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Prefabricated buildings, or prefabs, are buildings with components (walls, roof, and floor) that are manufactured in a factory or manufacturing plant. These components can be fully or partially assembled in a factory, then transferred to the site. This method of building construction is preferred due to its cost efficiency, fast turnaround, and reusability. Common applications of prefabricated buildings are temporary construction facilities, office spaces, medical camps, evacuation centers, schools, apartment blocks, and single-detached houses.
Prefabrication is more efficient than conventional on-site construction since manufacturing through a production line is more controlled. Because most buildings have repeating sections of walls, roofs, and floors, a manufacturing process can be developed by putting together a sequence of operations. These operations can be studied and improved, making the manufacturing process more efficient.
Several precorded prefabricated buildings constructed throughout history can be traced back to nomadic times when people were migrating to discover new lands. Colonization brought the need for transportable houses and camps. However, the need for prefabricated buildings was less urgent back then since once the colony was settled, there was no need for further development.
The method was only extensively developed starting in the 20th century. During the first and second world wars, available labor for construction was reduced since men were needed mostly for the manufacture of war goods. This led to housing shortages that endured until the postwar era. Alternative methods of housing construction were considered to meet the demand.
Although prefabricated structures are produced from modules, they are required to follow the same building codes as permanent structures. Building codes are difficult to adhere to because they vary from state to state or county to county. This aspect of construction is a challenge for permanent and prefabricated building producers. In the United States, modular or prefabricated buildings must meet the International Building Code, which is constantly updated and edited to meet new developments but varies between states.
Before the installation of a prefabricated building, the site for its construction is inspected regarding the type of soil required for the foundation of the structure. For further approval, the site is inspected by a third party to ensure it meets the local, state, and international building codes. Once the various inspections are completed, modular companies must obtain building permits, utility permits, and occupancy permits.
Due to developments and standardization of construction and building codes, coupled with the growing need for housing and office spaces, prefabricated buildings are being innovated continuously in place of conventional construction. The emergence of modeling tools and processes such as BIM (Building Information Modeling) helps architects, engineers, and contractors by digitally representing the characteristics of the structure. BIM enables effective management of the assembly on-site, reducing business risks associated with prefabricated construction.
Prefabricated buildings provide plenty of benefits for manufacturers, contractors, and end-users. The idea of dividing activities on- and off-site enables greater flexibility on the project schedule and costs, provided that the planners have effective project management capabilities. Off-site fabrication also brings the advantages seen in optimized assembly lines. With regards to market opportunities, prefabricated buildings will ride the trend of eco-friendly or green sustainability. Market share of the industry, both residential and non-residential, is expected to rise in the following years.
One of the main benefits of manufacturing through a production line is a faster turnaround. Workers perform their respective tasks repetitively with defined operational sequences, making their actions more efficient than workers on a conventional construction site. Some of the operations can be automated as well. With regards to project planning, prefabricated construction is faster since some of the activities can be done simultaneously. Take site clearing and foundation construction, for example. Actual construction of walls, roof, floors, and even finishing does not start until the site is cleared and the foundation fully cured. With prefabrication methods, a building can be delivered to a site as much as 90% complete. This means a complete facility can be occupied in a matter of days or weeks from delivery.
Weather is a major factor in the construction industry since it cannot be controlled or manipulated. It slows down projects, delays completion dates, and generally disrupts workflow. Weather is a factor that all companies have to account for when planning a project.
Unlike permanent construction projects, weather has little effect on the assembly of prefabricated buildings since 90% of the process is completed in controlled conditions. Prefabricated buildings are built "off-site" in a controlled plant environment, which allows for the construction of new facilities in any weather conditions. Site construction and "off-site" construction are melded together to be able to complete a project during adverse weather or emergency replacement situations where conventional construction methods could not possibly occur.
With prefabrication, these external factors can be minimized. Structural components can be fabricated under more controlled conditions without being affected by the external environment. Shop welding and precast concrete manufacturing are some of the methods that are minimally affected by uncontrolled factors.
Quality control is a major benefit of prefabricated building construction. With conventional site construction, local inspectors will visit the work site at various stages of the process. In the case of the manufacturing of prefabricated buildings, rigorous inspections and scrutiny are required through every aspect of the manufacturing process.
Most prefabricated building manufacturing facilities have quality control inspectors and state and third-party inspectors that approve prefabricated components at every stage of production for strict adherence to drawing and quality control. In a modular plant, key employees and crew foremen have many years of experience and have worked on projects of several types and designs.
