A floor that bounces as you walk across it may just need to be stiffened with bridging, which spreads the load on each joist to adjoining joists, strengthening the whole floor.
If the china cabinet in the next room rattles as you walk across the floor, try stiffening that floor fast with inexpensive metal braces called “bridging.” Bridging allows each joist to share weight with its neighbors and can cut “deflection”—how much the joists flex—by half. Even if your floor already has a row of bridging running down the center, you can stiffen it substantially by adding two more rows. The catch, of course, is that the bouncy floor joists must be accessible from below.
Start by making sure the original bridging is tightly fastened; add nails or screws if necessary. Then measure the span of the joists (the distance between walls or beams that support the joists). Divide the span by three and add rows of bridging at both of the one-third points. The joists shown here, for example, span 12 ft., so we added rows of bridging 4 ft. from both ends of the span.
Various types of metal bridging are available at home centers and lumberyards. To install the type shown here, drive the toothed end into the joist and nail the other end. Adding two rows of bridging costs a few dollars per joist. Other versions are just as easy to install and inexpensive. Measure the joist spacing before you go shopping; bridging is sized for joists centered 16 in. or 24 in. apart. Don’t add bridging to manufactured lumber like I-joists or truss joists until you consult an engineer or building inspector.