How to Fix a Squeaky Floor Caused by Gaps between the Subfloor and Finished Floor
Squeaky floors can be extremely irritating. Fixing a squeaky floor caused by gaps between the subfloor and the finished floor is easiest if you have a basement or an access space.
Floors get squeaky when wood dries out (either finished wood or a wooden subfloor), causing the subfloor nails to pop loose and the subfloor to separate from the finished floorboards.
Gather your materials: Chalk, screws, screwdriver or electric drill.
You also need a helper who weighs enough to make the floor squeak. A pipsqueak of a kid may not weigh enough to create a squeak.
Have your helper walk across the floor looking for squeaks. Mark the spot with chalk.
Go to the basement under the room where the floor squeaks. Have your helper walk across the floor and stop when they hear the squeaking. Your helper may have to bounce up and down a couple times until you identify the exact location from below.
Screw the subfloor to the underside of the finished floor.
If you don't see any gaps, screw the subfloor to the underside of the finished floor to stabilize it.