From brand new homes to century old mansions squeaky floors have been around forever. There are countless methods and materials available to eliminate these squeaks, but none better than what I will share with you today.
Get yourself a few tubes of quality construction adhesive, (liquid nails is my favorite), a bundle of narrow shims, a step ladder, hammer and a drop cloth or old blanket. As time passes the wood will shrink and/or the adhesive will dry out causing gaps between the floor components. The squeaking comes from movement of these gaps, either wood on wood or wood on a nail. Eliminate the movement, eliminate the squeak…
This technique requires two people and access to the underside of the floor. Get your stepladder in the area of the squeaks and have your partner walk around the room you are working on. How to say this delicately…. You need a heavier person walking on the floor, in this case the more the better.
In prepping the area it is best to put down an old blanket or drop cloth so when you drop some glue it will not damage the floor; and you will drop some.
What you are looking for is movement between the plywood flooring and the floor joists (the long narrow pieces of lumber that support the plywood). Once you have located the area that the noise is coming from take the narrow end of the shim and try to slide it between the plywood and the top of the joist. Don’t be fooled thinking it won’t fit, the angle you will be looking from can be deceiving. When you have found an area that you can get a shim in pull it out and with your caulk gun squeeze as much adhesive into the space and (don’t be stingy) put some more on the end of the shim and slip it back into the gap you identified earlier, tapping the end of the ship with a hammer. Look at the other side of the joist and see where the shim came out, to make sure there is glue on the end of the shim. If not use more adhesive next time. Continue working in either direction from the first shim as it may open up the gap a tiny bit. Have the person upstairs walk over the spot, and if the squeak is gone, move to the next spot. Avoid excessive walking until the adhesive has had a chance to dry. Use as many shims as necessary and fill all the gaps, and remember liberal amounts of adhesive is the key.