A young Manhattanite sold her West Chelsea townhouse and used the proceeds to buy a ground-up townhouse in Crown Heights for a record-breaking $3.45 million in a deal that closed this month.

The seven-bedroom, 71/2-bathroom home, located at 832 Dean St., is 5,400 square feet.

It’s now configured as a three-family building, with a lower garden duplex, a middle simplex and an upper duplex with a private roof deck.

The property has wide-plank walnut flooring throughout, marble baths and high ceilings.

Douglas Elliman listing broker Alex Maroni declined comment.

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