What goes up must come down. But when that happens is up in the air when it comes to sidewalk sheds, the ugly steel-and-wood structures that swallow up hundreds of miles of sidewalk space across the city.

Friday night, however, workers will start dismantling the shed that for 11 years has surrounded 280 Broadway, whose tenants include the city Department of Buildings.

"It will be the first time a number of us have seen the building without the shed," said Andrew Rudansky, senior deputy press secretary at the Buildings Department, "including me."

A small portion of the shed will remain up around the New York Sun clock because it was found to have structural issues. The clock will be removed for repairs once a qualified contractor can be found, said Ian Michaels, executive director for public information at the city Department of Design and Construction.

Michaels added the the two-year-long facade restoration project at 280 Broadway cost $17.8 million.

The building is 150 years old and landmarked, and its Tuckahoe marble facade needed repair. The building at the corner of Broadway and Chambers Street is best known for its New York Sun clock. It was once the home of the city's first department store, A.T. Stewart.

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About 300 miles' worth of sheds entomb sidewalks across the city in shadows. The structures go up anytime a building is being renovated or constructed and are necessary to protect pedestrians from falling bricks or masonry. But sometimes landlords decide it's cheaper to rent a shed and leave it there than to pay for costly renovations. So sheds can stick around a long, long time.

One at the corner of West 115th Street and Lenox Avenue in Harlem has stayed in place, with only brief interruptions, since 1990. Another at West 123rd Street and Lenox was finally taken down last year after 14 years. City Councilman Ben Kallos has introduced legislation that would require landlords to take down dormant sheds, but the bill has gone nowhere amid public-safety concerns and opposition from real estate owners.

Gina Gibney, who runs a dance company located in 280 Broadway, said renovation work on the facade began only about two years ago. The shed blocked windows and obscured her company's entrance for a while, which made it harder to rent space for rehearsals, weddings and the other events whose revenue supports her nonprofit.

"This is an incredibly gorgeous building that no one has been able to see for a long time," Gibney said. "I'm so glad its beauty will finally be revealed."