Stairs are both a structural and aesthetic part of the home, and as such, are constructed to hold heavy loads moved across their surfaces many times over. Because of this high amount of traffic over them, most repairs to stairs involve squeaky treads.
A flight of stairs consists of three components: stringers, risers, and treads. The stringer is usually a 2×12 board set at an angle of about 35 degrees. Its bottom rests on the lower floor and its top on the upper floor. A stringer is basically a slanted joist that carries the load on the stair. Typically, a stair that is 3 feet wide will have three stringers, two on either side and one in the middle.
A squeak is often caused by the movement of the step as it is stepped on. It begins to rub against the riser directly below it or at its edge against the stringer. How the squeak is eliminated depends on whether or not the stairs are open from the back. If the back of the stairs are covered with sheetrock or any other surfacing, the repairs must be done from the front.
Have someone stand on the squeaky tread while driving two 8d size finishing nails through the tread into the top of the riser. Nail them in pairs at an angle to each other so that they form a “V”. If the tread is made from a hardwood like oak, drill pilot holes for the finishing nails. Select a drill bit that is slightly smaller than the nail diameter.
Screws are also a means of securing the treads to the risers in the event that nails prove unsuccessful. They may also be your first selection in which case a 3/8″ inch deep hole that allows for the screw-head to be countersunk into the tread. Once the screws have been securely tightened, the hole can be filled with wood putty.
If the stairs are open from the back, the squeak should be silenced from behind. The risers will either be butted or notched into each other. If the joint is notched, drive small wood wedges between the riser and the tread and secure them in place with a small nail or brad. If the joints are butted together, reinforce the butt joint with 8d nails driven through the bottom of the riser into the back edge of the tread.
Lastly, triangular wood blocks can be fastened to the riser and the tread above it with high-quality wood glue and secured with nails while bonding. This helps to increase the surface area of the tread load and eliminate future squeaks.
8d nails are two and one-half inches long and can be purchased at your local hardware store or home center along with high-quality wood glue.
Remember, always work safely.