I live in a four-year-old ranch with a full basement. A loud and worsening squeak has developed in the middle of the master-bathroom floor. The floor is tiled, and the basement ceiling is drywall. I plan to remove a section of drywall to access the bottom side of the floor, but how should I fix the squeak?
— Tony Blair, Belmont, Maine

Squeaks are often the result of movement of the subfloor sheathing around a nail, but they also may be caused by loose joist blocking or other wood-to-wood or wood-to-pipe movement. This can happen as framing dries out and spaces develop or fasteners loosen.

Pinpointing the squeak is always a challenge. After you’ve removed the drywall from the bottom of the joists, you can have someone walk on the floor above while you try to locate the precise spot where the noise is coming from. Then you have to fill any gaps, even tiny ones, where the two components making the noise come into contact. I’ve had success applying subfloor adhesive to the joints between joists and blocks or between joists and subfloor sheathing. Try getting the adhesive to flow into larger gaps. You can help it to do so with a knife blade or other thin piece of metal. Finish with a bead of adhesive along both sides of the joint. When the adhesive cures, it should stop the movement between the building components.

An alternative to using subfloor adhesive is to apply a small bead of two-part high-density spray foam alongside the components suspected of causing the squeak. So that you can test the effectiveness of the repair, wait a few weeks before reinstalling drywall on the ceiling.