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Home inspectors are trained to inspect site-built homes, but are often asked to prepare a report on mobile and modular homes. With today’s modern designs, it is sometimes hard to tell from the street what is site-built, mobile, or modular construction.

To clarify the frequent confusion in these terms, definitions are in order:

  • Mobile Home
  • -- A home that is factory assembled on a metal chassis with axles and is pulled down the highway to the home site, (often two or three units are joined on one site referred to as a double-wide or a triple-wide) -- e.g., what used to be called a Trailer or a Coach.
  • Modular Home
  • -- A home in which major components are constructed in a factory, but are then shipped to the home site for assembly into their final form -- e.g., a pre-cut log home or a panelized exterior wall home.
  • Site-built Home -- A home with components that are shipped to the home site as individual pieces and are cut to fit and assembled on-site -- e.g., the typical American tract house.

    Although home inspectors may inspect mobile homes and modular homes, there are important differences compared to site-built homes.

    Mobile homes are most often placed on sites within a mobile home park. The “coach” sits on a foundation of block piers or steel jacks. The connection to the utilities must all be flexible since the foundation is flexible. In earthquake Zone-1 or hurricane territory, it is critical that these homes be strapped to the earth so they won’t fall off of their piers.

    Other unique mobile home considerations are:

  • Older units, (built before 1975), may have been built without benefit of code-compliance inspections.
  • There is required bonding of all metal parts including the chassis.
  • The primary electrical connection can be, what amounts, to a big drop cord.
  • The need for special gas appliances, (so labeled), for use with mobile homes -- this includes a metal fireplace, (if any).
  • Most coaches have metal roofing and the unusual annual maintenance necessity of sealing around all of the plumbing and exhaust vents through the roof -- (This makes for an interesting difference since freshly caulked plumbing and exhaust vents usually means it was leaking with site-built Homes, but just the opposite with mobile homes).
  • The interior walls are often only two inches thick with surface mounted door hinges.
  • Exterior windows and doors of mobile homes are not flashed in conventional ways, which often results in water stains on the interior window sills.

    Modular homes also have unique features:

  • Much of the “code-compliance inspections” take place at the factory.
  • Often the panels are closed-wall, which means that the wiring for outlets and switches is run through conduit or chases designed into the system. This may mean an extraordinary number of junction boxes visible in the crawl space.
  • Exterior siding can be back-nailed - meaning there are no ugly nail heads on the surface siding like redwood or cedar. This is a particularly appealing concept if the home is to be built near the coast where sea-spray can quickly rust most exposed fasteners.
  • Since roof and floor panels are constructed in the factory, this means that they often are designed to span extraordinary distances that would be forbidden on a site-built home.
  • Because the panelized pieces must fit together, foundation installations of modular homes are usually exacting. It is even quite acceptable in remote locations, (far from a ready-mix plant), to have wood foundations of pressure treated material..

    These differences in mobile and modular home construction and installation techniques means that a home inspector should have special training before taking on the duty of inspecting them. Most home inspectors are not so qualified.

    To my knowledge, the American Institute of Inspectors®1, (a nonprofit trade association of home inspectors), is the only national association that offers Certification in Mobile Home Inspections to its members. Local inspectors with this skill can be located at the association’s web site: www.inspection.org.

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