Stairs are made up of treads, which are the part you step on, and risers which are the vertical kick plates and stringers which are the saw-tooth pieces of wood that support the stairs from the sides and from underneath.
Since there are so many pieces of wood used to construct stairs it is inevitable that they will squeak at some point. Age tends to loosen the joints in stairs as the wood continues to dry and with the continual use that flex and strain the individual components. This causes the treads to rub against the risers and stringers and work against the nails and screws that hold it all together. In addition to being walked on, the seasonal contraction and expansion of the wood due to varying humidity levels adds to the loosening of the joints. Stairs that were constructed with glue as well as with nails and screws are less prone to squeaking, but wear and time do tend to take their toll. In older homes stairs may have been constructed on site and may not have been glued at all.
Locating a Squeak
Most of the time problem is relatively simply to fix. The noise doesn't mean your stairs are about to collapse, they just need a little tune up.
If you have access to your stairs from below, you can fasten wood blocks or brackets from underneath. These repairs are good since they are invisible, but not every set of stairs is accessible from the underside and tightening them on the top should solve the problem.
You will need to identify exactly where the squeak is coming from. Most likely, either the tread is knocking or rubbing against the riser board, the tread has come loose from one or more of its stringers, or both may be occurring. Begin by testing each step that squeaks and repair it individually by refastening the tread to the riser or stringer where the squeak occurs.
If a stair squeaks when you step anywhere along the front of the tread you can typically correct the problem by nailing the tread to its riser where they come together. If the stair squeaks in another place, such as along the back or to one side or the other, you will need to secure it to the stringers. Most stairs have three stringers, one on each side and at least one running down the middle. Wider stairs may have more than three stringers. Each of the stringers is a 1 ½ to 2 inches thick.
Repairing a Squeak
Since repairing a squeak involving stringers is slightly more complicated, the steps for this type of repair will be given in more detail.
You should be able to tell where the stringers are by the position of the existing fasteners, or by looking underneath if you happen to have access to the underside of the stairs. If you are unable to tell by these methods, you can try tapping the treads lightly with a hammer and listen for a thud instead of a more hollow sound. Start on one end where you know there is a stringer to pick up the change in pitch. Once you’ve found the location of the stringers and the one that needs repairing you can begin your repairs. It is best if you can have someone help you with this repair and you’ll want to have your helper stand on the stair with one foot on either side of the stringer to help press the thread to the stringer. Carefully drill two pilot holes into the tread at opposite 45-degree angles. You don't need to drill all the way into the stringer below. Use 8- or 10-penny finish nails for this repair and the holes should be slightly smaller than the diameter of the nails. You then drive the nails through your holes into the stringer, setting them a little bit below the surface of the tread. You can then cover the holes with some wood putty. If you can find ring-shank or glue-coated nails, these may hole better than smooth finish nails, but the purpose of nailing them in at opposite 45-degree angles is to lock them into place.
A nail driven straight down will work itself loose over a period of time with the movement and bounce in the stairs.
Carpeting needs to be removed before you can fix the stairs. If the stairs are fully carpeted you may want to screw your riser boards into the stringers to tighten everything up. Typically carpeted stairs are constructed out of pine and are not meant to be left exposed. More elaborate stairs will have pine or poplar stringers and risers and oak for the treads. The best way to do this is to drill a hole into the top of the tread with a countersinking bit. This bit has the profile of a wood screw. You can then use 1 ½ to 2 inch screws to secure the riser to the tread and then use a plug or wood putty to fill the holes. You can also add a few drops of wood glue into the hole before the screw.
Screwing a Tread and Plugging the hole
For repairing a squeak along the front edge of the tread you should drill a pilot hole about three-quarters of the way through the tread and then nail the tread into the riser with 8-penny finish nails.
A less common source of squeaks are loose moldings on the underside of the tread nosing. Typically cove molding is installed under the tread to cover the gap between the riser and tread. Small finish nails may be rubbing against the riser and tread making a high-pitched squeak. Remove the molding with a small flat bar and reinstall it with 4-penny nails in different locations. If you can see the nail causing the noise, you may be able to repair it with a pair of needle-nose pliers or pry off the trim slightly and pull out the nail.
A silent set of stairs is a must for any home and with these simple repairs you can achieve this goal on your own.