Townhouse Turnaround - NYTimes.com Sasha Maslov for The New York Times Doug Derryberry and Serena Mulhern with their children, Justice and Jane, in the townhouse they are renovating in Prospect Heights, Brooklyn. The New York townhouse has been through a lot since it began appearing in profusion in the 19th century. These stately buildings started life as single-family houses sheltering comfortable middle- and upper-class families and their servants. By the Great Depression, most had been chopped into single-room apartments, the unlucky among them getting the greatest wear, as rooming houses for the down and out. In the "60s, plucky young New Yorkers with more enthusiasm than cash began buying these down-at-the-heels beauties and spiffing them up for their families, usually retaining tenants who provided rental income and in many cases were impossible to dislodge. In the past few years, the historic townhouse has started to come full circle. Thanks to the growing appetite for larger and more luxurious private urban dwellings among people happy to pay upward of $10 million, many townhouses have been returned to the elegant single-family homes they once were. To the casual passer-by, the changes may be invisible. On the East and West Sides of Manhattan, in Greenwich Village and in large swaths of what is commonly called Brooklyn's brownstone belt, brick, brownstone and limestone facades encrusted with corbels and lintels continue to mirror a distant era. But these ornate fronts conceal profound shifts in occupancy, demographics and financial structure. Townhouses represent only a small fraction of the city's housing stock, but because they define certain beloved neighborhoods, the implications of their transformation are great - though whether the shift represents boon or blight depends on who is being asked. "These houses have always been commodities - they were built, after all, by real estate developers," said Patrick Ciccone, a preservationist who is preparing a revised edition of "Bricks and Brownstone," Charles Lockwood's landmark 1972 study of the New York townhouse. So returning a townhouse to single-family occupancy might be the most historically appropriate thing to do, given its original use. But, Mr. Ciccone added, in the process of such conversions, what may be sacrificed is the life and activity on the street produced by variety in the size, density and affordability of residences. "So what's good for one house," he said, "can also be bad urbanism for the city as a whole." This time around, a different breed of New Yorker is working the magic on these buildings. As tenants move or die off, many owners are reclaiming entire buildings. Perhaps most important, developers are doing the same, a process that often entails a gut renovation and high-end amenities (elevators and wine cellars de rigueur). Notwithstanding the rear glass walls increasingly common in retrofitted townhouses, the better to brighten dark interiors, many 21st-century buyers harbor an unexpected taste for Edith Wharton-style décor. They wax eloquent about coffered ceilings and mahogany wainscoting. Savoring a 19th-century aesthetic, they seek meticulously preserved period facades along with lush interior details like carved moldings and wood-burning fireplaces, even if reinterpreted in contemporary materials. And the numbers of these buyers is growing. According to Dexter Guerrieri, the president of Vandenberg, the Townhouse Experts, 15 of the 48 townhouses sold last year on the Upper West Side were multifamily dwellings being returned to single-family homes, either by developers or what are called "end users." "That's nearly a third of West Side sales," Mr. Guerrieri said, "a high percentage and one that's been increasing in recent years." He and other townhouse watchers attribute the shift in part to a desire for bigger and more opulent homes that provide a degree of privacy unavailable in condominiums and especially co-ops. These homes also often offer other benefits: Residents can have a garden; they can own a dog without asking anyone's permission. Many of these houses are in picturesque neighborhoods with an embracing sense of community. "But money is the driving force," Mr. Guerrieri said. Values are rising, and developers are seeing the big numbers that these houses sell for. An earlier version of this story misstated the price of a townhouse on West 90th Street. It is $12.995 million, not $14 million. The error was repeated in a picture caption.