The forthcoming 10-story addition to 711 West End Avenue will be one of the most interesting projects to watch, not because of a high-end design team or super expensive condos, but because of how it's going to be built. The addition technically won't be an addition. A website for the project explained that the new section will kind of hover above the existing structure, and now the Times explains "it would essentially sit not atop the old building, but above it, with its bottom floor hovering more than 80 feet in the air." Here's how:

a steel and concrete platform supported by a crisscrossing steel superstructure surrounding but not touching the lower building. Other than the shaft for a new elevator and fire stairs that will run from the lobby to the new eighth floor, the buildings are totally separate. A roughly six-foot gap will separate the roof of the existing 1952 building and the bottom of the new one because they must comply with different fire codes, though the facade of the Art Deco-inspired addition will obscure the gap. The idea is to unify the buildings visually but not physically.Sounds neat, but why do this at all? Here, the top 10 floors will sit onsupported by a crisscrossing steel superstructurethe lower building. Other than the shaft for a new elevator and fire stairs that will run from the lobby to the new eighth floor, the buildings are totally separate. A roughlywill separate the roof of the existing 1952 building and the bottom of the new one because they must comply with different fire codes, though the facade of the Art Deco-inspired addition will obscure the gap. The idea is to unify the buildings visually but not physically.Sounds neat, but why do this at all?

The existing seven-story building, which stretches between 94th and 95th Streets, holds 144 apartments, the majority of which are rent-stabilized. This means that demolishing the building to make way for a new one would be hard (it's unclear why a conventional addition could not be built, but it's likely because the existing structure would not support it, but the Times doesn't go into this), and developer Paul Boardman wanted to go bigger without displacing current tenants.

This hover-addition allows that to happen, though there will certainly be quite a few disruptions for residents, many of whom are very concerned about the development. Boardman is developing the building with the Miller family, the owners of 711 West End Avenue, and SJP Properties, a New Jersey-based developer. Some of the Millers and Boardman's relatives live in the building, and the developer says this should be reason for the tenants to believe that they have their best interests in mind. The team will also be upgrading the rentals with air-conditioning and new windows. A new lobby will be constructed, along with a shared courtyard garden,

But tenants, many who have lived in the building for decades, remain suspicious. One 52-year resident said, "This isn't for the tenants; it's for them. They just want it to look nicer so they can sell their condos."

· When Tenants Can't Be Evicted, Building Around or Over Them [NYT]

· All 711 West End Avenue coverage [Curbed]