How Are Modular Buildings Built? Learn About the Prefab Building Process

Modular buildings are an economical, safe, and fast alternative to traditional construction, but what is modular building construction and how are they built? Being a modular building dealer, this is one of the most frequently asked questions we get from our clients. Let’s dig into how modular buildings are made and why it may be the best option for your next office, classroom, or custom building project.

In short, the prefab building process is when the individual modules of a building are built in a controlled factory setting using an assembly line process, beginning with building the frame and ending with the interior and exterior finishes. Completed modules are delivered to the site and pieced together to form a finished building. But there’s so much more than that! Here’s an in-depth look at what goes on in the modular building factory and at the final building site.

Step 1: Framing and Floors

Construction starts with the welding of a steel frame to the designated size of each individual module. Typically modules are 14′ width by 76′ length, mainly due to shipping restrictions. While the frame is being welded, the floor joists and decking are being built. Then the floor is installed on the frame as the modular building begins moving down the assembly line.

Step 2: Attaching the Walls (and More!)

The next stop on the assembly line is the walls. They are built using traditional wood studs which are spaced according to wind load requirements. The walls are constructed with the wood lying in a horizontal position then lifted to their vertical position, to be joined with the flooring and frame.

After the walls are secured to the flooring, the designed interior wall finish is installed. At the same time the windows, insulation, electrical wiring, plumbing for the kitchen and bathroom, and any custom components are installed from the outside of the module. While this occurs the roof is being fabricated at the next assembly line station.

Step 3: Installing The Roof

The module moves down the assembly line and the roof structure is ready to be installed. An overhead crane hoists the roof onto the walls, ensuring careful control and safety. With the roof securely fastened, the module is really taking shape and the finishing work can commence.

Step 4: Interior and Exterior Finishes

Final touches are made on the interior walls while the specified flooring and fixtures are installed. On top of the module, duct-work is run, as well as additional electrical wiring and other components as necessary. Exterior finishes are attached while doors and interior trim are completed. Finally, the roof decking is installed and covered with the designated exterior waterproof surface.

In a typical modular construction project, up to 90% of the construction is completed in the off-site process. As each module reaches the end of the assembly line it is weatherproofed with plastic wrap and moved to an outside staging area at the manufacturing facility to await delivery to the site. Modular buildings are fabricated and stored in a predetermined order so that they can be delivered to the project site and installed to maximize schedule efficiency.