It's an old house and a couple of the stair risers have gotten pushed in at the bottom where the step and the riser meet resulting in a gap of up to nearly 1" in places. There's no access to the stairs from underneath.
I'm considering two options:
1. attach a replacement riser over the old ones since there's a pretty decent amount of overhang on the steps.
2. embed a screw partway and try to pull out the riser so it meets the step. I don't think this will work, since there are visible nails that have been pulled out along the sides. Also even if I can pull the riser back in place, I don't know how I'd keep it there.
Since I have two steps with the same problem, I'm guessing this can't be all that unusual a problem. Is there is standard way of making this repair?
I'm going to leave it to the professionals here for the repair suggestions. But it sounds like your treads and risers are mortised into the stringers and the stringers are spreading apart a little thus allowing the risers to slip back in the opening. Of course they have had a little help slipping.
It sounds like the wedges in back of the risers fell out . Older staircases had them under the treads and behind the risers. They were glued in place and 3 penny finish nail driven through the wedge into the stringer. Over time the glue dried out and the constant vibration loosens the nail.
Repair method requires opening the area under the staircase and replacing the wedges.
What do you mean, there's no access under the stairs?
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
B. Franklin 1759