While Mies preferred an open plan for the apartments, developer constraints resulted in a plan with separate rooms. As originally built, there are four 6-room apartments per floor in the 860 building. The apartments in the 880 building are approximately one-half the size of those in the 860 building resulting in eight 3 and 1/2 room apartments per floor as originally built. Over the years many apartments have been combined to create larger apartments or modified to Mies’ preferred open plan.
The illustration below was extracted from the 1957 brochure The Glass House, 860-880 Lake Shore Drive, A Home for Gracious Living.