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A wealthy real-estate investor paid nearly $8 million for a 19th-century rowhouse on one of Manhattan’s historic blocks. It already had four floors of living space, but he wanted to make it even bigger and add an elevator and other modern luxuries, leaving little intact behind the red brick facade.

His plan set off the latest battle over the character of some of New York City’s most expensive neighborhoods, pitting affluent buyers who believe they have every right to remake the urban landscape, just as others have done for generations, against preservationists who contend that things have gone too far.

In Chelsea, where the rowhouse sits, residents banded together in protest, fearing that they were being targeted by a wave of speculation that would turn some of the oldest houses in the city into much larger, modern mansions for wealthy interlopers.

They had already lost one fight.

A local community board had tried in vain to stop a similar expansion just seven doors away, in a home that is considered the oldest dwelling in Chelsea.