Stringer Hanger Board on 2x8 Joists???
I'd like you to imagine yourself jumping up and down, heavily, on that top step. Do you see how that plywood might tend to fold back under at the lower portion? And at the same time, begin to pull apart up by the floor level?
I think you could curtail this action by screwing and gluing in some 45° (or actually the angle of the stairs, not really 45) blocks of 2 x material right where the stringers are.
Wouldn't hurt to square off the upper back corners of those 45's and install a 2 x 4 ledger across the stair opening, snug up against those angle blocks so they can't shift rearward. Kind of like the 2 x that is affixed to the floor to keep the bottom of the stairs from sliding forward, the thrust plate. (Left drawing)
Of course, if you are able to actually extend the rear portions of those blocks up into the joist cavity, you could nail them to the sides of the joists..... but they would have be solid enough to brace the top ends of the stringers solidly from behind the plywood... and your joist layout may not be suitable for that. (Right drawing)
The whole idea of what I'm suggesting is to keep that plywood straight, flat and solid.
"True eloquence consists in saying all that is necessary, and only that which is."
François Duc de La Rochefoucauld
Last edited by Willie T; 02-28-2009 at 09:27 PM.