Modular home

Key Takeaways

• A modular home is built in large factory made sections, trucked to the lot, and joined together on a permanent foundation.
• Washington statutes call the category factory built housing. RCW 43.22.450 defines it as a structure designed primarily for human occupancy, other than a manufactured or mobile home, that is entirely or substantially prefabricated away from the building site.
• Factory built housing in Washington is built to the State Building Code, chapter 19.27 RCW, the same code a site-built house must meet, while a manufactured home is built to the federal standard adopted under the national manufactured housing construction and safety standards act of 1974.
• The Department of Labor and Industries approves the plans, inspects the units, and attaches the insignia that lets a factory built house be sited in Washington.

What It Means

A modular home is a house built in large sections, called modules, inside a factory, then trucked to the lot and joined together on a permanent foundation. Prefabrication is the whole point. Framing, wiring, plumbing, insulation, drywall, and often the cabinets and fixtures go in indoors on a production line, where weather never stops the work and inspection happens at the same station every time. What comes off the truck is far more complete than panel construction, which delivers flat wall sections that still have to be stood up and finished on site.

The distinction worth holding is the code the house is built to. A modular home is built to the same building code as a house framed on the lot, so once it is set, tied together, and connected, it is an ordinary improvement to the land. A manufactured home is built instead to a federal construction standard, on a permanent chassis. That single difference drives most of what follows: how the home is inspected, how a lender underwrites it, and which comparables an Appraisal pulls to value it.

How It Works in Washington

Washington does not use the word modular in its statutes. The category is factory built housing, defined in RCW 43.22.450 as any structure designed primarily for human occupancy other than a manufactured or mobile home, the structure or any room of which is either entirely or substantially prefabricated or assembled at a place other than a building site. The Department of Labor and Industries runs the program, approves the design plans, and inspects the units.

The code that applies is the State Building Code, chapter 19.27 RCW, together with the energy standards in chapter 19.27A RCW and the electrical rules in chapter 19.28 RCW. WAC 296-150F-0600 says so directly, and it is the reason a modular home in Washington sits on the same code footing as a site-built house and becomes ordinary Real Property once it is affixed. Before a unit may be sited here it needs a state insignia: WAC 296-150F-0200 requires an insignia for each factory built house, commercial structure, and component sited in Washington, and WAC 296-150F-0210 attaches it only after the required forms and fees arrive and the unit passes final inspection. RCW 43.22.470 lets the department delegate all or part of that inspection duty to a local enforcement agency. Compare RCW 43.22.335, which defines a manufactured home as a single-family dwelling required to be built under the national manufactured housing construction and safety standards act of 1974.

Example

Dana and Paul Restrepo buy a two-acre lot outside Ellensburg for $118,000 and order a three-module, 2,040-square-foot home from a factory across the state line. The plans go to Labor and Industries for approval, the modules are built and inspected on the line, and each one leaves the plant carrying its insignia. In April a crane sets all three on a poured foundation in a single day. A local crew ties in the roof seam, the siding, the utility connections, and a garage that is framed on site. The finished cost lands at $431,000 including the lot. When the Restrepos refinance two years later, the appraiser pulls three site-built Comparables within four miles, at $438,000, $452,000, and $419,000, and makes no adjustment for factory construction, because the finished house meets the same State Building Code those three had to meet.

Common Mistakes and Exam Traps

• Modular and manufactured homes are both prefabricated, and that shared trait is what makes the pair a favorite distractor. The dividing line is the code: modular follows the state building code, manufactured follows the federal standard.
• A modular home is not panelized construction. Panel construction ships flat wall sections to be raised on site, while modular ships three-dimensional boxes that arrive largely finished inside.
• Set on a permanent foundation as part of the land, a modular home is real property. An answer treating every factory built dwelling as personal property is wrong.
• Washington statutes say factory built housing, not modular home. A Washington question about factory built housing is asking about this same category.