I had known of Richard Neutra's Kaufmann House, in Palm Springs, Calif., for years, but only when I finally stood inside it did I realize how powerful an impact this modernist classic makes, how fully and brilliantly it blurs the distinction between inside and outside. In most of the iconic photographs, the house appears to sit alone in the vast open spaces of the desert. Today, however, the surrounding area has been built up, and the site I found was relatively small, its primary connection not with the expanse of the desert (though you are conscious of the mountains and the totality of the landscape) but with the house's own, more conventionally sized lawns and terraces. Another thing I didn't anticipate was how important wood and stone are to this house, to achieving the complex series of counterpoints that Neutra pulled off here—harmonic juxtapositions of mass, of light, of solid and void, of rough and smooth textures.

All of this would not have been as apparent had the Kaufmann House not been lovingly restored, an effort that was as ambitious, in its way, as the creation of the house in the first place. The house had been treated terribly for years—it had gone through a couple of owners, one of whom had tried to turn it into a conventional residence, expanding it in ways that suggested no understanding whatsoever of what Richard Neutra was trying to do when he designed it in 1946. But the challenge went beyond ripping off the mistakes and stripping the house down to its essence. Much of that essence had to be re-created; it was not as if the original house were sitting, undisturbed, underneath the alterations. Windows, doors, floors, partitions, all kinds of elements needed to be re-created. Furniture needed to be found again, or remade to original specifications. And since architects are only now beginning to look at modernist buildings with the preservationist's eye, some of the challenge was in trying to determine what we might call a system, or even an ethos, of modernist preservation.

Some of the issues involved in preserving modern buildings are unique to the period in which the structures were built, such as the technology of flat roofs or glass-window walls. When New York City's Lever House, the great glass skyscraper on Park Avenue, was restored, Skidmore, Owings & Merrill, the architects, had to find a replacement for the original glass curtain wall that would look the same but perform completely differently, since the old wall from 1952 was thin, almost flimsy, and air leaked through it like a sieve. It didn't come remotely close to meeting the energy requirements of today. But if the new glass didn't look like that old, badly functioning glass, the appearance of the building would have changed dramatically.

Skidmore created an insulated, double-layer glass wall that looks pretty much like the original. And the restoration of the Kaufmann House has allowed it to look almost exactly as it did when Edgar and Liliane Kaufmann took possession of it in 1947. Though the technical issues of glass walls are a lot different from the technical issues of shingles or adobe or stone, the philosophical questions and dilemmas underpinning modernist preservation are familiar. Do you restore a building to the way it looked when it was new, or to a particular period that was most important in its history? Or do you seek to show the passage of time, and the layers of time, that a building reflects?