The USFA/ National Fire Academy published an excellent series of informational fact sheets on Factory Built Modular Construction. The six part series included a wide varity of general information for the fire service. The series included;

Part I: Factory-Built Structures
Part II: Modular Construction
Part III: Recognizing Modular Construction
Part IV: Fire Response to Modular Construction
Part V: Factory-Built Construction Codes
Part VI: Inspecting Modular Construction

Most of us are familiar with site-built, or “stick-built” construction. These terms are used to describe the traditional method of constructing a building, where individual pieces of lumber or other materials are delivered to the site and are assembled in a logical sequence. Increasingly, buildings are being assembled in a factory and delivered to the site in one or more pieces for final assembly. Once a building is completed, very few people can tell the difference between buildings built using the different construction methods.

There are several different kinds of “factory-built” homes, the first three of which must meet State or local building codes:

Modular Buildings: These are built in a factory in different sections or modules. The modules are transported to the site, installed on foundations, and bolted together.
Panelized Buildings: These are buildings in which panels—a whole wall with windows, doors, wiring, and outside siding—are transported to the site and assembled. They may be constructed of standard wood framing, concrete, or structural insulated panels (SIPs).
Precut Buildings: This describes structures where building materials are factory-cut to design specifications, transported to the site, and assembled. Precut buildings include kit, log, and concrete buildings.

Manufactured Buildings: These buildings may be single- or multisection and are transported to the site and installed. Part of the definition of a manufactured home requires that the home sections be built on a permanent chassis. The home does not require a permanent foundation, although they are being installed on such in many areas. The definition excludes recreational vehicles.” Manufactured homes must comply with Code of Federal Regulations, Title 24 (CFR 24), Part 3280—Manufactured Home Construction and Safety Standards, which supersedes local codes. It is important to note that, while manufactured homes are not required to conform to local building codes, their installation may be governed by local zoning laws.

http://www.usfa.dhs.gov/nfa/coffee-break/index.shtm
http://www.usfa.dhs.gov/downloads/pdf/coffee-break/cb_2008_39.pdf
http://www.usfa.dhs.gov/downloads/pdf/coffee-break/cb_2008_40.pdf
http://www.usfa.dhs.gov/downloads/pdf/coffee-break/cb_2008_41.pdf
http://www.usfa.dhs.gov/downloads/pdf/coffee-break/cb_2008_42.pdf
http://www.usfa.dhs.gov/downloads/pdf/coffee-break/cb_2008_43.pdf
http://www.usfa.dhs.gov/downloads/pdf/coffee-break/cb_2008_44.pdf