Traditional construction and its current workforces consist of unskilled laborers sent to projects by local employment agencies. They are assigned to projects to fulfill labor needs without regard to their skill level. Unlike modular construction with employees with years of experience, construction workers for traditional projects work for companies on a project-by-project basis as temporary or part-time employees.
Quality control is less complicated to implement than on-site construction since the structural components are designed to have repeating features. It is easier to standardize component dimensions and tolerances. Molds, formworks, and temporary fasteners are the same for a typical building component that produces constant dimensions. Also, the quality of a prefabricated building is more likely to be consistent with other prefabricated buildings constructed at different locations, provided that they have the same components. This is because the construction is less affected by local site conditions.
The cost of prefabricated buildings can be comparable to or higher than traditional construction. Its major benefit is in time and efficiency, which are the main reasons for its use. Traditional construction projects can take from six to nine months to complete. Such projects can be completed by prefabrication manufacturers in half the time with the same quality, the results of which are cost savings and immediate implementation of a structure. Each project has components and features that are customized and unique, requiring precision engineering and design, a major advantage of prefabricated buildings.
Some prefabricated buildings are designed to be temporary. These are preferred in applications requiring temporary working spaces for project-based work such as construction jobs, remote healthcare services, research, etc. Prefabricated buildings can be easily disassembled and transferred to different sites. This functionality also results in minimal alteration and preservation of the job site.
This benefit stems from the process‘s efficient raw material utilization and reusability. Conventional construction has more wasted material and temporary components such as formworks, temporary fasteners, jigs, and fixtures, that are discarded after construction. Buildings from on-site construction are mostly permanent. After its intended use, the building will be unoccupied until repurposed or demolished. Prefabricated, modular buildings are easier to repurpose because of their mobility.
Fabrication shops have a more controlled environment than the conditions on-site. Exposure of workers to safety hazards and threats such as working at heights, weather, constrained spaces, and adjacent construction operations are greatly minimized since most of the work is done in fabrication shops. where construction operations can easily be separated and ergonomically designed.
Many factors that determine the lifespan of any building, which include installation, maintenance, and environment. In general, prefabricated buildings have a lifespan of over 30 years and normally outlive their original purpose. The guiding principle regarding prefabricated buildings is their adherence to the same rules of construction that moderate and control traditional construction.
Prefabricated buildings are subjected to the same scrutiny and inspections as traditional structures. The one caveat that differentiates prefabricated buildings from traditional buildings is the constant and continual inspection of components and materials during assembly and manufacturing. This aspect of the prefabrication process makes such buildings more responsive to potential defects, errors, and inferior materials.
In a way, prefabricated construction challenges the existing methods of conventional construction. Prefabricated construction is not always applicable and may cause more drawbacks instead of gaining the expected benefits. Prefabricated construction can be considered as high-risk, high-reward that threatens trust from all stakeholders. Below are some of the risks and challenges associated with prefabricated construction.
The concept of prefabricated buildings is hundreds of years old, stretching back to the 15th century when William the Conqueror invaded England. Over the centuries, prefabricated buildings have been improved, adapted, changed, and altered to fit the needs of society, with prefabricated farm buildings being used during the Gold Rush of 1848, and portable cottages appearing in Great Britain during the same period.
At the beginning of the 20th century, prefabricated home kits were sold by catalog with precast concrete materials available as foundations. The rapid growth of prefabricated buildings began after World War Two, which had brought the introduction of Quonset huts as temporary barracks for soldiers during the war. From the simple design of Quonset huts has developed an ever-growing industry that provides several types of prefab buildings to serve the needs of manufacturers, farmers, and homeowners.
The two main types of prefabrication are volumetric or modular and panelized. Both types are constructed using timber, steel, concrete, and fiberglass, with certain types being a mixture of the various materials.
The various components of prefabricated buildings are engineered at a factory and delivered to a location where they are assembled. Prefabricated buildings are a viable and reliable alternative for creating work space, storage area, and flexible manufacturing facilities. The components of prefabricated buildings include framing, secondary supports, wall and roof panels, door and window frames, fasteners, and sheeting and insulation.
Although the larger components may seem to be the foundational and necessary parts of the assembly of prefabricated buildings, the most essential and crucial items are the screws, bolts, nails, and fasteners required to hold the various elements together. A wide selection of fasteners is carefully engineered and designed for long use and easy installation.
Components include construction elements such as windows, doors, and trusses, which by themselves are not complete panels. Among the prefabricated materials, these have the least amount of off-site assembly, but usage is more flexible since they can be placed and installed according to actual site conditions.
