"Modular buildings typically are inspected at the factory by a third-party inspection agency. These independent agencies provide certifications and/or certificates to the local code official when the building is delivered to the site. When this is provided, there is no need for local inspectors to perform 'rough-work' inspections or to look behind finished walls--this has all been done by the third-party inspector who attests to the proper completion of the work. Local inspectors are responsible for inspecting foundations and site work, utility installation and connections, and the final assembly of the structure. Most recognized third-party inspection agencies are certified and recognized by the Federal and State governments to provide in-plant inspection and design approval. Modular buildings may have large concealed void spaces in the walls between modules. There also will be a large interstitial space between each story. In each case, the inspector should verify compliance with the draftstopping and fireblocking requirements in the code."
Coffee Break Training - Fire Protection Series No. 2008-44
United States Fire Administration: http://www.usfa.fema.gov/