The thing about a house, when a person buys or builds one, is its permanence. It is probably the most durable good a man is likely to get in his lifetime, other than the ground it is built on. Almost anything else—a car, a binder, a suit of clothes—is expected to wear out in a few years. But a man's home, his cottage or mansion or dream house, is expected to survive the ages.

Into this market has come the prefabricated house. No mystery need be attached to the prefabricated house; the prefabricator has simply moved part of the building operations under roof and developed machinery to do them. Presumably, this shift of operations combines the advantages of machine speed and accuracy with the elimination of the factor of weather and lowers the cost of many building jobs otherwise done with hand tools at the house site.

According to his wishes and means, the individual prefabricator often uses some of the newer materials in his designs—moistureproof plywood, insulation, sheet-type building boards, spray-type paints and varnishes, and so on. The builder of the conventional houses also uses those materials, but the principal material for both conventional and the prefabricated houses is wood. Through economies of factory operations and more efficient engineering design, many prefabricators figure they can shave 10 to 20 percent off the cost of a conventional house of the same size and turn out a product just as good or better.

To date, however, the makers of prefabricated houses have had difficulty in convincing the buying public of the quality of their product. As these manufacturers are well aware, the buyer of a house, like any other buyer, prefers something with a proved record of service. Prefabricated houses are too new to have a long record.

Prefabrication got its real start during the 1930's but most prefabricated houses are much younger than that. Moreover, some prefabricated housing that was rushed out during the war to meet suddenly critical needs of defense workers was designed for temporary use, 5 years or less, and sometimes used inferior or substitute materials that somehow performed their emergency job but subsequently developed obvious structural ailments. The fact that some conventionally built war housing suffered similar warp, decay, and structural weakness often was not given equal consideration because conventionally built housing has a long history of durable value to offset the shortcomings of the wartime structures of its kind.

About 35,000 or more prefabricated houses were produced by some 200 companies in 1947. This was about 4 percent of the total 1947 output of the housing industry. A notable point is that a builder of conventional houses is considered relatively successful if he puts up 10 houses a year, but a number of prefabricators turn out that many or more a week, and the plant is small indeed that does not assemble the parts for at least one every workweek.

Prefabricated houses are appearing in many communities of the Nation. As these houses continue to serve their purpose through the years, public confidence in the product of house factories will be guided. Perhaps some day soon the house buyer, like the car buyer, will pick out his make and model on the basis of the maker's reputation. Meanwhile, however, the potential customer needs more specific signposts of quality on which to base his decision to buy or not to buy.

Two general kinds of prefabricated houses are being offered today. One is the semiconventional house, the parts of which—wall, ceiling, floor, and perhaps the roof sections—are of conventional size and are preassembled in a factory.

The other is the so-called stressed-cover, or stressed-facing, house, the panels of which usually consist of plywood or some other sheet material bonded with glue to a framework of smaller studs, joints, and rafters. This type of construction was first developed at the Forest Products Laboratory in 1934. On the Laboratory grounds today stand two 12-year-old examples of it; they appear as sound as ever.

The panels of either kind of prefabricated house may contain insulation, vapor barriers, electrical wiring, and other installations. Between the two basic types are many modifications that result from the adaptation of new materials and production methods to one or the other type.

Perhaps the first inquiry the prospective buyer can make is whether the particular house has been approved for his locality by the Federal Housing Administration, a Government agency that requires minimum standards of construction for loan-insurance purposes. The standards are fairly uniform, but in certain respects they vary somewhat for different parts of the United States. For example, thermal-insulation requirements differ according to climatic conditions of particular regions; a house needs better insulation in Minnesota than in Florida.

Further, the buyer can avail himself of certain technical guideposts that indicate the quality of materials, workmanship, and design.

The quality of a prefabricated house is compounded of good materials as well as technical skill and suitable factory conditions. An example is given by the stressed-cover, or stressed-facing house, which is manufactured by a growing number of prefabricators.

The maker of stressed-facing houses often uses plywood for his panel covers or facings. Because the strength of those panels depends largely on the plywood (as contrasted with the conventional frame house, whose strength depends primarily on the framework of studs, joists, and rafters) the quality of the plywood is important. Especially if it is used in outside walls and roofs, it must be highly water-resistant. Such plywoods are known as exterior grades, and moisture will not delaminate them.

