Since the Sears Tower in Chicago's Loop lost its title as the world's tallest building a decade ago, big skyscraper proposals have popped up periodically with the promise of winning back the honor. All have foundered for lack of financing, developer resolve or political support. Now, an Irish developer with little high-rise experience is poised to start construction on a condo tower that will puncture the city's skyline.

The Chicago Spire is planned to rise 150 stories at a projected cost of $1.2 billion or more. It's unusual on several counts. The developer, Garrett Kelleher, head of Shelbourne Development Ltd. in Dublin, has made a living mostly erecting residential buildings in the Irish capital, where the tallest edifice is merely a mid-rise of 15 stories.

Chicago is renowned for its architects, but Kelleher enlisted Spanish designer Santiago Calatraya, based in Zurich, and a veteran of projects like the birdlike addition to the Milwaukee Art Museum. The goal: to create an eye-popping twisted spiral design that some local pundits have dubbed the “Twizzler Tower.”

Kelleher intends to build on a site a block from Lake Michigan, in a residential neighborhood. The Spire is planned to be all condos, about 1,300 units spread over 2.5 million sq. ft. Marketing hasn't begun yet, but the developer has hinted that prices will almost certainly exceed $1,200 per sq. ft. — the current top of the market in Chicago — and possibly go much higher.

There are plenty of skeptics who doubt there is much demand for such expensive residences in the city. Donald Trump, whose own luxury condominium-hotel tower is under construction nearby along the Chicago River, has called the Spire “financial suicide.”

Nevertheless, the 45-year-old Kelleher is moving ahead. He plans to appear before the city council in late spring to get approval for his plans, and then begin construction later this year, with completion slated for 2010. Financing, he says, is already arranged. Kelleher's personal net worth is estimated at $750 million, and he will bring considerable equity of his own to the project, with the Anglo Irish Bank providing financing.

“There are no other investors in this project and no mezzanine debt,” Kelleher said in a presentation to a local architectural society in March. “It's just Garrett Kelleher and the Anglo Irish Bank.”

Kelleher says he'll break ground with no condo pre-sales at all. “When this building launches, the news will appear on front pages around the world,” the developer proclaimed. Noting that the Spire will have views of both Lake Michigan, the shopping mecca of Michigan Avenue and the river and downtown business district, Kelleher insists that “this is the best site that's ever become available in Chicago.”

Neighbors, concerned mostly about the new traffic on the quiet residential streets of the surrounding Streeterville community, have watched the high-rise planning warily. “Kelleher doesn't seem to have much experience in this kind of construction, but he's assembled a world-class team of architects and engineers and that relieves some of the anxiety we have,” says Gail Spreen, who heads a local residents watchdog group.

Though 2,000 feet high, the Spire is not likely to claim the world title when it's complete. The Burj Dubai under construction in the United Arab Emirates capital is slated to reach 2,300 feet when it's completed in two years. “Even if the Spire is not the tallest building in the world, we think it will be the most beautiful,” concludes Thomas Murphy, legal counsel to the project in Chicago.