Buildings editor Nadine M. Post's recent cover story, "The Promise and Pitfalls of Modular Buildings," and related articles, "Mortenson Uses Off-Site Construction to Speed Denver Hospital Delivery," "Project Frog's Kit-of-Parts Approach Allows Better Design by Avoiding Trucking Limits" and "Despite Challenges, Developer of the Stack Thinks Modular Is the Way to Go," attracted a number of comments and kudos. The letters follow:

Call for Less Cheerleading and More Critical Observation

The modular sector needs less cheerleading and more critical observation, so I thank ENR for publishing this well-researched and informative article.

Despite the challenges, the reason the modular sector will continue to grow is because a well-organized plant is a much more productive work environment than a construction jobsite. Combined with the fact that per hour, labor on jobsites is more expensive than shop labor, firms with prefabrication skills have an increasing competitive edge over conventional builders.

Following this logic to its ultimate conclusion, a greater percentage of work completed in the plant equals greater savings. Since the transportation and hoisting costs for a complete unit are about the same as for the bare frame, a module should have the greatest possible amount of labor and materials embedded before it leaves the plant.

For this reason I can’t agree with the suggestion that the B2 modules are “too complete.” If there are problems with the fit of the façade panels, it is likely because of accumulating tolerances, rather than excessive “completeness.” So the goal was noble, the execution lacking. In fact stacking factory-built volumetric modules provides builders with a golden opportunity to produce precise building geometry in a plant and then export that geometry to the site. Far easier than shipping random geometry to a site, then trying to survey the variations and knock the building into line before tacking on more bits.

On the topic of plant organization, moving boxes down a line is not inherently better or worse than moving workers among the boxes. Assembly lines are expensive to set up and they don’t work well if the product is diverse. B2 modules vary from small triangles with no mechanical-electrical-plumbing systems and lots of facade, to large modules with kitchens and bathrooms. So having all the module types go down the same line would make it difficult to equalize dwell times at each station, not to mention the issues with just-in-time feeding of such a wide array of variants.

On the other hand, a plant making hundreds of nearly identical labor camp modules is well suited to an assembly-line approach. A month ago, I toured a three-tiered modular plant where workers fabricated walls on a loft, then fed them to the assembly line like slices of bread going into a toaster. Meanwhile other workers simultaneously completed underfloor assembly from a pit in the plant floor. A week ago, I was in a plant that shipped 16-ft-wide modules on custom trailers to local building sites. In other words, the correct approach to plant design is to match the factory building, the product and the process.

By including such a wide range of experiences, the article touches on a topic dear to our hearts, which is standardization. With the goal of eliminating the expensive and neverending cycle of invention, experimentation and disappointment, we have been working for two years to develop a flexible yet standardized approach to modular construction. The product we developed is called Vectorbloc. We welcome the opinions of ENR readers and invite anyone with questions to get in touch.

Julian Bowron
Vector Praxis

Sobering History

Just read your very comprehensive articles on modular construction. I thought the details and comments that you received from your interviews were to the point.

The fact that few interviewed totally agreed with the benefits of prefabrication confirms my experience when I, as an engineer, produced concrete modules for housing in New York City, in the 1970s. I worked with Kathy Wilde of the New York City Housing Partnership. We produced thin shell concrete boxes which created 12- ft-wide by 40-ft-long boxes. All the production was done in our own factory in Kearney, N.J.

The dream of modules and prefabrication was originally brought to the building industry by then Secretary of Housing and Urban Development George Romney. Mr. Romney, as a former governor of Michigan, saw the benefits of assembly-line construction of the automobile.

In 1969, he initiated Operation Breakthrough—intended to increase the amount of affordable housing through factory modular construction techniques. Some 20 finalists in Operation Breakthrough were encouraged to complete their systems. None of the 20 systems are in existence today.

I was honored to meet a number of pioneers in the business. The common factor amongst all of us was that we all thought modular housing was the wave of the future and with very few exceptions these manufacturers spent their own money on this concept.

As an engineer I immersed myself in every aspect of the process and would like to share some of my observations. The value of modular is that one systematizes each of the subsystems such as plumbing stacks and heating systems—making these subsystems easy to place into the generic boxes.

The time and motion study clearly shows that repetition of process does increase efficiency. Owning a plant and not having a steady source of market is a great detriment to production. Waiting for orders can eat you up with plant and staff inefficiencies.  The builder frequently gets the benefit of the manufacturer building the module while site and foundations are in place. Last but not least, one must have a module which when stacked must have an exterior structure to avoid the modules having to support the ones above. We did have a HUD approval for a system which used the concrete boxes as in-situ forms.

A final but important fact we discovered was that the module must be 80% complete for its cost to be sustainable.

Vincent DeSimone
DeSimone Consulting Engineers
New York City

Off-site Done Right

I recently read your article "The Promise and Pitfalls of Modular Buildings" and was pleased to see that while many of the concerns around modular construction were touched on, there were a few examples of “off-site construction done right” included as related articles on your site.  I would like to offer another example of “off-site construction done right.”

I believe that it’s safe to say that modular construction will become more and more commonplace for all of the reasons mentioned in your article as well as due to the growing deficit of skilled workers who are able to construct a quality building in the United States. I am fortunate in that I work with a few true visionaries who see this trend becoming something closer to the norm and who took it upon themselves to figure out how to get it right by forming a group called StoPanel Technology.

StoPanel Technology is comprised of a group of contractors from around the country who have come together as affiliates under a single banner to offer factory-constructed building exteriors. These contractors all use a common set of details and specifications to construct a variety of wall systems.

Because they all use the same materials and follow the same guidelines for construction, they are able to share best practices with each other and take advantage of the different areas of expertise that each affiliate brings to the table. Some of these affiliates have been constructing off-site building exteriors for decades while some are brand new to any type of off-site construction.

The combined wealth of knowledge and the shared resources amongst the group are what allows each affiliate to avoid the exact pitfalls pointed out in your article.  The combination of highly skilled contractors and years of experience with off-site construction has already helped StoPanel Technology realize some amazing projects that boast fast, green, safe and cost-effective construction. 

Knowing that modular construction is only going to continue to grow, I would point to StoPanel Technology as a group that is leading by example.  I have to believe that there are other like-minded individuals out there and I would love to hear more of their stories in the future.

John Chamberlin
Product Manager
Sto Corp.

Well Researched

Thank you for a very well researched and informative article about the current state of modular construction and the status of the B2 project.  We as an Industry appreciate your efforts.

Tom O'Hara
Vice President for Business Development
Capsys Corp.
Brooklyn, N.Y.