Modular construction is a term that is used for the factory production of pre-engineered building units that are delivered to site and assembled as large volumetric components or as substantial elements of a building. The modular units may form complete rooms, parts of rooms, or separate highly services units such as toilets or lifts. Modular units can usually forms a self supporting structure in their own right or, for tall buildings, may rely on an independent structural frame work.

The motivation for using modular construction lies in the business-related benefits that make this form of construction more attractive to the client than alternative forms of conventional site-built construction. In such cases, the design decisions are most strongly influenced by:

• Speed of construction on site. Rapid construction leads to business-related benefits to the client, due to early completion and early return on capital investment.
• Avoidance of disruption and loss of operation of adjacent buildings, such as hotels, and in sensitive sites.
• Buildings or components with a high degree of servicing. These require careful site
  installation, and pre-compliance trials, which are better carried out off site and off the critical construction path.
• A large number of regular or repetitive units. Factory production can facilitate transportation and can achieve economy of scale in production.
• Planning constraints, such as on deliver times, time of working, noise control on site.
• A short “weather window” or other site constraints to the construction operation.
• Lack of suitable skills at site. This might be the case at a remote site.
• Client requirements for an exceptionally high degree of quality control. This can best be achieved by off-site manufacture and pre-installation checks.
• A requirement for a single point procurement route. This can be achieved through a design manufacture and build service, which the modular industry provides.
• Security or other related issues on site. Construction operations can be controlled more precisely when modular units are used.