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 a best option for you next office, classroom or custom building project.
Modular Building Process – Construction Within the Factory
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, often with the use of a lightweight overhead crane, 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, 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.
Modular Construction: On-Site
The main advantage of modular construction is the overlap of off-site building and on-site preparation and the time savings that come with simultaneous progress. We’ve taken you step-by-step through the construction of the individual modules. But what’s happening on-site during a modular construction project?
Permanent Modular Construction On-Site Development
While individual modules are coming together off-site, there is a lot happening at the final build site. This includes:
• Site drainage
• Foundation construction
• Utility installation
Using traditional construction methods, all the above steps would need to be completed in full before building construction could begin. This adds significant time to your overall project timeline and delays your ability to take occupancy of your building.
Foundations for Permanent Modular Construction
There are two foundation types that are primarily used for modular construction projects: on grade foundations and raised foundations.
An on-grade foundation is most commonly used in permanent modular construction installations. It’s created by pouring a foundation wall around the entire building perimeter. Similar to a home foundation, it creates a basement for the building. Using an on-grade foundation requires the individual modules to be set with a crane during final assembly.
The second foundation type, a raised foundation, can be used for temporary or permanent modular construction. Using a raised foundation, modules are placed on concrete piers or blocks. A blocking points plan suggests where to place piers and how much building load each will support. It’s especially useful for temporary modular building because the structure can be removed easily and with less disturbance to the surrounding site. A raised foundation allows the completed modules to be set in place without the use of a crane.
Modular Building Installation & Assembly
Once all on-site preparation is complete, building installation can occur. At this time, the modules are delivered and staged in a specific order to make final assembly run smoothly and efficiently.
Using a crane, the individual modules are placed on the prepared foundation. The modules are precisely designed to match up exactly as they are placed side by side, end to end or stacked based on the final project design.
Once the modular pieces are placed onto the foundation, the individual building components are seamed together. At this point, utility connections are made, interior finishes (ceiling, flooring, and trim work), and exterior additions (decks, ramps, and stairs) are completed.
Here is a quick-motion video of a modular administrative building being assembled on-site. Each modular building component was set in place by crane. The assembly of this two-story permanent building was crane set in six hours.
Compared to traditional construction, the overlapping on-site and off-site progress of modular construction can reduce your time to occupancy by up to 50%.
Do you have additional questions about the modular building manufacturing process? Ask us in the comments!