Preparing for growth beyond its proposed new hospital in Chicago’s Streeterville neighborhood, Children’s Memorial Hospital said it paid $18 million Tuesday for a 99-year lease on a building from the Archdiocese of Chicago at 155 E. Superior St.

The six-story building is less than one block from the future site of the Ann & Robert H. Lurie Children’s Hospital of Chicago. That facility, which is scheduled open in 2012 and cost $1 billion, will replace Children’s Memorial’s Lincon Park hospital.