Author(s): Angelo Verzoni. Published on March 1, 2019.

Outside the Box

The increasingly popular option of modular construction offers innovative and efficient solutions for designers, builders, and owners. But questions persist on how the industry should be regulated.


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ON A RAINY DAY in Seattle this winter, construction workers stood on a rooftop seven stories above the South Lake Union neighborhood in the city's downtown. Above them, a crane gently lowered a shipping-container-sized rectangular box toward the roof. The workers shuffled around, tugging on ropes connected to the box, guiding it into place until it plunked snugly amid stacks of identical boxes. It was the last of 228 modular units, or modules, to be connected to make Seattle’s new 264-room citizenM hotel.

Throughout the United States, modular construction—where box-like modules are fabricated offsite before being transported to a construction site, where they’re stacked together like Legos® to form a full-sized building—is becoming more popular. The technique isn’t new—it’s been around for decades, but has been used primarily for small residential construction projects, like one- and two-family homes. What’s changing is its use in much larger and more complex projects as modular buildings become bigger and taller. Already a staple in European countries, the US is now home to a rapidly increasing number of modular hotels, high-rise residential buildings, offices, and health care facilities.

That increasing popularity in the US is helping drive modular's global growth. Modular construction is a $112 billion industry worldwide, according to Construction Dive, a construction industry news and analysis website, and is projected to hit $160 billion by 2023, with an annual growth rate of nearly 7 percent, compared to about 5 percent for the construction industry overall, according to industry sources.

“We’re seeing more because of owners’ willingness to utilize the process,” Tom Hardiman, executive director of the Modular Building Institute (MBI), an industry trade group, told Construction Dive. That willingness is driven by an array of factors, including a lack of skilled labor in the traditional construction sector, a lack of affordable housing, rising and unpredictable materials costs, and the constant pressure to deliver on time and on budget. Modular construction, Hardiman said, “addresses many of these needs for the owner.”

The boom in bigger and taller modular buildings in the US has prompted some fire and life safety professionals to raise questions about how the industry is regulated, such as how the units are inspected at off-site fabrication facilities and how final assembly takes place at construction sites. If modular units are made in North Carolina or Ohio or Maine for a building under construction in New York, for example, how is coordination handled among states to make sure the components comply with applicable codes?

In interviews with NFPA Journal, those with experience working with modular construction—both industry insiders and authorities having jurisdiction (AHJs)—answered that question and more. They paint a picture of an industry that is better-regulated than one might think, but one where there is still room for improvement when it comes to regulation—namely, through standardization.

There’s currently no information specific to modular construction included in NFPA codes and standards, but a number of NFPA documents have already been identified as places where that information could end up in the future, including NFPA 5000®, Building Construction and Safety Code®, and NFPA 101®, Life Safety Code®.

“If the modular industry could set a standard, I think every state would go with it,” said Tim House, a Kentucky state building official who has experience with modular construction projects. Either way, he said, AHJs around the country are “going to have to accept” modular construction—it’s only going to become more common and more ambitious.


Years ago, a building built in Seattle was just that—a building built in Seattle. But it was a different story for the citizenM hotel project.

The creation of that building began with the fabrication of 228 separate modules in a factory in Poland. The modules were then shipped over 9,000 miles, via the Panama Canal, to the Port of Everett, Washington, and trucked 30 miles to the construction site in Seattle's downtown, according to an article in Building Design + Construction (BDC) magazine.

Infographic on the modular construction industry worldwide and its projected rise

CitizenM, a hotel chain based in Amsterdam, has used the same Polish fabrication factory to build modules for its hotels around the globe; according to the BDC article, the company is planning a big push into the US market this year, with several more modular hotels planned from Boston to Los Angeles. In September, citizenM opened a hotel on Bowery Street in Lower Manhattan—at 21 stories, it’s the tallest modular hotel in the country.

For that project—and other modular construction projects in New York City—local code officials had to approve the Polish fabricator as a contractor to ensure that even though the modules were being built thousands of miles away, they would comply with New York City codes, such as requiring automatic fire sprinklers and exit signs illuminated by an emergency power source. “They had to submit their quality control procedures to the city,” said Mike Schwartz, a senior associate at DeSimone Consulting Engineers, the structural engineering firm for the citizenM Bowery project. “It was definitely a process that took time, but I think the team did a good job of planning ahead, and the city seemed receptive to it.”

