Modular construction (also referred to as off-site and/or volumetric construction) is growing in popularity because it offers several advantages over traditional construction. Chiefly, these advantages include:
- Shorter construction times (leading to a quicker ROI for owners), and
- Cost certainty (obtained through fewer mid-project changes and weather delays, and, to a lesser degree, fewer on-site injuries)
These advantages are obtained through a carefully planned design and construction process. Unlike many traditional construction projects, modular construction leverages a precise timetable and a predictable, industrialized assembly process to realize its value.
In this article, each step of the modular construction process will be explored and reasons for these advantages will be detailed.
Step 1: Design approval by the regulating authorities and end users
In the modular building process, the project begins at the design phase. Architects and engineers, using building information modeling (BIM) systems and other software, create exterior and interior plans. Once plans are approved by the owner, they are submitted to the locality or third-party service for approval and building permit applications are submitted. The manufacturing of components begins once the design is finalized.
Note: Modular buildings must follow the local building codes and zoning regulations. The modular building contractor should already know the regulations that apply to the project based on the address of the physical building site and the agencies that have jurisdiction over that area.
Step 2: Construction of modular components in a controlled atmosphere)
The module components are built in a controlled offsite factory environment while site excavation and grading is going on at the same time. The amount of work (60% - 90%) performed in the factory can vary based on owner requirements. For example, it can include assembling basic structural components (like exterior and interior walls, flooring, and windows), installing mechanical, plumbing, and electrical components, and completing interior finishes such as drywall and cabinets. Because so much can be accomplished off-site, the labor force in the factory can consist of any or all of the following:
Inspections by a third party or other building code official takes place at various stages in the factory. Upon completion of the modules, they are prepared for transportation.
Step 3: Transportation of modules to a desired location
Modular buildings are shipped on chassis integrated into the structure or carriers towed by trucks. Due to the need to transport the modules to the final site, each module must be built to independently withstand travel and installation requirements (e.g., high winds, manipulation by cranes). Of note, the resiliency of the individual modules contributes to the greater structural strength of the final building, another advantage of modular construction.
Transportation of the modules depends upon some important factors such as the cost and method of transport, travel distance, and weight. It usually isn’t feasible to ship modules far due to road size and load restrictions. Generally, the maximum desirable distance for transportation of modules is 250 to 400 miles. The costs and transportation difficulties greatly increase for building sites farther than 400 miles.
The maximum width, height, and length of individual modules that can be transported is dependent on several criteria including local Department of Transportation restrictions; bridges, overpasses, utility lines that cross over roadways; and the actual route itself from the factory to the final destination. For ease of transportation, modules commonly have measurements of 15-feet wide, 12-feet high and 60-feet long, although these measurements can differ greatly in any direction based on a number of factors.
Step 4: Erection of modules to form a finished building
Once at the jobsite, the modules are stacked by crane or rolled onto the foundation, bolted together and sealed for weather-proofing. The modules are then connected together, utilities are hooked-up, exterior siding and roofing components are completed, and site work is finished. The final construction stage includes completing exterior systems such as cladding, final caulking and sealing, adding stairs and elevators, and competing any interior elements such as painting, trim, cabinets, countertops, and installation of appliances that didn’t occur in the factory.
Modular construction offers an accelerated schedule for designers and builders and an accelerated ROI for owners. This is primarily accomplished by working on multiple fronts simultaneously. While modules are built and furnished in a controlled offsite location, site work can occur at the same time, eliminating the need for less efficient, strictly linear process.
As illustrated in Figure 6, parallel construction work can be performed in the modular construction process. This modular process allows reduced construction times of about 30% - 50% that of conventional construction.
The process of modular construction is strict. Plans must be finalized early and stakeholders must have a complete understanding of the entire building process, but the advantages of modular construction are indisputable. To find a modular builder near you, click here.
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