Q. About 10 years ago, we added hardwood flooring in our second-floor bedrooms. A bad squeak has developed when we walk on one spot in the master bedroom, and we are not sure whether it is the flooring, the subfloor, or something else. I’ve heard that you can use really skinny screws to fix this problem, but I haven’t been able to find them. What do you suggest?
KELLY BEATTY, Chelmsford
A. This is a more common problem than you realize. Often the cause is the wood floor rubbing against the subfloor or other adjacent planks. It could also be the nails moving. The squeaks become more noticeable in the winter when the wood dries out. It’s very difficult to maintain the relative humidity level of a whole house between 40 percent and 60 percent, which is the ideal range for most wood.
If the squeaks are accompanied by gaps, it’s a pretty sure sign that the problem is due to winter dry-out.
If that’s not the case, then most of the remedies require access to the underside of your floor:
■ Shim the squeak
Sometimes the squeak is not in the floorboards, but in the subfloor. One method for solving this problem is to insert a wood shim into the gap between the subfloor and the joist in the area of the squeak. Applying construction adhesive to the seam between the joist and subfloor helps as well.
■ Screw through the joist
Another technique is to apply construction adhesive to the seams where the joist meets the subfloor, and then drive a screw on an angle through the side of the joist into — but not through — the subfloor. Ask someone to stand on that section of floor above you as you drive the screw.
■ Install a ‘sister’ or cross block
If you suspect the squeak is coming from the subfloor and not the floorboards, you may want to install a sistered joist or a perpendicular cross block.
In both situations, apply construction adhesive to one side of the new wood before placing it against the subfloor, and then drive screws through the block and into the joist — but not the subfloor. Then have someone stand on the floor above as you drive two screws through the block — into but not through — the subfloor and into the side of the joist. Tip: Make sure you use the correct-length screws so you don’t come through the finished flooring.
■ Put in a bracket
Install a bracket like “Squeak-Ender.’’ These devices work relatively well and can be adjusted as needed to eliminate a squeak.
If you’re unable to access the squeak from below, you can always try these approaches:
■ Lubricate the floorboards
Pour talcum powder or powdered graphite between the boards, place a cloth over them, and then walk on them to work the lubricant into the cracks. This will reduce the wood-on-wood rubbing between the planks/strips that cause the squeaking.
■ Use the finishing nails
Drive finishing nails through the floor into the subfloor.
Start by pre-drilling pilot holes to prevent the wood from splitting. Start the pilot hole no closer than one-half inch from the edge of the floorboard. Angle the drill slightly toward the center of the board. Make sure that you don’t drill into the subfloor, or the nail won’t hold as well. After the pre-drilling is complete, put downward pressure on the floorboard as you drive the finishing nail into the pilot hole. Use a nail set to countersink the head, and fill the hole with wood filler to match the color of the flooring.
■ Install screws or wood plugs
The use of screws and wood plugs is best done when the flooring will be refinished, to avoid miscoloration.
Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to firstname.lastname@example.org or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.