological strides toward creating fully functional 3D-printed buildings, and that progress has resulted in an industry poised to explode. A report released in September by market research firm MarketsandMarkets estimated that the 3D-printed construction industry will grow from a roughly $3 million industry globally today to a $1.5 billion industry by 2024. Much of that growth will occur in the Asia-Pacific region, the report says.

Building-scale 3D printing is based on the same general concepts as other forms of the technology. Like desktop 3D printers made by companies such as MakerBot, 3D printers designed to print buildings or building components are programmed to assemble structures in a virtually endless number of configurations. Most often, these 3D printers, which usually stand no taller than a pickup truck, use concrete to build the structure, extruding the paste-like substance in layers that quickly harden to form walls. But an array of materials, including plastics, metals, and even living organisms, can be used to print buildings and building components (see “Beyond Concrete”).

In 2015, WinSun, a Chinese construction technologies firm, used large, 3D-printed components to piece together a five-story, 11,800-square-foot apartment building, which still sits on display alongside a neo-classically designed mansion constructed in the same fashion by WinSun at an industrial park near Shanghai. Both are model structures that aren’t actually being used. At the time, the idea of 3D-printed buildings was so far-fetched that some people thought the news being reported out of China was a hoax. But a year later, the world’s first 3D-printed office space opened in Dubai. And in 2018, a French family of five became the first people to move into a 3D-printed home.

The industry made a number of notable strides in 2019. In July, the world’s largest single-family home to be 3D printed entirely on-site was completed in Patchogue, New York, on Long Island. It measured about 500 square feet, or just under double the size of the average hotel room. In October, ICON, a construction technology firm in Austin, Texas, built a 3D-printed house that was the first in the United States to receive a construction permit. In December, ICON also completed construction of a number of 3D-printed homes in an impoverished neighborhood in Mexico, and Apis Cor completed its Dubai project.

The benefits of 3D-printed buildings are obvious, especially as the world grapples with crises like homelessness, poverty, and affordable housing. Companies like ICON have touted their ability to print homes for $4,000 or less — not counting costs for wiring, plumbing, roofing, and so on — in less than a day. Those upsides are particularly attractive for developers looking to build in remote or impoverished areas, regions that could benefit from new approaches to building affordable, standardized housing. An estimated 1 billion people worldwide live in informal settlements, where homes and other structures are not built to any code. Often, residents use items like plastic tarps and cardboard boxes to construct makeshift homes in these communities, which are plagued by massive, deadly fires.

A 2018 article by Manufacturing Tomorrow, a manufacturing industry news website, observed that “there are many people for whom decent housing is still a luxury. A 3D printer can help solve this problem … especially in developing countries.” The article added that, while the technology “might have some way to go when you compare traditional means of housing, it is a much sturdier option than lean-tos.”

Some observers say 3D-printed buildings may provide the answer to humans inhabiting outer space, too, and there are companies that have already won awards from NASA for their work on these kinds of projects. Last year, NASA awarded $500,000 to AI SpaceFactory, a New York City–based design and architecture firm, for designing a home astronauts could 3D print and live in on Mars. The structure would use materials made from Martian rock, eliminating the need to send materials from Earth — 140 million miles distant.

‘Totally outside the code’

As with any new technology, 3D-printed construction has raised questions over how it performs compared to traditional construction materials and methods: Will a 3D-printed home last as long as a traditionally built home? Will it be structurally sound and safe in the event of a fire or natural disaster? Since the development of the technology has outpaced updates to widely used codes and standards from organizations like NFPA and the ICC, it has left builders and AHJs with few sources for answers.

“If someone wants to build a building in the US, or anywhere in the world, they go to the building code and say, ‘OK, here are the requirements for building a wood, concrete, or steel structure,’” Hopper says. “But if you’re trying to use nontraditional construction materials and methods, there are no requirements in these codes.”

“Building codes and regulations are about something you build the same way, all the time,” Cheniuntai says. “With masonry, for example, there are only a few configurations, and all of them are tested and certified and documented. There are building codes that provide the rules, but there is nothing like that for 3D printing.”

For AHJs, one of the biggest concerns surrounding 3D-printed construction lies in the fact that things can change at any moment. The blends of materials being extruded by the printers, for example, can change as companies continuously work to improve their formulas, which are often proprietary and adapted to local conditions. Apis Cor spent time experimenting with its mixture of materials before finding one that would be able to withstand the extreme desert heat of Dubai, according to Cheniuntai.

“Traditional materials like wood and steel have characteristics that are inherently known,” Hopper says. “Materials such as wood or vinyl siding, for example, are required to comply with industry standards and have a history of durability when exposed to the elements — they aren’t going to disintegrate in a year. The materials used in 3D-printed construction and the 3D-printing methods used to form building assemblies have unknown characteristics.”

Concrete and concrete-like materials have most often been the materials used in high-profile projects like those spearheaded by Apis Cor and ICON, but Hopper says he is also aware of 3D-printed building assemblies made with thermoset composite materials — mixtures commonly based on glass or carbon combined with a resin.

In addition to unknown material mixtures, the 3D printing process and the configurations with which the walls of 3D-printed structures are built can also change, and that can influence structural integrity as well as smoke and flame spread. While concrete is a familiar material, for example, the 3D printing process can render it almost unrecognizable in terms of its characteristics to architects, engineers, and code officials, says Benton Johnson, a structural engineer at Chicago-based SOM. The global architecture and engineering firm has worked on 3D-printed construction projects for the US Army Corps of Engineers. “Although the materials can be commonplace, like concrete, the technique results in something totally outside of the building code,” Johnson says. “You can use a 3D printer to create hollow wall structures … without perfect bonding between layers.”

