There is a well worn adage in the housing industry that factory building is simply site building under a roof. The comment has some basis in fact: most homes, regardless of building method, use similar framing techniques and the same materials, and in many instances it is difficult to tell from the finished product if a home was built from thousands of small parts assembled at the building site or was primarily fabricated in a factory and transported to the site as relatively few pre-finished modules.

However, viewed from the perspective of the total process, site building and factory building represent, in many fundamental respects, vastly different methods for providing housing. Most site builders, for example, are land developers and the home is one part of an overall package sold to the buyer. For factory home builders, the home is the product. Site built homes are generally sold by the building company; factory built homes are sold by a builder (modular) or retailer (manufactured), thereby insulating the customer from the company that actually does most of the building. In addition, site built homes are erected mainly at the building site, often by several independent subcontractors, working out in the elements, effectively customizing the home to the site as the work proceeds. Factory builders are product assemblers working with a closely coordinated and integrated team in a controlled and, from a production standpoint, highly controllable environment.