New York City is home to a number of modular buildings, including the world’s tallest such structure, a 32-story residential property that opened in Brooklyn in 2016. The approval process for modular unit fabricators is defined in the New York City Building Code and regulated by the Office of Technical Certifications and Research. The process outlines steps for sending New York City inspectors to the site where modules are being built to inspect them, but it also allows for approved fabricators, who may be located as close as New Jersey or as far away as another continent, to self-inspect their work, and for a third-party registered professional to sign off on it before it’s transported to the construction site. Once there, city inspectors oversee the final steps such as connecting the plumbing, fire protection, and electrical systems from module to module.

While the permitting and inspection process for modular buildings is codified in New York City, it’s possible that a modular project could occur in a local jurisdiction that doesn’t have a modular building regulatory system in place. The regulatory responsibility then falls, in most cases, on the state, according to Hardiman. “[Thirty-five] states have a statewide administrative agency that oversees the modular building industry,” Hardiman said in emails to NFPA Journal. “That agency either has a staff of engineers or contracts with independent, third-party engineers for a variety of functions. These engineers are responsible for inspecting plants and plans, quality control process review and inspections, and ultimately deeming that the building component or module will meet the codes at the final destination. A vast majority of the time, these inspectors are visiting manufacturing plants nearby (within 500 miles). But on occasion … engineers are required to travel oversees for the plant inspection and quality control or quality assurance. A best practice is to be in regular communication with the local AHJ during the process.”

Dale Stern, an architect at MGAC, a national construction management consulting firm, equated the permitting process for each module to “getting a UL sticker on a product,” according to a blog he wrote for his firm’s website. “This is because once the units are brought to the site, they’re fully enclosed, so a building inspector can’t simply look inside the walls to see how the modules have been put together,” Stern said.

The process doesn’t sit well with some AHJs, though, who can feel like they’re too far removed from a project, said Jon Laux, community development director with the Twin Falls County (Idaho) Planning and Zoning Department. In 2017, an assisted living facility that was built using modular construction opened in Twin Falls, and the state of Idaho was responsible for regulating its construction. “Because it’s not your eyes that are on it, you have to put your trust in another jurisdiction,” Laux said. Rumors can fly that “some things aren’t looked at as thoroughly as needed,” he said, because the modular construction process is so fast compared to traditional construction—many estimates say it cuts construction time in half.

But once potentially wary AHJs learn more about the process, Laux believes they will be more comfortable with it. “All those pods are being cranked out down an assembly line, so you can get a little concerned not being a part of that,” he said. “That’s probably from a lack of a full understanding of the process and watching it progress, so there are some assumptions unfortunately that can be made.”

Construction workers work on a individual module in a warehouse

Making it Modular In the typical modular construction process, individual modules are fabricated off-site, sometimes in a different country. Photograph: Getty Images

Likewise, House, who is deputy commissioner of the Kentucky Department of Housing, Building, and Construction, said the biggest issue surrounding modular construction and its regulation is a “lack of knowledge.”

“If building officials and fire officials could actually go to a [modular fabrication] plant and see the process from the first stick of wood to the finished product, I think most of everybody’s angst would go away,” he told me. “Because if you really think about it, in a modular plant all the building material never sees a bit of rain or a bit of snow. It’s always climate-controlled. You’re not going to get that on a construction site … There’s more quality control in a modular plant than there is out in the dirt, so to speak.”

In the 15 states that lack state agencies to regulate modular construction, the AHJ typically takes sole responsibility, Hardiman said. While that may alleviate concerns like the ones Laux pointed out, it may also be overwhelming for them to staff the floor of a fabrication area, especially when it’s located hundreds or even thousands of miles away. “You’d have to be staffing those places with the proper inspectors, and that’s a big burden for an AHJ,” Laux said.

The answer to that problem may already be here, though: remote video inspections. That’s how it’s done in Kentucky, House said. “In the past, any modular construct in Kentucky had to have an inspector sent to the plant whether it was in Florida or Texas or Indiana or Ohio,” he said. “But over the years we’ve been able to use third-party inspectors and we’ve been able to use video inspections … We’ve been using everything from Skype to FaceTime.”

