Noah Fecks East 10th Street. The second building from the right was approved for a rooftop addition only hours before the street was designated a landmark district.

The Landmarks Preservation Commission approved a historic district on a block of East 10th Street along Tompkins Square Park today, though a controversial rooftop addition that led to the expedited hearing also got the go-ahead literally hours before the vote.

With the designation, the exteriors of the 26 buildings between Avenues A and B will essentially be preserved as-is. But at the meeting the executive director of the Greenwich Village Society for Historic Preservation, Andrew Berman, revealed that developer Ben Shaoul’s plans for a rooftop addition to 315 East 10th Street had been approved by the Department of Buildings.

“It reflects poorly on Shaoul and the city agencies that they couldn’t get their act together,” said Mr. Berman.

Robert Tierney, the chair of the Commission, later confirmed that the addition had been approved. “A building on this magnificent row is under threat with a potentially unsympathetic — to put it euphemistically — rooftop alteration,” said Mr. Tierney, who called the expedited hearing “highly unusual.”

The news marred what was otherwise a landslide victory for local preservationists. The Commission voted unanimously to approve the small district — the first one in the neighborhood since 1969 — and none of the roughly 20 speakers at the public hearing at 1 Centre Street spoke in opposition to the designation.

“This is one, if not the most significant block-fronts in the East Village,” said Richard Moses, the president of the Lower East Side Preservation Initiative. “Its commanding presence at the north end of Tompkins Square Park provides a wonderful iconic view from within the park.”

Stephen Rex Brown The Commission, moments before the hearing began.

Mr. Shaoul has not yet responded to a request for comment, and the nature of the rooftop addition is unclear. Previously, Mr. Shaoul told The Local that the addition would not be visible from the street, making it not subject to approval from the Commission. A spokeswoman for Commission said that it had been in contact with a lawyer for Mr. Shaoul. “His client plans to meet with us to discuss suggestions for the design of the one-story addition and is willing to work with L.P.C. staff as they move ahead on their grandfathered permit,” the spokeswoman said.

Still, some were not as optimistic during the meeting.

“When in doubt, act,” said Mr. Tierney, exhorting his fellow commissioners to vote to approve the district in light of the rooftop addition.

As for the approval by the Department of Buildings, Mr. Tierney had little explanation for the apparent lack of coordination between the two agencies. “They’re required to adhere to their own regulatory time frames,” he said of the Department of Buildings. “They usually work in sympathy, but there are rare cases like this one.”

A date for the public hearing on a much larger — and more controversial — historic district centered on Second Avenue has yet to be set.

Update | 5:39 p.m. Added comment from Commission spokeswoman and corrected spelling of Robert Tierney’s surname.