The current roof work is being done under Landmarks Preservation specifications, said the employee.
The employee would not say when work would be complete, but she said work was on schedule. A work permit from the Department of Buildings posted at the entrance of the building expires January 1.
The work is being done because the current terra cotta pillars were deteriorating and causing leaks, she said.
The roof garden, which is closed during the estimated $1.5 million construction work, will reopen before all the pillars are replaced.