Reinforce Floor Joists With Steel Plate
You will have to use a very sturdy piece of wood or some steel plating to reinforce the floor joists.
Reinforce floor joists with steel plate. A special countersunk 2 hole design allows flat head screws to sit flush with the material. A steel plate can be used the same way. Measure the width between the span of two joists. Made from 14 gauge steel the notch reinforcer can be used to patch a notch up to 5 inches wide and 3 inches deep custom plates can be engineered to reinforce larger gaps.
Place the lumber block between the two joists. The everbilt 2 in. Cut a piece of 2 by 6 or 2 by 8 lumber according to the width. Screw the metal joist to the existing wood ceiling joist and to each plate and you have very effectively reduced the load deflection of any stored attic loads for little cost.
Either way you can reinforce each joist or specific joists by doubling or tripling them. Steel is so much easier to work with and weighs. Floors bounce because the joists are either too small or they span too far. The solution is simple sister on an 18 gauge 1 5 8 x6 steel stud material to act as a joist running plate to plate.
Nail the block in place with 16d. Mending plates 4 pack are the ideal reinforcements for flat surface joints seams or cracks. Mending plates 4 pack are the everbilt 2 in.