Staircase Reinforcement

March 3rd, 2025 - The stairs from first floor to second floor need to be repaired. The treads and risers creak, bow, and some are cracked. I began careful demolition last weekend, removing all the drywall from below the stairs. The plain 2x4s in the photo are not part of the stairs; the drywall was affixed to them. Initial plan is to remove the drywall framing, then add one or two stringers. A 2x12 stringer would be strong enough, and I think it is what building code requires, but it would be lower than the drywall ceiling I took out. A 2x10 might be the perfect fit, but after all the needed cuts, it might not be strong enough. Steel stringer? Build a rectangular brace (rough design pictured)? Use 2x12(s) anyway and replace basement stairs with slide or spiral staircase?

March 30th, 2025 -  Attach the red dot pieces to existing side stingers first, with just enough room to wedge the top piece, preassembled with all three green dot pieces, into place; thus pushing the tread up. Screw bottom green dot pieces into red dot pieces. Test fit before using screws, real fit with construction adhesive on very top, and top and bottom of red dot pieces.