How Prefab Houses Work

Prefab House Construction

Workers cover the walls of a FEMA manufactured home in 2005.
Workers cover the walls of a FEMA manufactured home in 2005.
David McNew/Getty Images

Prefab houses are constructed from the inside out. They are manufactured in the following order in a couple of days or less, with inspections following each step (the process can take longer if the buyer has customized the home):

  1. The floors are assembled first. There is usually a wood frame under the floor for attachment of wall panels.
  2. Wall panels are attached next with bolts and nails. Panels are insulated and windows cut out before the panels are attached.
  3. Once the house structure is in place, the plumbing, electrical wiring and drywall (including the ceiling) are installed.
  4. The roof, typically constructed in another part of the factory, is set on top of the walls. In some prefabs, workers attach the roof on-site after the rest of the house is constructed.
  5. Exterior and interior finishes are added, including siding, cabinets, vanities and backsplashes. The walls are also painted.

Once the housing units are constructed, they need to get to the owner's land. The transportation of the modules is limited by roadways, overhangs and power lines. The builders have to scout out all these factors before delivery, but in general each unit must be less than 16 feet wide, 60 feet long and 11 feet high. Because travel can be unpredictable, buyers are usually on site with independent contractors to inspect the units for scrapes and cracks.

The house has to have someplace to sit, so a foundation is required. Before the home arrives, homeowners must have the land excavated and have a foundation in place. The foundation can be poured concrete, concrete blocks, basements or crawl spaces.

The house arrives and is placed by crane on the foundation. Workers use heavy-duty cables to move the units, which come together at points called marriage walls. The marriage walls tie the house together and ensure that it is level and properly bolted together. At this point, the roof is placed if it was not factory-installed. A hinged roof, also made in the factory, is unfolded onto the house. The entire delivery and placement of the house can usually be completed in about a day. After that, decks, staircases and extras can be installed.

Variables such as customization, financing and factory schedules can contribute to the process, but from choosing the house to completion, most manufacturers give a timeframe of a few months. ­

On the next page we'll learn about prefab-home trends in the United States and around the world.