Traditional French residence designed by Pierre Chareau

NO house in France better reflects the magical promise of 20th-century architecture than the Maison de Verre. Tucked behind the solemn porte-cochere of a traditional French residence on Rue Saint-Guillaume, a quiet street in a wealthy Left Bank neighborhood, the 1932 house designed by Pierre Chareau challenges our assumptions about the nature of Modernism. For architects it represents the road not taken: a lyrical machine whose theatricality is the antithesis of the dry functionalist aesthetic that reigned through much of the 20th century.

Its status as a cult object was enhanced by the house’s relative inaccessibility. For decades it was seen only by a handful of scholars and by patients of a gynecologist whose offices took up the first floor. Later it was mostly used as occasional guest quarters for friends of the doctor’s family, who had long since settled into a traditional 18th-century apartment across the courtyard.

So when I heard over dinner here with some friends a year or so ago that the family had sold the house to an American entrepreneur, I was astonished. My dinner companion, an architect who had never met the new owner, lamented the sale as evidence of France’s cultural decline, akin to the construction of Euro Disney. Waving a dismissive hand, she invoked the cliché of the ugly American, pockets stuffed with dollars.

As it turns out, although the buyer, Robert Rubin, made his money on Wall Street, he is far from a crass trophy hunter. After buying the house, he embarked on a painstaking renovation of its intricate — and for its time, ingenious — mechanical systems. He enlisted a corps of architectural historians and graduate students to decipher its secrets. With the first phase of the renovation completed, he plans to open it up eventually for limited tours. In his loving devotion to the house and its historical particulars, he has emerged as a role model for those who seek to preserve an architectural relic without turning it into a mausoleum.

Mr. Rubin, 54, is a born collector. He restored his first car, a Jensen Healy, when he moved to New York City in his early 20s. After racking up money as a commodities trader in the mid-1970s, he turned his eye to bigger prizes, like a 1960s Ferrari 275 GTB and later a rare 1933 Bugatti that had once belonged to King Leopold of Belgium. His fascination with industrial objects eventually led him to the works of Modernist architects like Jean Prouvé and Chareau, whose creations were elaborate Machine Age fantasies.

Approaching his new subject with the zeal of a scholar, Mr. Rubin went back to school in 2001, enrolling at Columbia University’s graduate school of architecture at the age of 48. He worked as a teaching assistant for Kenneth Frampton, the architectural historian who wrote a celebrated textbook on 20th-century Modernism.

Around the same time Mr. Rubin bought Prouvé’s Maison Tropicale, a prefabricated metal shelter conceived in the late 1940s as a prototype for affordable housing in colonial Africa and later erected in the Congo. After a methodical restoration, he organized a series of exhibitions on the Prouvé house, shipping it to Yale and to the Hammer Museum in Los Angeles. Last year he donated it to the Pompidou Center. (By contrast the hotelier André Balazs recently bought a version of the Maison Tropicale at Christie’s, for $5 million and plans to make it the centerpiece of a Caribbean resort.)

Yet nothing Mr. Rubin had collected up to this point could compare — in scale or in the weight of responsibility — to the Maison de Verre. The house is often compared to another early-20th-century masterpiece, Le Corbusier’s Villa Savoye. Both houses were built in the brief period between the two world wars, the high point of classical Modernism. Both embody that movement’s obsession with hygiene, and the fiercely held notion that a house could function as a tool for physical and psychic healing. But while Le Corbusier’s masterpiece was intended as the expression of a broad vision — a philosophical rejoinder to the squalid disorder of the medieval city — Chareau’s ambitions were more humble.

Born in 1883, he began his career as a draftsman for a traditional English furniture maker in Paris. By the early 1920s he had designed the interiors of some elegantly appointed apartments for wealthy clients and was mostly admired for his furniture designs, elaborate wood and metal pieces with movable parts that reflect a taste for refined machinery.