First, find the source of the squeak
Floor squeaks are caused by wood rubbing against a nail, other wood, or even ductwork and piping. Finding the squeak can be difficult, but if the squeaking floor is open from below, you’re in luck. You’ll have several options to stop it.
To locate the source of the squeak, have a helper spring up and down on the squeaky area while you listen and watch for subfloor movement from below. Also look for loose nails or subfloor seams rubbing against each other. It doesn’t take much movement to cause a squeak, especially since your floor amplifies the sound like a giant soundboard.
If you’re working alone, measure the squeak’s location in relation to a wall or heating register that you can locate from below. Then go downstairs and measure these distances along the subfloor. Or, if your floor is carpeted, you can drive an 8d finish nail through it to mark the squeak source.
Fill gaps with shims
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Photo 1: Shim between the joist and subfloor
Slide a pair of shims into the gap for a snug fit. Draw a line on each shim to mark the depth. Don’t wedge the gap wider.
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Photo 2: Glue the shims
Add a bead of construction adhesive to both sides of each shim. Shove shims back into the gap. Align to the depth line.
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Photo 3: Trim the shims
Score the excess shim two or three times with a sharp utility knife and snap it off. Keep off the floor for four hours while the adhesive hardens.
Finding the exact cause of the squeak, and then choosing the best remedy, isn’t always a simple task. Don’t be surprised if you have to try several solutions before you stop it for good. Look for gaps between a joist and the subfloor first. Plug in a drop light and examine the area closely; a gap or movement may not be obvious.
If you spot a gap, use the wood shim solution to stop floor movement. Shims are available at any home center or lumberyard. Push a pair of shims in lightly. If you drive them in, you’ll widen the gap and potentially create a new squeak. Adding construction adhesive before final assembly makes the fix permanent while filling in irregularities between the wood surfaces.
Reinforce the joists
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Photo 1: Measure the gap
Measure the length of the subfloor gap for 2x4 blocking. Extend the block about 1 ft. on each end. Cut away protruding nails with diagonal cutters.
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Photo 2: Add a 2x4
Predrill 3/16-in. clearance holes every 12 in. along the 2x4 at a slightly upward angle for the screws. Then apply construction adhesive liberally to the top and the side of block, press tightly to the subfloor and drive 2-1/2 in. wood screws into the joist.
If you spot wide gaps along sagging or damaged joists or see that a subfloor edge is poorly supported, add blocking to support the subfloor and stop movement. Also keep an eye out for protruding nails and clip them with diagonal cutters. (You may need a strong grip and a few tries to work your way through the nail!)
Measure and cut a 2x4 block that’s 2 ft. longer than the poorly supported area. Apply construction adhesive to the side and top of the blocking before installation to add strength. It should squish out when you screw the 2x4 in place. Predrill screw holes (for 2-1/2-in. wood screws) to prevent splitting the block and to make driving easier.
Construction adhesive contains a strong solvent. Wear a respirator with an organic vapor cartridge when working in closely confined areas.
Fill gaps with construction adhesive
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Force adhesive into the gaps
Squeeze a thick bead of construction adhesive into the crack along both sides of the squeaky joist and subfloor. Apply adhesive to adjacent joist/ subfloor joints as well.
Sometimes the gapping between the subfloor and joist is too narrow, too irregular or too widespread for shims to be effective. Or perhaps you can’t pinpoint the exact source of the squeak. A good solution is to use a bead of construction adhesive to glue the wood together. You don’t have to press the gaps closed; construction adhesive fills the space and hardens. The key is to force it as far as possible into the gaps without widening them. Work both sides of the joist for a strong, lasting connection. And glue nearby joists as well in case you can’t find the exact squeak source. Keep off the floor for a day until the glue hardens.
Block beneath squeaky joints
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Photo 1: Insert the block
Cut 2x8 blocking to fit snugly between joists. Add construction adhesive to the top and slide it into place.
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Photo 2: Screw the block
Predrill angled pilot holes with a 1/8-in. bit. Drive 3-in. wood screws to force the block snug against the subfloor seam. Drive an additional pair of screws (or 16d nails) through the joist into the block on each end.
Once in a while, movement in a subfloor joint will cause a squeak. You can stop it by screwing and gluing 2x8 blocking under the joint to give it solid support. First angle-screw through the blocking, up into the joists, to ensure a tight fit. But be sure to drive additional nails or screws to anchor the block. Otherwise it might work loose and cause more squeaks!
Screw hardwood flooring from below
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Screw from below
Mark the depth of the pilot hole on a 1/8-in. drill bit with tape. The depth should be 1/2 in. less than the floor thickness. Drill pilot holes 4 to 8 in. apart. Drive No. 8 wood screws flush to subfloor.
A solid wood floor is usually fastened with hundreds of nails, so squeaks often occur as the floor ages. But some squeaks aren’t caused by nails; they come from one edge of a board rubbing on another. A simple “first” solution is to dust the squeaky area of your floor with talcum powder, working it into the cracks. The talc reduces friction and may solve the problem, at least for one season.
Note: Talc can be slippery. Wipe off the excess.
For a more permanent solution, however, you’ll usually have to screw the subfloor to the wood flooring from below. Drill a 1/8-in. pilot hole about 1/2 in. less than the thickness of the entire floor, and buy screws 1/4 in. shorter than the floor thickness so they won’t penetrate the surface. You can find your floor thickness by either removing a floor register and measuring the floor where the duct comes through, or by drilling a small hole in an out-of-the-way corner and measuring with a nail.
To maintain a safe margin, mark the desired drilling depth on the drill bit with masking tape. Space your screws about every 6 in. in the area of the squeak. Have someone stand on the floor above while you drive the screws. Set the heads flush with the subfloor. Sinking the head into the subfloor could cause the screw point to break through the finished floor surface.