I'm rebuilding our staircase from the basement to the first level. The old treads and risers are out. The existing stringers are 2x 12's that were routed out and will be reused. I have access to underneath the staircase. My question is about the riser. Does the riser need to be drilled/nailed to the back of tread? Or can the riser rest on the tread below it and be drilled/nailed from below? I looked high and low for any reason or logic for or against putting the riser in between the treads.