A. Yes, there are a couple of things you can do. If there is a wide enough gap between the stairs and the wall, you can slide a long 1” x 12” into the gap. This would run the full length of the stair run and becomes a baseboard. This is frequently done after the stairs are framed and the wall board has been installed. It doesn’t have to be tight on the stair treads and risers if carpet is to be installed on the stairway. Similarly, hardwood treads and risers would be cut to fit snuggly against the trim board.

If there isn’t enough room to insert a trim board like this, or if one already exists, you could install a base-shoe on the treads. That is a piece of trim that looks a bit like a quarter-round, but is ½” x ¾”. The longer dimension is run up the wall and the narrower on the floor (or tread). If the treads have a rounded nose, you would stop each piece of base-shoe where the nose begins to curve. Cut the end with the same curve that the shoe has along its length, or ease it off with a sanding block.

If there is a gap where the risers meet the wall, it would look better to use a small cove mold there. You could run it up the end of the riser and then along the face under the nose.

If none of this sounds like the right solution for your stairway, it is possible to scribe a trim board to the stairs, but this is very time consuming and requires a lot of careful craftsmanship. You would lay the 1” x 12” against the wall on top of the stairs, and use a combination of levels, squares, and straight-edges to transfer the actual stair heights and depths to the board. Then you use a jig-saw, and possibly some clamps and straight-edges for guides, to cut away the waste. It is virtually impossible to do this perfectly, but you can get close enough to finish up with some caulk and a good paint job.