Traditionally, developers looking to turn rent-regulated apartment buildings into condos have had two options: try to buy the tenants out, or wait a long, long time for all units to become de-regulated. The owner/developer at 711 West End Avenue, between 94th and 95th streets on the Upper West Side, is planning to build a condo building atop an existing rent-regulated apartment building. The plan is not simply to add floors, which is notoriously difficult in an occupied building. Instead, the ten newly constructed condo floors will essentially “float” six feet above the existing six-story building, carried entirely by support columns. With the exception of a common elevator shaft and fire escape staircases, the two structures will be entirely separate. The existing tenants are naturally trying to challenge the project that the Department of Buildings approved in June. The developers argue that the new structure will benefit the rent-regulated tenants, in part because the construction will add central air conditioning, a new lobby and a courtyard garden.