I am building a new stairs to an outside deck. My question is about the stringers on the outside of the stairs. Is there an advantage or reason to cut out the notches in the stringers vs. leaving the boards uncut and just attaching a support that the stairs can be attached to? I realize that any stringers in the middle of the stairs must be cut, but leaving the outside stringers intact would seem to me to be a option that increases the strength of the stringers. Is the reason for cutting the stringers based on structural considerations or is it just for desired looks?
It’s basically a design choice, although leaving the stringers intact will definitely make the stairs stronger (as long as your treads are attached properly). Installing blocking with glue and screws to the stringers under the treads on either side is one option, but you can also eliminate the blocking by using a router or dado blade to inset the sides of each tread into the stringer and attach with glue and screws.
A quick and dirty option is to purchase precut PT stringers and adjust them to fit your deck height. If you’re cutting your own center stringer, be sure to treat the exposed untreated wood with a preservative. Depending on your stair design, 2×10 or 2×12 stringers have plenty of strength either way you decide to go.
Good luck, and I hope you make a ‘step’ in the right direction!