Bouncy Open-under Staircase
My framer ordered and had installed 3 sets of staircases. Two sets of staircases are supported below with studs while the one which goes from the 2nd to the 3rd floor is not since there is no way to support it. So the staircase is attached to the exterior wall on one side and floats on the other side. We noticed that the stairs are bouncing midway. My framer is MIA now. The staircase installer came by and said that there is nothing much we can do and one option would have been to install a custom-made L-shaped iron, bolted to the wall and running across the stairs (like a L-bracket).
I would appreciate it if someone can shed some light on how to fix the problem. We had to put off drywalling due to this. Attached is a picture of the stairs.