Floors are meant to be sturdy, so any bounce in the floor structure while walking over it may be disconcerting. A bad bounce can cause pieces to fall off shelves and bookcases to shake. Bouncy floors are commonly caused by the floorboards or the subfloor coming loose from the joists they're installed on. Warped joists or floor can also cause bouncing. Luckily, a bounce does not mean you need to replace the flooring. There are a few cheap solutions.
Inspect the floor joists underneath the bouncing floor and look for loose screws. Tighten the screws for the floorboards to see if the loose screws are the problem.
Measure the length and width of the floor joist area and multiply the two figures to get the area in square feet. Use this figure to order plywood.
Hold the plywood up to the underside of the joists, with the long side of the plywood sheet parallel to the joists; attach the plywood using 3.8 cm (1 1/2 inch) masonry screws, one every 10 cm (4 inches). Fit the plywood along the entire floor joist area.
Measure the width between the joists. Use the measurement to order metal bridging at the hardware store.
Place the metal bridging between the joists so that it forms an x-shape. Place two metal bridges between each set of joists, at the one-third and two-thirds points along the length of the boards. Place another one at the midpoint of each joist if there is not a centre brace already installed.
Attach the metal bridging, or bracing, using 3.5 cm (1 3/8 inch) joist hanger nails, two at each end of the brace.
Only use the plywood method if there are no pipes or electrical lines along the joists.