Size Mattered: Remnants of the Golden Age of New York Mansions Still Dot the UES

A TOUR OF THE MANSION AT 12 EAST 79TH STREET reveals a building caught between two worlds. There are, of course, the home's historic roots. It was built between I901 and 1903 as part of a 56-foot-wide pair of houses for Charles W. Ogden, a millionaire who made his fortune in real estate, and his sister Mary. Matching facades decorated with brick, Ionic porticos and lime-stone trim meant to reflect the family's wealth-such details remain intact to this day. Also intact inside Mr. Ogden's abode, at No. 12, are elaborate plaster designs on the ceiling, a salon spanning the 28-foot width of the house and oval, wood-flanked meeting room.

Despite remnants of its single-family glory, this building is no longer a place anyone calls home. Today it belongs to the School of Practical Philosophy-you may know it by its subway ads-which bought it in 1975. A raised office space was built in the front parlor. The massive bedrooms lost most of their interior details in their transformation to classrooms. And at some point, two extra stories were added atop the roof. The school's headquarters was previously on the market, asking $51 million in 20I4, offering the opportunity for a buyer to transform it back to its residential splendor. No one bit, so the building remains something between a school and a mansion. It's an outcome probably not envisioned upon its construction during the Upper East Side's "mansion boom" of the late 19th century, but one that became commonplace as the appeal of mansion living eventually dwindled.

During said boom, the property's location, between Fifth and Madison avenues, was described by The New York Times as "the choicest plot of land for elegant single-family dwellings in New York City." That's due to one man, railroad magnate Henry H. Cook. In 1880, Cook purchased the entire block from Fifth to Madison, between 78th and 79th Streets, for $500,000. He then set strict building restrictions, declaring only private homes could be built on what became known as the Cook Block. (The restrictions survive today.) He also subjected incoming families to a rigorous admissions process, ensuring only elite New Yorkers as his neighbors.

Cook built his own massive stone mansion, now demolished, on the corner of 78th Street and Fifth Avenue. Others, like the Stuyvesants, Dukes, Whitneys and Ogdens, followed suit. This mansion rush-with families using intimidatingly lavish architecture as a status symbol-marked the beginning of the Upper East Side's reputation as the most elite neighborhood in New York. Though the Dakota had recently been built on the Upper West Side and would soon usher in a new era of apartment living for the wealthy, people of means for the most part continued to live in mansions, setting a standard for prestige that has never quite disappeared.

"Previously, there had been some development in the area, but mostly of modest brownstones," said New York historian and author Francis Morrone, who called the Upper East Side the "next destination in the uptown movement" of New York's wealthiest, who were seeking greener pastures as once-fashionable downtown neighborhoods started feeling too crowded and overdeveloped.

The undeveloped land off Central Park ensured enough room for New York's grandest homes-so grand that the stretch of Fifth Avenue, beginning around 50th Street, became known as "Millionaire's Row." The Vanderbilt family, who made their fortune in railroads, bought up all the property on Fifth Avenue at 57th Street to construct a palace that occupied the entire block and held 137 rooms, 37 bedrooms, 16 baths, a library, numerous salons, a baronial dining room, smoking room and ball-room. The William B. Astor house, on Fifth Avenue and 65th Street, was a double mansion designed to rival the Vanderbilts. The entertainment spaces could be joined into a single, magnificent ballroom that was said to be the largest in New York. Ballrooms were a requisite for wealthy families-"They built ballrooms even if they had no friends," Mr. Morrone said.

In 1898, Andrew Carnegie made the "questionable" move up to 90th Street from his brownstone mansion, located next to the Vanderbilt chateau. He found the behavior of his Millionaire's Row neighbors distasteful, and also wanted open space for a garden surrounding his new digs. The result was a 64-room country estate surrounded by a cast-iron fence and the largest lawn and garden in New York. Carnegie also started buying land in the area so "he could personally control the development of the neighborhood:' said Mr. Morrone.

Otto Kahn, for example, bought land from Carnegie to build an 80-room French limestone mansion. The Kahn family asked renowned architects C.P.H. Gilbert and J. Armstrong Stenhouse that no expense be spared in their home design. ("It's a sin to keep money idle," Kahn had stated.) Indeed, "these were fantastically rich people," said Mr. Morrove. Such families only worked with "top-of-the-food-chain architects" trained at the Ecole des Beaux-Arts in Paris. "With a house, you put yourself on display right on the street:' Mr. Morrone said, "When New Yorkers lived in private houses, a lot of the general public knew that sort of thing. They knew which Vanderbilt lived in which house." Mrs. Astor's parties were also legendary-her social index, known as the "Four Hundred," referred both to the New Yorkers who mattered in society and how many guests could fit into the ballroom.

This Gilded Age period proved to be exceptionally short lived. "It was inevitable that many of the homes would be replaced:' said Mr. Morrone. The reasons for this are varied. After World War I, the rich started to feel like it was "unseemly to live in mansions," he said.

