Sometimes, squeaking floors are symptoms of structural weakness: cracked or sagging headers or joists; rotting posts, beams or joists; joists weakened by plumbing notches; missing or non-existent blocking or bridging between joists; and so on. While you can eliminate the squeak without fixing the cause, it’s a good idea to check out the extent of the problem under your floor, and reinforce or replace any weak sections.
For common, but less serious problems, here are some remedies.
Squeaks are caused by moving floorboards or subfloors, which rub against each other or on their nails. You can secure floorboards to the subfloor by screwing from below. Drill a pilot hole through the subfloor, dip a screw in glue, and drive it tightly. Try not to walk on that area of the floor for 24 hours.
If you find one joist has separated slightly from the subfloor, causing bouncing when you walk on the floor, drive a shim between the joist and the subfloor.
If you can’t work from underneath, try these tricks.
A popped floorboard with a broken tongue or groove can be reinstalled with carpenter’s glue. Squeeze glue into the crack with a syringe, or pour a tiny amount of water into the crack first. Then weigh down the board.
For fast relief, pour powdered graphite between squeaking boards to lubricate the squeak, and add as necessary.
You can also drive metal glazier’s points as shims between squeaking boards. Use a nail set to get them below the floor. (You may want to paint them black so they’re less apparent.)