l720 for granite

Is l720 for granite required because of weight only or is granite somehow more fragile? Was wondering if 2x2, s had same deflection requirement as 12x12,s?

Because they're fragile,
Same l/720 but with 2" you can get away with alot more.

I wondered if that was the case. I'm using 12x12x3/8 granite on a alcove tub platform top, front and about 3' high above the deck on walls. I went overkill on the tub framing, no-way it'll move. I would like to use same type granite 2x2s on the floor but it's not L720. FLOOR JOISTS are 9 1/2" I-joists on 12" centers spanning 15 1/2' topped with 3/4 osb. I shortened the span to about 14' with another perpendicular I-joist as a soffitt header above a bar in the basement but it's not truly load bearing in it's current state. I will probably beef up the webs on the joists and the header with osb and hope for the best. Would a sanded epoxy grout help if it were to deflect a little? THANKS P. S THE FLOOR TILE AREA IS 6 1/2' X (7 1/2')= (RUNNING WITH JOISTS)

You used OSB!

I know it's not as good as ext. Plywood but it was already in and from what I understand O. K to use under cbu. Tearing it out ain't gonna fly, ring shanked and glued to the joists. I could top it with 3/8 plywood and then cbu if need be if it would help L720. This whole build has been a P. I. T.a.

The 3/8 ply will help the deflection of the subflooring between joists but it wont solve the major issue of the unsupported joist span, nor will cbu which isnt structural at all. Can you sister new joists to the existing ones?

No, I can't get them in the basement. That's why I have to reinforce or you might say laminate osb in the web of the joists. Flitch plates you could call them. I wonder how much deflection I could get away with the 2x2 granite? I know its a loaded question! Anyone?