Prefab building or modular construction refers to a method of building a structure, rather than a description of the finished product. Prefab buildings are typically built 60 to 90 percent "off-site" in a three-dimensional form, designed to be constructed at one location, and then used by occupants at another.
Modern, custom, multi-story, factory-built buildings with concrete and steel floors, brick exteriors, sheet-rock interiors, windows, lighting, computer hook-ups, electrical service, plumbing, heating, air conditioning and restrooms can include everything you need and often are constructed in half the time of a site-built building.
While modules are being constructed in a factory, site work is occurring at the same time or in some cases prior to construction. This allows for much earlier building occupancy and contributes to a much shorter overall construction period - reducing labor, financing and supervision costs.
Also unique to prefab building is the ability to simultaneously construct a building's floors, walls, ceilings, rafters and roofs. During site-built construction, walls cannot be set until floors are in position, and ceilings and rafters cannot be added until walls are erected. On the other hand, with modern modular methods of construction, walls, floors, ceilings and rafters are all built at the same time, and then brought together in the same factory to form a building. This process often allows modular construction times half of that of conventional, stick-built construction.
Traditional building techniques, quality manufacturing and third-party administered random inspections - combined with testing and certification services for quality control - assure that permanent modular buildings are built in strict accordance with appropriate local, state, and national regulations and codes. Some would even say that due to the extra durability needed for travel, factory-built buildings are built better than conventional structures. As a result of meeting and often exceeding site-built standards, modular construction has the same life expectancy as traditionally built buildings, and can, with proper maintenance, last indefinitely.