A. Dan Dolan, P.E., Associate Professor of Wood Engineering at Virginia Tech, responds:A possible solution, which I have used successfully in several cases, is to add a layer of 3/4-inch or thicker OSB over the entire floor, glued and screwed 6 inches on-center in both directions. Make sure the screws are long enough to fully penetrate the new OSB and the underlying subfloor. When possible, using longer screws to penetrate the joists will help some, but the important thing is to make sure the new subfloor is well "clamped" to the existing. Stagger the joints with respect to the joints below. The main problem with this approach is that you gain an inch or more of floor height, which may not be acceptable.
This technique works for one of two reasons, depending on the individual floor. One is that the extra OSB increases the stiffness of the floor, making it vibrate at a higher frequency that is not perceived as annoying by most people (For more on floor vibration, see Practical Engineering, 11/98). In some cases, however, the increased mass of the...
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