Modular homes and trailer houses (also called 'Manufactured Housing') are often put in the same category in people’s minds. They are completely different. Modular Homes are very similar to traditionally constructed homes, only they are built in a factory and delivered to the job site in large modules. They are built to the same building codes as site-built homes and are thoroughly inspected during construction by the factory's quality assurance inspectors as well as a third-party agency to ensure complete code compliance. They then have the required labels affixed to each home to prove code compliance. All modular homes must be placed on permanent foundations.
In contrast, trailer houses (HUD code homes) are built on a trailer frames with axles under them. They are typically placed on concrete slabs and blocked up with dry stacked concrete blocks. They are built to a federal code which allows them to build them much cheaper and lighter-duty than local building codes allow. Because of this, trailer houses lose value quickly. These facts have rightfully given many people a low-class impression of trailer houses, and they are not permitted in some municipalities.