I am extending the width of my stairs, and need to remove the existing sub treads and risers. They appear to be glued (construction adhesive I'm guessing because it is brown) and nailed. Is this going to destroy the stair stringer when I remove them?
In case it is helpful, the reason why I am removing them is that I want to install new, wider subtreads and risers so that the wood flooring that is attached to them has a continuous surface. The new wider subtreads and risers would be attached to two new trus joist stringers that will be installed where the previous pony/cheek wall was (where you see the exposed 2x4s in the images below).
An alternative would be to just add new subtreads/risers for the additional width of the stairs, and make sure that they are level. But I think that is risky because there would be effectively 2 separate surfaces/platforms that the finished treads and risers would be attached to, which could lead to problems in terms of wood movement, etc. I'm trying to decide which is the less risky path.
Images
This one shows the best example of the effect I was trying to explain. I do not have a shot that shows how the handrail goes past the ceiling, but with a little imagination you could picture what the rail would have to do if the stairs were much wider at the bottom.
Best Answer
I think the least invasive way to handle this is to add two more stingers, one right against the existing stairs(essentially just a nailer) and one out at the ultimate width of the new treads. This way you don't have to remove the old sub-treads/risers or change the height of your treads, which would cause you grief when you get to the top of your staircase. Once you've got your new stringers in just apply sub-treads and riser to match the existing construction and you're good to go. The bigger problem is that no matter how you construct it, the landing or the the lower staircase will have to be modified to make the intersection work properly.
This illustration shows how the problem could be fixed by lengthening the landing and pushing the lower stairs out (assuming you can do this). You could accomplish the same effect by pushing the landing to the right but it looks like your landing is captured on that side in the pictures. Although this fixes the stairs the railing system will still have an unusual transition but it's not too bad depending on how far you need to extend your treads.