The answer may surprise you.
A manufactured home is a single-family house constructed entirely in a controlled factory environment, built to the federal Manufactured Home Construction and Safety Standards – better known as the HUD Code.
Many types of structures are built in the factory and designed for long-term residential use. In the case of manufactured and modular homes, units are built in a factory, transported to the site and installed. In panelized and pre-cut homes, essentially flat subassemblies (factory-built panels or factory-cut building materials) are transported to the site and assembled. The different types of factory-built housing can be summarized as follows:
Manufactured Homes: These are homes built entirely in the factory under a federal building code administered by the U.S. Department of Housing and Urban Development (HUD). The HUD Code went into effect June 15, 1976. Manufactured homes may be single- or multi-section and are transported to the site and installed. The federal standards regulate manufactured housing design and construction, strength and durability, transportability, fire resistance, energy efficiency and quality. The HUD Code also sets performance standards for the heating, plumbing, air conditioning, thermal and electrical systems. It is the only federally-regulated national building code. On-site additions, such as garages, decks and porches, often add to the attractiveness of manufactured homes and must be built to local, state or regional building codes.
Modular Homes: These factory-built homes are built to the state, local or regional code where the home will be located. Modules are transported to the site and installed.
Panelized Homes: These are factory-built homes in which panels -a whole wall with windows, doors, wiring and outside siding – are transported to the site and assembled. The homes must meet state or local building codes where they are sited.
Pre-Cut Homes: This is the name for factory-built housing in which building materials are factory-cut to design specifications, transported to the site and assembled. Pre-cut homes include kit, log and dome homes. These homes must meet local, state or regional building codes.
Mobile Homes: This is the term used for manufactured homes produced prior to June 15, 1976, when the HUD Code went into effect. By 1970, these homes were built to voluntary industry standards that were eventually enforced by 45 of the 48 contiguous states.
Source: Manufactured Housing Institute