Prefabrication is nothing new to the construction industry.  And, over the past several years, we have seen a rather significant increase in the utilization of prefabrication.  With this increase, however, it has revealed some vulnerabilities that, if not properly managed, lead to undesirable results.  Let us take a closer look…

Prefabrication is the assembly of buildings or their components at a location other than the building site.  Some contributing factors that have gained favorable recognition of prefabrication in construction projects stem from factors such as Covid, market variability, and labor shortages. The key benefits of assembling various building components in a factory-like setting include:

• Improved quality and consistency
• Improved labor efficiency and production
• Improved schedule flexibility and enhancements
• Reduced material waste and lost time incidents
• Reduced on-site installation labor
• Favorable cost benefits and effectiveness

For these many reasons, the construction industry is finding more and more ways to embrace prefabrication as a normal practice and apply it more broadly across the various building systems. So, the focus we look to elaborate on is managing the process and having the necessary and applicable controls in place to execute the work.

The process, or also commonly referred to as the method, of prefabrication drives early coordination into projects. This naturally creates a conduit for increased communication in preplanning efforts and promotes early engagement amongst the team. As we are all aware, project success starts day one; so, having a process, or method, in place that recognizes the value of early communication is a significant benefit to steering a project towards success. But let us dive a bit into implementation.  

In numerous instances, we are finding a vital step in the preplanning effort may not be in full consideration at the very early stages of a project. Utilizing prefabrication in a broad sense may be lacking consideration of governance and control of the prefabricated system itself. Many projects rely on building component specific project specifications and design, such as manufacturer data, performance criteria, tolerance, execution, etc. But assembly of multiple building components before reaching the building site has added layers of consideration that may not be completely apparent until the system is being installed. Of considerable concern, in many cases, is cumulative tolerance.

Cumulative tolerance, also known as tolerance stack-up, is the effect of all individual building component tolerances as part of a system or assembly. In traditional design and construction of various building systems, manufacturer tolerances and field installation tolerances are generally accounted for and occur component by component.  This provides flexibility for aesthetics, such as lining up vertical and horizontal joints, while constructing a system that functionally performs. Introducing prefabrication into a design that relies on these numerous component-by-component tolerances can create significant issues.

For instance, five curtainwall units installed in the field have six total joints with plus/minus tolerance flexibility.  Those same five curtainwall units prefabricated as one five-unit segment now have four joints assembled in a factory that can maintain zero tolerance and leaves two joints in the field to potentially account for the cumulative tolerance of the components making up that portion of the system. This, in turn, leads to oversized and/or inconsistent field joints and the potential of performance issues at concentrated locations.

Establishing governance and control for the prefabricated system itself needs to be identified early in the process by working collectively with all members of the project team, including owners, designers, contractors and manufacturers.  Consideration of items such as manufacturing parameters of individual components, prefabrication assembly requirements, onsite preparation, sequence of installation and execution, local building code requirements, performance functionality, and aesthetics, is critical.  The unique perspectives of each team member and evaluation of individual components making up a prefabricated system will help to establish a clear set of boundaries to achieve a seamless final installation. 

So, as we continue to recognize the many advantages of prefabrication and its broadening role in the construction industry, it is imperative to manage the process and have the necessary and applicable controls in place to execute the work.  With implementation of a collaborative approach and early recognition of the importance of managing the prefabrication process, issues such as cumulative tolerance can be vetted to minimize and avoid undesirable results.