Floorboards creak when two of the planks rub together.
There are several causes of this, but one of the most common is the nails that fix the floorboards to the joists become loose over time.
It’s sometimes possible to solve the problem by pushing talcum powder or chalk between the boards, so try that first.
If it doesn’t work, walk over the floorboards to find out where the movement is. Providing the offending board’s in good condition, you can remove the loose nails and then screw the board back down (using the same holes), which will make it more secure.
Make sure you countersink the screw heads.
If the floorboard isn’t in good condition, this may not be possible, so work out where the joist is – this should be obvious from the row of nails – and drill new pilot holes through the board into the joist. Again, countersink the screws.
If the end of the floorboard isn’t resting on a joist, give it the support it needs by lifting up the board and screwing a 25mm x 50mm batten of wood to the side of the joist. Lay the board on top of the batten and screw back in place.
Never screw or nail into a floorboard unless you know what’s underneath, as this could be dangerous.
Use a battery-operated cable and pipe detector first, although these detectors can be inaccurate if, for example, they pick up the nails in the boards. A more foolproof method is to lift up the board and if you find any cables or pipes underneath, mark them on the surface so you can avoid them.