Here are three simple steps (no pun intended) that can help you fix a loose or squeaky staircase:
1. The first order of business will be to walk up and down the steps to identify the loose treads. Once located, you can drive glue-coated wooden wedges into the tread seams where needed. You can also opt to fasten small wooden blocks along the front seams with glue and several screws.
The back edge of the tread may shift. If this happens the next task is to drill pilot holes and screw the tread down tightly to the riser.
2. You are now ready to cut and insert a new wedge. We suggest tapping the new wedge in tightly and using glue to bond it. If working under the stairs is difficult you can always drive wedges into seams from above. You can accomplish this task by using thin shingle scraps coated with glue ad trimming them flush with a handy utility knife.
3. The front edge of a tread can be nailed to a riser. Again, you will need to drill pilot holes and follow by driving in pairs of ringed-shank finishing nails preferably angled towards each other. Now finish off and sink them with a nail set-filing the holes with wood putty.
If you plan on carpeting your stairs later, go ahead and substitute long, thin flathead screws for stronger holding power.
There are a lot of intricate joints in the majority of stairs, and the general methods a person will take to make repairs are about as infinite as there are people on the planet.
If you feel you are in over your head you can always have an experienced carpenter sit in for the challenge. At the end of day the main goal is to have a staircase that is functional and safe to navigate.