Stair Treads

[mwj]

I have a 42" wide staircase in my entry way. The stair contractor has one 2x12" stringer on each side with 5/8" OSB for the stair treads which will get 3/4" engineered oak treads glued and nailed on top of the OSB treads. There are 5/8" riser boards. Will the treads sag in the middle without a middle stringer?

 

[C.J.]

I don’t like that much. The 5/8” OSB by itself is worthless. 3/4” treads would be decent if you had a middle stringer. 3/4” + 5/8” = 1.375”, which itself would prolly span 42” adequately, but you don’t have 1.375”, you have two pieces that together add up to 1.375. It’s not the same thing. I guarantee you you’re gonna get a squiggles worth of adhesive and a few nails to hold the treads in place on the 5/8”. That’s not the same as if those 2 pieces of wood were fully glued together as one piece. I would want a middle stringer.