Putting up a house in a single afternoon

After Bill and Mary Bernie bought their secluded lot in this New Hampshire town a year ago, they had the home of their choice put up in a hurry - in a single afternoon, to be exact.

Except for the poured slab foundation, the house was not erected on site; rather, it was trucked in in much the same way as the furniture that arrived the following day.

It came in two halves that were set in place, bolted together, and carpeted all within a matter of hours - 1,500 square feet of living space containing three bedrooms and two baths. Once the carpeting was rolled into place, Mr. Bernie says, you couldn't tell where one half ended and the other began.

The Bernies, like one-third of all new-home buyers in the United States last year, had opted for a manufactured home - one made in a factory rather than built piece by piece on the lot. They chose it because of the speed of occupancy (compared with site-built housing) and the value for the dollar available in the modern manufactured home.

As the Bernies' 28-foot-wide home clearly indicates, the factory-made house has come a long way since its founding in the late 1930s.

What started as a tiny house on wheels behind the family car quickly became the long, slender mobile home - the ''tin can on wheels,'' according to its detractors - that met the housing needs of largely low-income groups in mobile-home parks and rural areas. Increasingly of late, it has evolved into housing that is less and less distinguishable from its conventional site-built counterpart.

Indeed, modern manufactured housing (either modular that sits on a conventional foundation, or mobile in which the wheels become the foundation) comes with standard cladding (vinyl or wood siding, cedar shingles, and stucco to name some options), pitched roofs, cathedral ceilings, double widths, and even double stories.

But while the look is turning conventional, the cost has remained very competitive. Where the average cost, nationwide, of a site-built home in 1982 was $39.25 a square foot, the average cost of a manufactured home was $19.22.

''The construction costs for comparable 1,500-square-foot units are 34 percent lower using manufactured-housing, factory-built techniques, rather than site-built traditional approaches,'' according to a survey by the US League of Savings Institutions.

The cost advantage of manufactured homes, combined with improved looks and the slow breakdown of old misconceptions and their accompanying prejudices, will earn the product an increasing share of the market, the Manufactured Housing Institute asserts. Deliveries of factory-built homes last year jumped 24 percent over 1982 figures for a total of 295,079.

Currently, single-section manufactured homes range from 700 square feet of living space to 1,100 square feet and cost from $10,000 to $30,000 and up; multisection homes (two, three, and sometimes four sections) are considerably larger and range from $17,500 to $50,000. These prices are for a partly furnished home that includes carpeting and appliances but not the land.

At the lower end, in what the industry refers to as the superaffordable price range, the old-style, flat-roofed mobile home is still being made, coming in as low as $7,500 in 1982. But where the old-style mobile home tends to depreciate over the years (though at a much slower rate than the family car), the modern style, erected on a suburban lot, appreciates in value like any other real estate.

The controlled conditions of a factory are the principal reason manufactured housing comes in at such a competitive price. Construction, unaffected by rain, snow, heat, or cold, is possible year round.

Modern assembly-line production techniques mean that more house can be built in an hour than is possible at the site. Bulk buying by factories producing two or more homes a day means that carpeting, floor tiles, furniture, stoves, refrigerators, heating units, etc. are obtained at highly competitive rates.

''We buy more appliances in a year than the average furniture store ever does ,'' says a spokesman for Burlington Homes of Oxford, Maine, makers of the Bernies' home.

Since 1976 all manufactured housing has had to be built to the construction, durability, and safety requirements of the Department of Housing and Urban Development (HUD).

The effect on the industry, combined with a downturn in the economy, was dramatic. Within a year the 400 companies turning out mobile and modular homes had slumped to 170. A vast majority of the surviving companies were those that were quality-conscious even before the HUD standards became law. Today approximately 180 companies manufacture homes from 410 factory sites throughout the country.

Meanwhile, zoning barriers against the placement of manufactured homes, just because they are factory-built, still exist in many areas of the United States. But these are falling slowly.

Recently, New Jersey enacted legislation prohibiting municipalities from enforcing development regulations on manufactured housing different from those applied to other housing. Twelve other states - California, Oregon, South Dakota , Minnesota, Nebraska, Tennessee, Indiana, Kansas, Virginia, Florida, Vermont, and New Hampshire - had previously taken steps at state level to eliminate discriminatory zoning barriers against manufactured housing.

As this trend continues there will be less need for officials in the manufactured housing industry to display an old cartoon:

Two hillbillies are sitting in front of a tarpaper shack watching a modular home being moved in next door. ''There goes the neighborhood,'' says one.