Sean Studzinski: The Five Key Differences in Prefabricated Modular Methods

by Katie Sloan

In this time of uncertainty and with the current challenges of cost, schedules and labor in the construction industry, we have seen a large resurgence in prefabrication and modular solutions. While these alternative building solutions are a positive for the construction industry, this flood of new offerings into the market has created confusion among those seeking to understand the benefits of this method of design and construction.

In my 24-year career, I have seen a substantial growth in the number of new ‘modular’ companies moving into the prefabrication method of delivery. However, not all prefabrication solutions are created equal. Anyone looking into prefabricated modular solutions should know the two common modular methods: Prefabricated Modular Manufacturing (PMM) and Prefabricated Offsite Construction (POC) and the five key differences between them. 

What is Prefabricated Modular Manufacturing?

PMM is a construction method in which a company has built a manufacturing plant, with company-employed and trained construction workers. The company is licensed and certified by the state for the purpose of manufacturing building portions or modules in an assembly line method to then be transported to and installed or erected at the construction site to achieve a faster construction rate than would traditionally allow if done in an on-site sequential order.

What is Prefabricated Offsite Construction? 

POC is a construction method in which a construction group — typically a general contractor, construction manager or a sub-contractor — is contracted for an individual project, utilizing a temporary facility, warehouse or other large space to construct building portions or modules away from the construction site to then be transported to and installed or erected at the construction site to achieve a faster construction rate than would traditionally allow if done on-site in a sequential order.

Five key milestones and how each method can differ:


The architecture and engineering (A/E) team must be fully on board with the chosen prefabricated solution from the start, whether PMM or POC. The earlier the PMM company is engaged in the design process the better. The PMM team can help to guide the design process for best practices in manufacturing. We call this process DfMA (Design for Manufacturing and Assembly) and one step further, unique to MD+, DfMI (Design for Manufacturing and Installation). These processes assist the A/E team in understanding the logistics of the assembly process, the shipping restrictions and ultimately the installation of the units on-site. With a clear understanding of these elements early in the design phase, the team is less likely to encounter late changes or construction coordination issues. 

The difference in the POC method design process is that the chosen general contractor or construction manager is likely using traditional on-site sub-contractors that do not have experience in prefabrication. This leaves a gap in best practices for prefabrication, as they will provide what they know, which is traditional on-site construction means and methods, fabricated in a rented warehouse offsite. 


The certification and inspection process in the POC and PMM methods are one of the key differences between the two methods. PMM companies are a state certified manufacturer of product. The process in which the manufacturer receives certification from the state to hold a license to manufacture an industrialized modular product is extensive. After plant certification by the state, a third-party inspector checks the product during fabrication and upon completion of the assembly line at the plant. This is how a modular unit can be completely finished out, sealed and not required to be opened until the building nears completion on site.

The POC process is similar to on-site construction inspections, only conducted offsite in a rented warehouse. The general contractor or construction manager is not a licensed manufacturer and must rely on the local Authority Having Jurisdiction (AHJ) to provide the inspections in the same way that they would on-site. This leaves the project dependent on the AHJ’s schedule and availability, often slowing down the process leading to schedule delays or coordination issues.


Commonly overlooked is the current deprivation of skilled labor in the construction sector. Studies have shown a two-to-one margin of skilled labor leaving the market versus those that are coming in among the younger generations. The average age of skilled labor today is around 42.5 with a three-to-one ratio of those over the age of 55 to those aged between 16 to 24. Studies predict over 50 percent of our skilled labor sector will retire over the next ten years with no replacement. The result is substantial cost increases or lower quality construction.

Utilizing the PMM method requires approximately one-10th of the skilled labor required for traditional on-site construction, significantly offsetting deprivation while providing a higher-quality product. The reduction is in the assembly line process — one worker is trained in a multitude of fundamental tasks, which are performed at a higher level without requiring the high-level certifications typical of on-site skilled labor. 

Utilizing the POC method also benefits from smaller work areas and greater supervision, however, it requires a larger number of certified supervisors than PMM. That is because the facility is temporary and not set up in an assembly line process. The supervisor from each sub-trade will be required to cover the entire floor in order to oversee their specific trade in each unit. 

Quality Assurance Versus Quality Control

Quality assurance (QA) versus quality control (QC) are the most substantial differences between PMM and POC methods of delivery. The PMM process begins with QC certification of the manufacturing plant. This is an extensive process regulated by each state and ensures that products being manufactured meet strict guidelines that are applicable nationally, no matter the scale.

The POC build process is similar to traditional on-site construction where contracted sub-trades provide the build. The sub-trades are coordinated across a number of units across a warehouse floor, determined by the size of the space available, with no assembly line process. The labor force is larger than that required with the PMM process, as multiple units are produced simultaneously to meet delivery schedules and on-site erection. These issues, if not properly planned, cause difficulty and delay in coordination and installation, leading to costly change orders.


Safety is the most critical yet most often overlooked factor in deciding upon a method of delivery for a project. Both POC and PMM provide a safer environment compared to on-site construction because both methods are completed in a controlled environment on the ground level.

The PMM method provides a safer working environment because it is built from a regulated QC process. These state regulations provide greater restrictions and requirements for OSHA safety managers and management staff. In addition, the assembly line process, safety protocols and the person managing each station are trained in that specific zone. Much like your everyday home, you know the layout —where fire exits, stairs, extinguishers and fire alarm pulls are located.

The POC method is completed inside a make-shift warehouse for a one-off project, therefore many items are temporary, such as safety equipment and supplies, much like on-site construction. This make-shift environment can create disorientation as the contracted worker will likely be in a different area each day, needing to familiarize the location of safety equipment, safety exits and medical stations daily.

Sean Studzinski is president of ModularDesign+ 

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