The 5-year project would reduce the tower’s electricity use by 80 percent and save 24 million gallons of water a year, building owners and architects said. Separately, a 50-story, 500-room privately funded luxury hotel with its own green components would be built next to the skyscraper in 3 1/2 to 5 years.

With Thursday’s approval from the Chicago Plan Commission, the design and site plan for the 2,000-foot Chicago Spire goes to the city zoning committee next week.

“This is a wonderful project, and everyone is very enthused,” said Constance Buscemi, spokeswoman for the city’s planning department.

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The city’s planning board has endorsed a proposal for a twisting lakefront tower that would become the nation’s tallest building.

With Thursday’s approval from the Chicago Plan Commission, the design and site plan for the 2,000-foot Chicago Spire goes to the city zoning committee next week.

“This is a wonderful project, and everyone is very enthused,” said Constance Buscemi, spokeswoman for the city’s planning department.

The 150-story tower, which would feature 1,200 residences, would unseat Chicago’s 1,451-foot Sears Tower as the tallest U.S. building. It would also top New York’s 1,776-foot Freedom Tower, under construction at the former World Trade Center site.

The Chicago Spire was designed by Santiago Calatrava, the Spanish-born architect known for designing the Milwaukee Art Museum addition and the Athens Olympic sports complex.

If the zoning panel approves the plan, the City Council will consider it May 9. If it is approved, construction would begin this spring, said Thomas Murphy, general counsel to developer Shelbourne Development Ltd.

Shelbourne executives have declined to estimate the building’s total development cost. Real estate experts put it at well over $1 billion, the Chicago Tribune and Crain’s Chicago Business reported on their Web sites Thursday.