Fitting new 'skins' on old structures

New ''skins'' are being put on a growing number of skyscrapers and other buildings across the United States. Instead of razing old buildings to replace them with new ones, architects and developers are stripping them down to their steel skeletons and rebuilding them inside and out.

Reskinning can produce modern buildings at 20 percent of the cost of new ones. ''Reskinning is getting to be more of an accepted alternative,'' says Randolph Thomas, vice-president of Jon Construction Inc., of Chicago. ''The best use in many cases is not restoring the old, but making an old building look new.''

Many cities are filled with old schools, warehouses, and skyscrapers that are structurally sound, but crumbling on the outside. The exteriors of those of historical significance are frequently refurbished to retain their original character.

Buildings with little historical interest are increasingly fitted with all-new interiors and exteriors.

Many older buildings are near central business districts, and thus attractive for recycling as office buildings. Zoning laws often hamper builders from replacing old buildings with taller ones. And recycling saves on demolition costs.

In some cases, the new skins are layered right over old ones. At the Meredith Corporation headquarters in Des Moines, an envelope of reflective glass was wrapped around part of the old, brick-face building.

Often, though, the buildings are stripped all the way down to their steel, or concrete, skeletons. By replacing thick exterior walls with new ones that are more energy efficient, though much thinner, developers can often increase the inside space and make the building more suitable for other uses. Two major projects under way in New York are the 1100 Avenue of the Americas Building, where a brick and limestone facade is being replaced by a glass and metal one, and the formerly brick-face Biltmore Hotel, which is being turned into a stone and glass office building.

Reskinning does have drawbacks. Architects and builders are not always sure what the skeleton will look like until they peel away the old facade. Architectural drawings of some structures are nonexistent; others are inaccurate. Then, too, a few steel frames twist and tilt when shorn of heavy old skins.

To some degree reskinning has been going on for many years. The practice spurted in the 1950s with the introduction of ''curtain walls,'' sections that could be fastened onto the outside of buildings, often to spiff up the facades of storefronts.

Now the process has gained impetus from high building costs and interest rates, as well as large tax breaks. ''In today's market, time is money,'' says Clemson University professor Lamar Brown. ''If you can retrofit, rather than start from scratch, you are way ahead.''