In August, NFPA published a white paper titled “Conducting Remote Video Inspections” that concluded remote video inspection “offers both jurisdictions and permit holders the opportunity to use technology to increase the efficiency of the inspection process, which has the potential to benefit both.” But it also comes with potential limitations and risk, the paper said. Five months after the paper’s publication, the NFPA Standards Council approved a project to develop requirements for the performance and use of digital video, photographs, audio, and other methods to conduct remote inspections of buildings or building systems. Applications for the technical committee for that project closed in February, and a preliminary committee roster will be presented to the council in April.


Advocates of modular construction are quick to point out its benefits. There’s the increased speed of construction and the promise of cutting costs. There’s the sense of control gained from building the modules indoors, where rain or snow can’t hinder the process. But there are also potential benefits that relate to fire and life safety. An estimated 80 percent of the built environment in developing nations lacks codes and standards, and therefore lacks qualified code officials, according to experts from the World Bank Group, who were interviewed in October for an NFPA Journal article on fires in shantytowns. Bringing a large part of the construction process for projects in these places into a better-regulated environment, overseen by qualified professionals, could translate to safer buildings, experts say.

Different types of modular buildings

Clockwise from top left: Modules are then shipped to the contruction site, where they are placed by a crane, often around a concrete tower for support. Locally certified workers connect the modules, as well as the plumbing, fire protection, and electrical systems. As a final step, exterior wall assemblies are often placed on the buildings to enhance their appearance. Photograph: Modular Building Institute

In 2016, for example, the hotel developer Hilton announced it had built a 280-room modular hotel in the African nation of Ghana. “The option to go modular and improve on room quality, project delivery, and [the minimizing of] construction risk was warmly embraced by our development, design, and construction teams, and we feel it is the future of the industry,” a project official said in a statement released after the hotel opened.

In China, modular construction promises a “significantly more stringent multistep inspection process than traditional builds,” according to an article published on, an international prefabrication industry website.

By its nature, modular construction also reduces the amount of construction site activities like hot work and the accumulation of combustible waste at those sites, both factors that can lead to catastrophic blazes. From 2010 to 2014, an average of 3,750 fires in buildings under construction occurred in the US each year, according to NFPA data. Those fires caused an average annual $172 million in direct property damage. It’s a huge, costly problem—and one that modular construction might help fix. A study published in 2012 in the Journal of Architectural Engineering found that for three modular construction projects—buildings measuring 12, 17, and 25 stories in height—on-site construction waste was reduced by 70 percent.

Exterior of a modular constructed building in Brooklyn

New York City is home to a number of modular buildings, including the world’s tallest such structure, a 32-story residential property that opened in Brooklyn in 2016. Photograph: Griss

While most people who have experience with the modular construction industry, like Laux and House, seem to be comfortable with its current regulation, there is still room for growth. “The biggest challenge is finding a way to inform code officials of what goes into [modular construction],” House said. Incorporating additional language on modular construction into widely used codes is one possible way of achieving this.

Hardiman said the MBI is currently working with the International Code Council (ICC) to develop a series of “resources, tools, and code language” pertaining to the regulation of modular construction. “We were successful in the 2018 [International Building Code] in getting standard language included for the approval process for modular ‘relocatable buildings,’” he said. “We want to expand upon that effort and create a standard process for approval of all modular buildings. That’s a bit of a longer-term project but we plan on working with ICC this year to get it off the ground.”

Additionally, House suggested the creation of other educational materials, like video trainings, which could come from an organization like NFPA. “I think virtual training could solve a lot of concerns,” he said.

Regardless of how modular construction stacks up to traditional construction through the eye of a public safety professional, House said “[AHJs] are going to have to accept it” one way or another because the trend isn’t going away. “We’ve told all our inspectors, ‘You’re going to see a significant increase in modular construction in 2019 and another significant increase in 2020,’” he said. “Due to a lack of manpower in the traditional construction industry, modular is one of the few ways you’re going to be able to meet construction deadlines in the future.”

ANGELO VERZONI is staff writer for NFPA Journal. Top Photograph: Modular Building Institute