In a unanimous vote last evening, the Whitney Museum of American Arts 45-member board of trustees approved the cramped museum's plan to build a new six-story Renzo Piano-designed building downtown, in sight of the trendy High Line and in the thick of the youth-friendly Meatpacking District.Groundbreaking on the city-owned site is expected to take place in May of next year, and the museum is projected to open to the public in 2015.

The green light for completing the massive $680-million project leaves open a range of possibilities for the Whitney's Marcel Breuer-designed building on Madison Avenue, a Brutalist landmark plunked down in a decidedly well-heeled neighborhood that has defied any move for significant infrastructural change since opening in 1966.The most intriguing of these, as ARTINFO reported last Thursday, is the option that the museum may lease the building to the Metropolitan Museum of Art once the Whitney’s new site is ready for occupancy. While the long-secret talks regarding the potential arrangement are still underway, curators in several of the Met's departments have begun sketching out shows that could be produced off campus, since even the Fifth Avenue encyclopedic museum's massive exhibition space has been outgrown.

“Met curators are having a food fight about who is going to get more space and where,” according to a source close to both museums. Met staffers view leasing the Whitney, with its 32,000 square feet of gallery space, “as a once in a lifetime chance to get more space,” the source says. If the arrangement is approved, it would be the most seismic museum news in New York since the Museum of Modern Art merged with P.S.1 Contemporary Art Center in 2000.

Whitney board chairman Leonard Lauder, who gave the museum it's largest-ever donation with the gift of $131 million in 2008, has been opposed to the museum selling its Madison Avenue flagship building. But according to a front-page New York Times article about the discussions with the Met — which were first reported here — Lauder met with Philippe de Montebello in the summer of 2008 to discuss a possible alliance. A source tells ARTINFO that a New York collector who supports both museums also wrote to de Montebello that year to advocate for the partnership, but that the museum eminence replied that while it was an excellent idea, it was a matter for his successor, Thomas Campbell, to pursue. Reached for comment, de Montebello replied by email that he has a "self-imposed ban on opining on what the Met is or may be doing."

According to a museum trustee who was present at the Whitney meeting yesterday, no one expected Lauder to vote in favor of the downtown expansion, resulting in an emotional scene when he cast his "aye." The trustee says that the Met plan was not discussed in detail during the meeting, with those present unwilling to bring up a second sensitive topic in Lauder's presence, given his passion for the Breuer building. A spokesperson for Lauder declined to comment on the potential Met plan, but relayed a statement from the cosmetics magnate regarding the approval of the High Line site: “The stars are all aligned now. This is the right time to build, the right time to finance, in the right neighborhood, with the right board. Nothing could be better.”

As for the value of the discussed lease, one real-estate expert estimated that the Breuer building — too august a structure to be torn down for a high-rise luxury apartment — could realistically command a $400-per-square-foot price on the market, potentially representing a $34 million windfall for the museum. The Whitney can also profit from intended sales of the surrounding brownstones it owns, as well as its unremarkable Richard Gluckman-designed 1998 addition, which isexpected to bring another $100 million.

Should the Whitney depart Madison Avenue entirely for the downtown space, it would not be unprecedented, given that the museum has already moved twice in its 80-year history, first in 1954 from its location on West Eight Street (now the home of the New York Studio School), where Gertrude Vanderbilt Whitney founded it, to a site on West 54th Street behind MoMA, and then to its distinctive but too-small surroundings today.