Over the course of time, most wood floors develop squeaks. Changes in temperature and humidity cause different parts of the floor to swell or shrink at different rates, resulting in boards that rub against each other or against loose nails. The first step is to locate where the squeak is coming from. If company's coming and you need a quick fix, a little graphite or talcum powder pressed between the boards usually works. To stop the squeak permanently, you have two options. If you have access to the floor from below, go down and watch what happens when someone walks on the noisy spot. If the problem is a loose board on the subfloor, it can be fixed by dipping a shim in glue, then tapping it between the joist and subfloor until it's snug. To secure loose joists, install steel bridging between them, or make solid bridging from the same wood as the joists. You can also use one-and-a-quarter inch roundhead screws to pull loose finish boards back into place. Weight down the upper side, drill pilot holes, and use washers to keep the screws from pulling through the subfloor. If you can't get to the floor from below, you'll have to quiet the squeaks from above. Find the loose board and drill diagonal pilot holes into the subflooring. If possible, try to drill into a joist, as well. Nail the board back in place using galvanized finishing nails. Don't use smooth ones, which may pull loose. Countersink the nails with a nail set and fill the holes with wood putty. When it's dry, sand the surface smooth.
