Monday through Saturday, mail-order catalogues pour through the slot in my front door, offering everything from lingerie to bird feeders. Any day now, I expect to receive one picturing manufactured homes. I would not be surprised if it came from Japan, rather than Sears Roebuck, with houses made by Honda, Toyota or Mitsubishi.

There is renewed interest in, and discussion of, manufactured housing in the United States. Depending on how you count, between one-third and one-half of all new dwelling units constructed in the United States can be classified as "factory built." Many are mobile homes, but a growing percentage is built on conventional subdivision lots in diverse locations.

Manufactured housing differs from conventionally built housing primarily in method and location of production. Factory or field built, the final products may be indistinguishable.

Conventional homes are constructed at the site by teams of skilled workers using hundreds of types of manufactured materials. These materials -- lumber, concrete blocks and bricks, hardware, roofing shingles, windows and doors -- are assembled into larger components such as foundations, walls, floors, roofs and partitions by a combination of hands and machines. Manufactured homes generally use the same basic materials, but they are assembled into larger components in factories prior to site delivery. In either case, builders still must prepare roads, grade lots, install utilities and excavate and build foundations to support the house's superstructure.

Manufactured houses vary widely in both architectural character and in the extent of factory preassembly. Mobile homes best exemplify total, industrialized fabrication. Emerging from the plant, they are ready for occupancy and only need to be placed on a lot somewhere. Interiors are completely finished with cabinetry, appliances, plumbing and heating systems.

Prefabricated modular or sectional homes likewise leave the plant nearly ready for occupancy. Some are finished inside and out, while others may be shipped as shells, to be finished at the site in accordance with builder and customer preferences. Modulars often are fabricated and transported in two or three sections that are joined together at the site.

Panelized homes avoid factory assembly of volume-consuming, three dimensional modules. Instead, predesigned housing units are manufactured as planer sections -- floor panels, wall and partition panels, and roof panels -- which are then stacked, crated and shipped for field assembly. If panels are large enough, they can include windows and doors, plumbing, electrical wiring, insulation, and interior and exterior finishes.

Panelized home packages also can include cabinetry and equipment for kitchens and bathrooms. Being more efficient to store and transport, panelized housing systems may have interchangeable components, allowing greater design and construction flexibility in configuring assorted home models.

Some prefabricated homes are made and shipped in small pieces as veritable kits. The manufacturer essentially designs and builds a prototype house, disassembles it, counts and measures every piece, and then reproduces and packages duplicate sets. Joists, studs, sill plates, beams, columns, siding, sheathing and other ingredients are pre-cut, inventoried, labeled and delivered to customers who only need to follow manufacturers' assembly instructions. A few prefabricated-home-kit manufacturers will even design custom homes, within prescribed geometrical limits. Today, buyers can purchase everything from log cabins to bungalows to barns.

Why build a home totally, or partially, in a factory? Why are the Japanese, along with the Europeans, so keen on industrialized housing? Manufactured housing proponents cite several key factors: Factory production facilitates ordering materials in volume, their handling and coordination, and quality control. Advance bulk purchasing can eliminate problems of material shortages while yielding economies of scale. Factory production makes construction less dependent on weather, a critical consideration in very cold or wet climates. Thus, year-round, consistent factory output can be maintained. The amount of labor required can be reduced and less-skilled laborers can be employed. Factory production permits standardization of operations, automation and procedural specialization to which relatively unskilled personnel can be trained. With computers and robots, some tasks may require no labor at all. House manufacturers potentially can reach much larger geographic markets because of transportation systems; traditional home buiding usually focuses on local markets linked to local supplies of labor and materials.

Despite the apparent advantages of factory construction and the potential for getting more house for the dollar, future cities and suburbs are unlikely to look like mobile-home parks. Indeed, failed attempts to industrialize housing may outnumber successful ones. The field-built house is not yet an endangered species.

NEXT: Problems of prefabrication