I have a lounge floor, 16 X 12 feet wide, which has 5" X 2" joists at
11" centres along the width (12 feet). I have removed a toilet and pantry underneath, the walls of which helped to support the floor in question. The floor is ok but a bit bouncy, since it should really have 7" joists. I intend to put a 16 foot RSJ underneath at 7 feet along the width. Any help in calculating the size of the RSJ? How thin can get away with, bearing in mind that anything would improve the situation? Hope all this makes sense! Any help greatly appreciated!