A A mezzanine floor is a semi-permanent structure built within a building to include an upper ground floor or several floor levels. The existing base is central to the roof and ground floor, providing a new amount of available space without compromising the building's main structure. The foundation of the mezzanine constitutions is a network of vertical steel columns that support the decking above. Since partitions do not bound the upper level, you can see the ground floor from the mezzanine deck, and uncovered edges are rendered transparent with handrails and infills. Although a mezzanine floor.