Lifestyles also changed and entertainment became more casual-"casual for the I percent," Mr. Morrone added-diminishing the need for sprawling ballrooms. The first apartment building to replace a private mansion in the neighborhood was 907 Fifth Avenue in 1919; architects instead promised to build "mansions in the sky" for wealthy New Yorkers. And when John D. Rockefeller moved into a co-op at 740 Park Avenue in 1937, "it meant anyone could live in an apartment:' said Mr. Morrone.

The arrival of apartment buildings not only changed the landscape of the Upper East Side, it changed the meaning of being rich there. "The facade of an apartment is not a reflection of you like a house is a reflection of you:' Mr. Morrone noted. Many of the elite co-ops had understated, limestone facades-wealthy New Yorkers were now part of a private, almost secretive building. The desire to make a statement with ostentatious, oversized mansions had all but vanished by the 1920s.

Most of the Millionaire's Row mansions along Fifth Avenue were demolished-the Vanderbilt compound made way for Bergdorf Goodman; the Astor Mansion was replaced by Congregation Emanu-El of New York. But along Central Park East and the surrounding side streets, some remained. The grand spaces actually worked for a variety of things: muse-ums, galleries, libraries, schools. After the U.N.  opened its headquarters on the East Side in 1952, many countries bought mansions to use as showcase-worthy consulates. Andrew Carnegie's country villa is now the Cooper-Hewitt National Museum of Design; Otto Kahn's home belongs to the private school Convent of the Sacred Heart; 12 East 79th Street, of course, belongs to the School of Practical Philosophy.

The upscale boutique Hayward House found an unlikely home for its flagship store on the second floor of the former Grosvenor Atterbury Mansion at 131 East 70th Street. "We were looking for something different, something unique," said John Goldstone, co-founder of the company with his wife, Marin Hopper. Hayward moved in in 2014 after a renovation that restored details like wood paneling carved with acorns and oak leaves, Tiffany glass, a hand-painted gold-stitched ceiling and a fireplace frenzied with fretwork. The couple also bought a condo on an upper floor of the mansion, which had been converted to apartments. "There were some anxieties since this was an unusual approach for a retail space," he said. "We wondered, 'are people gonna come?''' Ultimately the building proved an appealing home base for the company and a draw for customers. "It's been a terrific honor to be installed within that space," Mr. Goldstone said.

And in today's strong real estate market, brokers hope these mansions may still prove appealing as grand, Single-family homes. 'As far as scale, proportion and provenance-this is the only place you can get it," said Corcoran broker Daniel Douglas. "It's something you can't find with condos, with their dog washing stations, rock walls, God knows what else."

Stan Ponte, a Sotheby's broker marketing the 14,000-square-foot Clarence Whitman Mansion at 7 East 76th Street for $50 million, said, "We've all heard the talk about the glass towers, and the question marks around them. I think luxury in New York real estate is pivoting to 'best in class properties' that cannot be easily replicated. These grand dame townhouses are exactly that." He added, "The number of limestone mansions on the Upper East Side does not increase. That's where the value comes in."

With limited space and landmark status protecting much of the existing architecture, those seeking their own mansions have to get creative. On East 81St Street, Madonna combined three townhouses to form a single property surrounded by a IO-foot gate. In 2007, artist Jeff Koons purchased two townhouses at 11 and 13 East 67th Street for $32 million and started work on his own 19,000-square-foot mega mansion. Former Mayor Michael Bloomberg, who lives in a townhouse at 17 East 79th Street, has spent years buying apartments in the co-op building next door, knocking down walls and gradually combining the two properties.

Stephen Wang, the architect combining' three townhouses from II-15 East 75th Street into an 18,ooo-square-foot mega-mansion for the Russian billionaire Roman Abramovich, said his firm has received an influx of Upper East Side townhouse projects in recent years. They are easier to snatch up than grand mansion properties, and are fairly flexible for wealthy buyers who want to add perks like swimming pools, elevators, gyms, spas and roof decks. Not that these renovations are a walk in the nearby park. The Department of Buildings denied Mr. Abramovich's plans to combine the townhouses this March; once work permits are approved the project still needs approval from the Landmarks Preservation Commission.

When developer Daniel Straus purchased a multi-building site along East 74th Street in 20l0, "the focal point was the mansion [at 33 East 74th Street),..there are very few mansions like that on the Upper East Side." Mr. Straus built out IO condo units between a collection of brownstones on site and the mansion, which was built in 1901 for the banker Julian Wainwright Robbins and his wife, the niece of Cornelius Vanderbilt. The mansion holds two units: a four-story,10,000-square¬foot condo that entered contract with a mid-$40 million price tag and a 6,30o-square-foot triplex that closed for $31 million. "The two units allow for townhouse living within a mansion, with all the perks of a condo," Mr. Straus said.

Originally, he listed the unrenovated mansion as a single-family property for $38 million, thinking someone might want to replicate the single-family grandeur of a Vanderbilt. "We were surprised," he admitted. "But the property was just that large ... we didn't have someone willing to take on all 17,000 square feet."