We're turning a 13x13 area of attic space into livable space. The new 13x13 area joins an existing room. The attic floor structure is: 2x8 floor joists and OSB board on top.
There is a ~5 inch step down from the current room into the attic space area. Someone presented the idea of keeping the OSB board on top of the 2x8 joists and running 2x4 joists on top of the OSB board. The 2x4s would run opposite of the 2x8's and the OSB would be sandwiched in between the existing 2x8s and the new 2x4's. On top of the 2x4's, we would place two layers of plywood to bring it flush with the existing room.
Should the OSB be removed first?