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MANUFACTURED HOUSING IN NONMETROPOLITAN AREAS:
A DATA REVIEW

© Housing Assistance Council, 1996

Permission is granted ONLY to nonprofit community-based organizations to reproduce and/or adapt this document, and only for their own use.

APPENDIX B:
WHAT IS MANUFACTURED HOUSING?

Almost all housing built in the United States includes some manufactured components. It has been estimated that 95 percent of all homes today utilize at least some factory components, such as roof trusses, even without counting windows, doors and cabinets.⁵² Use of manufacturing processes in house construction could be viewed as a continuum from a few, specific prebuilt components to complete structures ready to be set into place. In practice, however, some terms and regulations define specific points along the continuum. 

At one end of the continuum is the site-built home using standard prehung windows, doors, and roof trusses that have been fabricated in a factory. Kit, or precut, homes are an old variation in which all the parts of the completed house are cut and prepared in a factory, ready to be constructed at the site. In 1908 Sears, Roebuck and Company began selling complete kits in its catalog, and sold about 100,000 of them until 1939. A number of specialized companies now offer kits of different types. Kits allow building even in remote locations where choices of building materials might otherwise be limited. Kits can include some assembled parts. Log and dome homes often are sold as kits and may include some panelized components.

Panelized building systems that use wall panels assembled in a factory are next on the continuum. These can be described as open wall, which have only structural members and outside sheathing, or closed wall, in which plumbing, wiring, insulation and inside finish are installed at the factory. Within these categories there are many gradations of completeness of panels. Panels can be combined in a wide variety of sizes and designs, and allow a great deal of customization. A key distinction of panelized systems is that the panels can be shipped flat, which is less costly than moving three-dimensional components. They can be assembled very quickly on a prepared foundation at the house site, thus minimizing exposure to damage from weather, theft, and vandalism. Fewer skilled trades people are needed than for site-built housing.

Modular building systems are the next step up in using manufacturing processes to build houses. Modules are assembled in three dimensions at the factory and may be more than 90 percent complete. They are towed to the site on flat bed trailers. At the site, those three-dimensional boxes are stacked or put together in a variety of ways. Modular construction can be useful in remote areas where getting trades people to the site in a timely manner is difficult and expensive, if the shipping distance from the factory is not too great. Developers can find cost-cutting efficiencies without sacrificing quality when a number of units are erected at one site. According to the National Association of Home Builders, modular units have been used increasingly in high-wage urban areas of the eastern metropolitan corridor. Because modular homes are three-dimensional, they are more difficult to ship than raw construction materials, and need to conform to highway size limitations. 

The term "building systems" is used to include modular, panelized, and some kit houses. All of these must still conform to local building codes. Since one factory is likely to sell regionally, units built there are likely to conform to the building codes in all the surrounding jurisdictions. (In contrast, a site-built home is built to conform to just one building code.) All can use factory volume and sophisticated machinery to save money on architectural design, labor, and materials. The factory environment offers the possibility of strict quality control. Panelized and modular homes built in the controlled environment of a factory minimize exposure to weather damage during construction. Once in place, these houses are virtually indistinguishable from site-built houses. 

Panelized and modular units have not always been accepted by local inspectors who did not observe the construction or see what quality of materials were inside completed components. (Generally, states have agreements to accept the inspection of the home state after initial checks.) Therefore, many have been placed in nonmetropolitan or rural areas where there are often fewer building restrictions.⁵³ 

At the far end of the continuum is housing that is fully completed inside a factory. Units finished in factories were first produced as travel trailers, intended to be moved and intended for short-term occupancy. The terms "mobile home" and "trailer" continue to be used widely, even though the modern manufactured house is difficult and expensive to move. As the lower cost of trailers attracted year-round residents, concerns about housing quality and safety moved the U.S. Congress to pass the National Manufactured Housing and Safety Standards Act of 1974, which regulated manufacture and established a preemptive building code. The United States Department of Housing and Urban Development (HUD) was charged with administering the Federal Manufactured Home Construction and Safety Standards (FMHCSS), also known as the HUD Code. That Code took effect in 1976 and preempted state and local building codes. Manufactured housing is the only kind of housing regulated by a federal building code. Some sources make a distinction by referring to units built before 1976 as "mobile homes" or "trailers," and those built since to conform to the HUD Code as "manufactured housing." The industry group that builds and sells such housing strongly prefers the term "manufactured housing." That term does not include kit, panelized or modular housing.

A key distinction of manufactured housing is that it must be attached to a permanent chassis to which wheels are attached to tow the house to its site. Once there, the wheels and hitch may be removed and the unit should be leveled and anchored or attached to a permanent foundation (with or without skirting attached around the lower edge). The chassis remains in place.

Manufactured housing first was made only in single widths, as rectangular structures 8 to 14 feet wide and up to 40 feet long that could be moved on the highway. They had a distinctive, box-like appearance and a slightly rounded roof line that kept the total structure low enough to move under highway overpasses. Later, double- and even triple-width units were developed that were moved separately and then attached at the site. These had more space and looked more like conventional single-family housing. Pitched roofs were designed that could be folded flat for transport. 

While single-width manufactured homes made up 71 percent of those placed for residential use in 1984, by 1993 only 52 percent were single width. Multi-width units were most popular in the Western region of the United States, where they made up 68 percent of the market. In all other regions, single-width units predominated. Single-width units are smaller and less costly. The average new single-width had 1,065 square feet of space and sold for $21,900 in 1993 (without a lot), compared to the average multi-width that had 1,525 square feet and cost $39,600 (without a lot).⁵⁴ Approximately 100 corporations manufactured HUD Code houses in about 250 plants nationwide.⁵⁵

Also fully manufactured are recreational vehicles or travel trailers which are intended for short-term occupancy. They are smaller than manufactured homes and not intended for permanent housing. Such recreational vehicles are not regulated by the HUD Code and are not considered housing for regulatory purposes. People do live in them, however, either by lifestyle choice or because they cannot afford other housing. They should be considered "mobile homes" in the AHS/Census definition of the term, and so should be included in data reported in those surveys.

The idea of building houses in factories has been around for many decades. Doing so can save time and money and use materials more efficiently than building on-site. Fewer skilled trades people and subcontractors are needed. Construction does not depend on weather. Nevertheless, many attempts to develop factory-built houses have not been successful, for a variety of reasons including regulation, acceptance of the product, and marketing. Some growth has occurred in the industry, subject to the fluctuations in the housing market. Automated Builder magazine has estimated that the number of panelized units built rose from 399,000 in 1983 to 548,000 in 1993. The number of modular homes increased from 62,000 in 1983 to 91,000 in 1993. These numbers combine to equal almost half the 1,288,000 single- and multi-family housing starts in 1993. The number of HUD Code manufactured homes constructed nationwide decreased from 295,000 to 250,000 from 1983 to 1993.⁵⁶ 

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