Philippe Starck is throwing a couple of curves on the Corner.

He is helping design the conversion of 15 Broad Street into a condominium called Downtown by Philippe Starck. The 42-story apartment building will have an aerial front yard on the rooftop of the five-story 23 Wall Street, which it embraces on two sides, overlooking the New York Stock Exchange and Federal Hall National Memorial.

Is that a spinning sound you hear as Mr. Starck holds a chandelier crystal to his head like an earring? It may be coming from the graves of old-time bankers who knew 23 Wall Street as the House of Morgan, 15 Broad Street as the Equitable Trust Company and the intersection of Broad and Wall as the Corner - epicenter of American finance.

“It is fantastique to have a garden here,” Mr. Starck said on a recent visit to the 5,000-square-foot rooftop. He envisions trees and teak decking, surrounded by a topiary wall with windowlike openings in which lanterns will hang. A large pool will be fed by a tall, crook-shaped pipe, looking like a giant faucet.

That is a departure for a place where roll-top desks were standard issue until 1963.

Twenty-three Wall Street was built in 1914 and linked in 1957 to 15 Broad Street. The buildings were later remodeled as headquarters of the Morgan Guaranty Trust Company, corporate forerunner of J. P. Morgan Chase & Company. In 1998, a deal was reached under which every building on the block - except for 23 Wall, an official landmark - was to be razed to make way for a new stock exchange and office tower.

That project fell through after the attack on New York. Last year, A. I. & Boymelgreen of Brooklyn bought the Morgan buildings for $100 million. It is spending about $135 million on the renovation, said Shaya Boymelgreen, the president.

Ismael Leyva of New York is the project architect working with Mr. Starck on the conversion, which is to be finished next year. Prices for the 326 units will range from about $335,000 for a studio to $3.5 million for a three-bedroom apartment.

Despite residential conversions all around, the Corner is still strongly financial. Barricaded behind truck blockades and patrolled by heavily armed police officers, the intersection may not be everyone’s idea of a prime residential address.

But Boymelgreen has guaranteed attention for its project by commissioning Mr. Starck, 55, arguably France’s best-known designer, who had a large hand in recreating the Royalton, Paramount and Hudson Hotels in Manhattan.

“Philippe is bringing humanity to the project,” said Asi Cymbal, vice president and general counsel of A. I. & Boymelgreen. And a knack for raising eyebrows.

“It will be the first fertile place on Wall Street,” Mr. Starck said, peopled by families and children; a “paradise island” with its own bowling alley, basketball and squash courts, lap pool and small theater. It will, he said, embody “honesty, respect, tenderness, surrealism, poetry, surprise, vision - which have no value on the other side of the street.”

Speaking of which, what about that wartime security outside? Predicting a big change in foreign policy after the election, Mr. Starck answered: “All that will become quiet. Today, it’s impossible to find the solution because you don’t have the right people.”

Mr. Boymelgreen put the police presence in a more upbeat light. “This is the most secure place in the city,” he said. “I can send my wife and children here 24 hours a day.”

A sales office is to open at 23 Wall in six weeks. Eventually, the landmark may be separated from 15 Broad Street and used as a school or hotel. Whatever happens, Mr. Cymbal said, residents will have unimpeded access to the 23 Wall Street rooftop.

Another amenity they will keep is the 1,900-piece Louis XV chandelier that hung in the main banking hall like a glittering, upended elm. Morgan gave the piece to the developers, Mr. Cymbal said, on the condition that it be displayed publicly.

It is to be installed in the Broad Street lobby, hovering inches off the floor, with plasma screens displaying residents’ faces interspersed among the crystals. When he learned on his visit that many pieces had come from Austria-Hungary before World War I, Mr. Starck immediately identified them as Swarovski crystal.

Then, after examining a faceted piece from one of the 250 or so boxes, he pretended to don it as an earring. Moments later, looking over the dull-gold curlicue framework of the chandelier, he instructed a colleague, Mark Davison: “Do it in silver. It will be more magical.”

With that, Mr. Starck galloped out of the basement. As Mr. Boymelgreen hurried after his whirlwind of a designer, he could be heard laughing incredulously. “Philippe,” he said, “every time you come here it costs me another million dollars.”