Prefabricated panels are two-dimensional components that are put together on-site to form a building. They require more on-site work than modular prefabricated buildings. These components are commonly available as sub-assemblies with complete finishing and installed features such as windows, doors, and insulation. Panels can also be supplied as bare structural frameworks in which the additional components can be later added on-site. Different types of prefabricated panels vary according to material and form.
Prefabricated modules are three-dimensional in construction, usually made up of four shop-assembled panels. Several modules are placed adjacent or on top of each other, forming the whole building. Modules are connected by inter-module connections, which are bolted on-site. The term modular buildings are synonymous with prefabricated buildings because it is the most popular among all types. All advantages of a prefabricated building are seen in a modular building. A single module can be the complete building, with minimal site work required. There are different types of modular buildings according to their form of construction.
Hybrid prefab systems utilize both three- and two- dimensional components from modular and panel systems to create a whole or a part of a building. This type can also be referred to as mixed modular and panel systems. Modular units have the advantage when it comes to construction quality and detail but are sometimes limited by assembly and transportation constraints. The three-dimensional modules are used for highly serviced and higher value parts such as kitchens and bathrooms. Panelized components are added to the assembly due to their flat pack or ready-to-assemble construction. Two-dimensional panels are used for floors and walls of more open areas.
These types are stand-alone modules or buildings. Complete buildings are delivered and installed at the site with prepared foundations. Complete buildings require the least amount of site work but are limited by hauling capacity limits and road width and height clearances.
The majority of prefabricated buildings follow an established set of design, engineering, and fabrication processes. In addition to these tried and true methods, certain variations make prefabricated buildings marketable and more attractive. The Quonset hut is one unique design that has been around for many years and is still used as a temporary type of prefabricated building.
Quonset huts can be said to be the original and first prefabricated buildings. Several civilizations used their design over the centuries, and they still find use today. Unfortunately, in many muncipalities, the appearance of QUonset huts has been banned.
Quonset huts are made from steel alloys and are known as arch steel buildings because of their dome shape. Of the many varieties of prefabricated buildings, Quonset huts are affordable, have low maintenance, and can withstand all types of weather conditions and earthquakes. The design of Quonset huts goes back centuries and has been used to provide shelter for several civilizations.
Modern Quonset huts take the advantages and designs of ancient Quonset huts and have added modern engineering techniques and technologies. They are manufactured in two feet wide sections, which can be easily reshaped and designed to meet specific and unique requirements. The basic structure of Quonset huts depends on the arch, which provides structural support and a clear open design without interior supports to get in the way.
The arches of Quonset huts are made of galvanized steel. The various panels are corrugated to enhance and strengthen the arches. This aspect of Quonset huts offers the unique features of surface and structure being the same. The segments and arches are bolted together with the arches anchored to the foundation slab. A base plate connected to the arches, lines up the arches without the need to twist them in place.
Fiberglass is used as a building material for prefabricated buildings due to its lightweight and durability. It is a mold-free and rust-free material that can be used for outdoor structures without being damaged by water or the build-up of moisture due to its tightly sealed structure. In the construction of prefabricated buildings, fiberglass is used for wall cladding material because of its resistance to wind, heat, and cold effects.
The many shapes and designs of fiberglass come in several color options. Its flexible nature makes it resistant to tensile stress because of its plastic composite base material, which contributes to the strength and durability of fiberglass prefabricated buildings and their appearance. Fiberglass material provides exceptional structural integrity and insulation comparable to R-18 and R-24.
Prefabricated buildings can be used as temporary locatable buildings that are used indoors or outdoors. They have a panel-type construction with a frame made of steel or aluminum with a roof. The walls of shelters can be made of several types of materials, including fiberglass, glass, and polyvinyl chloride (PVC). Prefabricated temporary shelters can be installed and set up quickly. They are durable and maintenance-free and are capable of withstanding harsh weather, including radical temperature changes and humidity.
Although prefabricated shelters can be used as huts for the protection of personnel, they are widely used as storage units for rescue equipment, sound dampening for pumps, and protection for sound room equipment. Since they come in several shapes and sizes, prefabricated shelters can be adapted to meet the needs of a wide assortment of applications. They take half the time to assemble and implement, which makes them ideal for use during emergency conditions.
Temporary, relocatable modular buildings can be reused or repurposed many times and be moved to different sites. They are intended to serve as short-term buildings and are designed for easy teardown and relocation. The designation “temporary” refers to how the structures are installed. With proper care, temporary prefabricated buildings can last for 25 to 30 years, after which the components are typically repurposed or recycled.
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