Prefabrication vs. Modular Construction: Differences, Benefits & Drawbacks

The terms “prefabrication” and “modular construction” tend to be used as stand-ins for one another. However, while they describe similar concepts, they are subtly different in meaning. If you work in or around the construction industry, you should understand the distinction.

What Is Prefabrication?

Prefabricated construction, or prefabrication (prefab), is a building construction process that utilizes offsite manufacturing capabilities for building components or systems. While atomized building components like floor tiles, roof shingles, and wall studs are almost always manufactured in offsite factories, prefabrication refers to offsite finishing (or partial finishing) of structural systems, mechanical systems, or entire rooms.

What Is Modular Construction?

Prefabricated construction often involves modularity, where building systems or components are built offsite in standardized, modular fashion. Individual modules may be as simple as a piece of a building facade or as apparently complex as a finished bathroom. Regardless of size or complexity, building modules are built in a climate-controlled facility and then assembled with other modules at the construction site.

Benefits of Prefabrication and Modular Construction

Prefabrication and modular construction might have slightly different meanings, but they share the same general benefits.

• Good for tight or hard-to-reach sites. Prefab or modular construction makes sense for construction sites where access is a barrier to efficient work. Here, “access” can mean tight exposures (e.g., in a densely built urban environment) or remote geography (e.g., in a rural area with limited local labor and/or poor road systems).
• Faster construction timelines. Prefab and modular builds generally take less time to complete than traditional builds because offsite production can occur simultaneously with onsite finishing. This is an advantage for projects in areas with short construction seasons or on sites with high carrying costs.
• Potential for higher construction quality. Because prefabrication occurs in climate-controlled facilities with high-precision equipment, it’s considered higher quality than traditional construction, as long as onsite finishing is done properly.
• Potential for less construction waste with lower embodied carbon. Prefab and modular construction is less wasteful than traditional construction. This reduces losses for developers and their contractors while trimming finished systems’ embodied carbon.

Drawbacks of Prefabrication and Modular Construction

Prefabricated and modular construction techniques don’t make sense for every project. These are their four biggest drawbacks.

• “Take it or leave it” design. Prefab and modular designs are customizable, but only up to the point of fabrication. After that, by definition, they are not. This is not always a disadvantage, but it certainly can be in the face of last-minute building design changes or unexpected onsite conditions.
• Limited room for modifications after the fact. The “take it or leave it” aspect of prefab and modular construction leaves less room for modification after occupancy. It’s possible to renovate or retrofit modular buildings and/or prefabricated components, but the process may be more expensive or time-consuming.
• Potential for overengineering. Modular buildings, in particular, run the risk of overengineering. This is less of a drawback from a construction quality perspective than it is from a cost-of-construction perspective. End-users need to think carefully about what they need from their buildings, then design accordingly.
• May not be cost-effective in some locations. Prefabricated and modular construction makes the most sense in areas with robust prefab supply chains, and particularly in relatively close proximity to modular construction facilities. This will be less and less problematic if (as anticipated) modular construction becomes commonplace, but it remains an issue in many places for now.

End-users and contractors curious about prefabricated and modular construction should understand that these techniques are useful. They are even, at times, superior to traditional construction. Their results will likely improve over time. But, at least for now, they are not miraculous and certainly not foolproof.