It’s for reasons like this that Johnson, along with his colleague, SOM architect Lucas Tryggestad, tell me that they think 3D-printed buildings are still a ways out from becoming viable alternatives to traditional construction. “I don’t think the technology is there yet, nor is the comfort level of utilizing it,” Tryggestad says. But both Johnson and Tryggestad say there are a lot of reasons 3D-printed construction should and will become common in the future, such as the creative freedom it gives architects and the speed with which projects can be completed.

Once 3D-printed structures are built, more challenges can emerge as designers work to convert the concrete boxes into livable space. Beth Culver, a building code official in Austin, Texas, says that some designers don’t know what to do when faced with the concrete walls of 3D-printed buildings. It was her department that last year became the first in the US to approve a 3D-printed building, the project undertaken by ICON. “Where do you put the plumbing? Where do you put the electrical?” Culver says. “Because of the nature of this construction, a lot of things have to be surface-mounted on the interior.” The city also found the ICON building to have insulation issues, Culver adds, and officials made an exception in approving it despite the structure not meeting local energy codes.

Despite these challenges, Culver says Austin officials are still proud to embrace this new technology because they understand its potential to address challenges like affordable housing, an issue that she says her colleagues regard as a public safety problem in its own right. A tragic example was the Ghost Ship, an improvised live/work space that occupied a warehouse building in Oakland, California. Faced with increasingly unaffordable housing in the city, a collective of artists and others had illegally moved into the building, which lacked basic fire and life safety protections. In 2016, a fire in the building killed 36 people.

“We’re very open to the technology becoming more prevalent in Austin,” Culver says of the 3D promise. “We’re willing to work with developers.”

The path forward

Very little research has been conducted to determine which materials and configurations are the safest for 3D-printed buildings. A 2018 study published by researchers at Poland’s AGH University of Science and Technology analyzed 3D-printed construction materials from a Russian company called RENCA, concluding that its proprietary concrete-like material, known as Geocement, was fire-resistant and had high compressive strength. Other studies, however, suggest 3D-printed concrete assemblies are weaker than walls built with traditional materials. “There are some issues and limitations associated with 3D printing such as the low stiffness and strength of the printed building materials,” observed a 2019 study published in the journal Frontiers in Built Environment.  Because of this lack of research, Apis Cor and other companies have been taking it upon themselves to conduct tests on their materials and designs. A goal for 2020, Cheniuntai says, is for Apis Cor to find a consistent approach — materials and a design it uses in every project — that would lead to AHJ-approved buildings. “We’re developing a design for a wall structure that we’re going to test, certify, and use all the time, so that building officials will know this has been tested and is safe,” Cheniuntai says.

The idea is that AHJs would then be able to approve the structures based on the alternative materials and methods provisions of codes like the IBC and NFPA 5000®, Building Construction and Safety Code®. Cheniuntai says the company’s preliminary testing has shown its 3D-printed walls have greater compressive strength than traditionally built walls. “It proves we’re in the right position, and we can move forward,” she says. Apis Cor has yet to conduct fire tests on its materials and configurations but plans to over the next year.

Culver says the approach Cheniuntai describes is one that officials in Austin would be open to. “As long as somebody is providing test data and information for us to evaluate, we would do that in conjunction with the Austin Fire Department,” she says.

This past fall, UL published UL 3401, Outline of Investigation for 3D Printed Building Construction, which can be used to evaluate the printer, fabrication process, and materials used to verify that they consistently produce building elements with the same properties. Builders can use the document to create a report of findings, Hopper says, showing AHJs that their building assemblies comply with relevant codes and standards like UL 263, Standard for Fire tests of Building Construction and Materials, and NFPA 275, Standard Method of Fire Tests for the Evaluation of Thermal Barriers. “This report provides AHJs with the technical information they need to inspect and approve 3D-printed buildings under the alternative materials and methods code provisions and will in turn speed up the approval process,” he says.

UL, along with support from several building code officials in the US, was successful in getting UL 3401 referenced in the 2021 edition of the International Residential Code, Hopper says, and he’s optimistic that similar language related to 3D-printed construction will be added to other codes in the future.

Tracy Vecchiarelli, a principal fire protection engineer at NFPA and the NFPA staff liaison to NFPA 5000, agrees. “As technology improves and construction methods evolve, our codes have to keep up,” Vecchiarelli says. “I expect to see this type of construction make its way to our technical committees and eventually into our codes.”

At least one company in California is already using UL 3401. Mighty Buildings, a 3D-printed construction company in the San Francisco Bay area, recently became the first such company to achieve UL coverage of a building assembly based on that document, says Sam Ruben, the firm’s vice president of compliance, sustainability, and partnerships. Like Apis Cor, Mighty Buildings has conducted a number of tests to make sure its materials and configurations are safe, observing protocols in UL 723, Standard for Test for Surface Burning Characteristics of Building Materials, and NFPA 286, Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth.

“So far it’s performed quite well,” Ruben says. Mighty Buildings is perhaps the only 3D-printed construction company out there whose material, a nonconcrete thermoset composite material, cures so fast and hard that they can build roofs with it. “We’ve developed a unique material that cures quickly enough that it can support its own weight,” Ruben says.

Safety, he adds, has always been at the heart of what the company does. “We’re building places for people to live,” he says. “It’s not like developing software where you can throw it into the wild and debug it later. So we had to do it right from the beginning. We want to make sure 3D printing is able to live up to its promise in the construction industry in a way that’s safe and standardized.”

ANGELO VERZONI is staff writer for NFPA Journal. 

Reprinted with permission from NFPA Journal (Vol. 114, #2) copyright © 2020, National Fire Protection Association, Quincy, MA. All rights reserved.