The fact that stressed-facing panels are glued together emphasizes the need for using well-seasoned lumber and dry plywood in their manufacture. Insufficiently dried framing lumber will put excessive strains on the glue joints when it dries further, probably while in the house structure; it may even warp the panel out of shape. The good manufacturer, therefore, not only buys dry lumber and plywood, but stores it carefully at his plant in a protected indoor location. He does the same with his finished panels until they are transported to the building site. Also important is the glue that holds the facings to the panel framework. Synthetic-resin glues of the phenol, melamine, or resorcinol type are preferred. Of these, only the resorcinol glues can be cured adequately at room temperatures; when phenols or melamines are used, the panels must be put in a steam-heated or electric press or a heated curing chamber to set the glue.

Properly made panels must have well-machined, smooth, and uniformly sized framing. If two framing members meet at a corner and do not lie flush so that the plywood will be flat against both, for instance, a good glue bond cannot be made. There will be a weakening gap at this point. Too many such gaps in a number of house panels can seriously affect the structural soundness of the building. An indication of good quality in manufacture is the absence of such gaps in the glue bond between plywood and framing.

The way the plywood is attached is also to be noted. If it is nailed to the framework, the nails furnish the only pressure to hold the plywood to the framework while the glue cures. Consequently, to assure uniform pressure, they should be spaced evenly and not more than 4 to 6 inches apart. The thinner the plywood is, the closer the nails should be spaced.

Panels should have vapor barriers, usually sheets of asphalt-treated paper or aluminum sheet materials, which block passage of water vapor from the warm interiors of houses toward the outside in winter. Such vapor movement is hazardous because the vapor may be chilled inside the panel and condense as frost, which later melts and damages exterior paint and interior ceiling finish, and may even encourage decay inside the panel. For that reason, vapor barriers should always be on the warm side of wall, ceiling, roof, and floor panels; they are unnecessary in interior partitions, second-story floor panels, or first-floor panels over heated basements.

Insulation is usually installed where the climate requires it. Some types of insulation, called blanket or batt insulation, come with a paper backing that may have been treated for vapor resistance; with such insulation a separate barrier may not be needed. Reflective insulation, such as metallic foil, is a good vapor barrier. Barrier materials should be well sealed to panel framework.

The prospective buyer can learn a great deal about quality if he watches the workmen assemble a house. A look at the foundation is in order, particularly if the house has no basement. In such houses, whether prefabricated or conventional, the space underneath the floor is called a crawl space and should be at least 18 inches high between ground and subfloor. This space should be ventilated by openings resembling basement windows in the foundation walls—all such openings should be wide open at least during the spring, summer, and fall to insure ventilation. Without such openings, dangerous decay conditions can develop in the subfloor structure. Preferably, the ground of the crawl space should be covered with roofing paper and several inches of gravel.

At the building site, panels can be inspected for good workmanship to see if they are true and well-made, with continuous glue joints between framework and facings. How well they fit together while the walls, floors, ceilings, partitions, and roof are being assembled is a clue to their manufacture. Do panels join well together at room corners and at the joints where wall, floor, and ceiling meet? Small gaps here are to be expected and can be hidden with molding and other trim, but the finished job should be neat.

In most modern houses, both prefabricated and conventional, there is an unfinished attic space between ceiling and pitched roof. Insulation is laid over the ceiling. The attic space is another source of danger from moisture vapor. A vapor barrier should be laid under the insulation. The attic should also be ventilated; this is usually done by means of louvered openings in both gable ends to permit air to pass through the attic space. The openings should be ample in size; they are more likely to be too small than too large.

An inspection of the exterior of the finished house can be helpful. In particular, all the exterior joints between panels, especially the horizontal joints, should be especially well made and protected with metal flashing, drip caps over windows and doors, and similar devices for blocking the penetration of rain water. A roof with a good overhang has advantages.

The critical buyer may want to check on several other details, but he should bear in mind that the basic factors are good materials, and good workmanship, and good structural design. Each depends on the others and complements them. In building with wood, the designer keeps uppermost the fact that moisture can be his greatest enemy and he designs accordingly. With the proper safeguards, he knows that wood construction can be entirely satisfactory, safe, and economical, whether prefabricated or conventional.