Most SIPS panels have integrated joists at 24" o.c. So why would it be different than a traditional diaphragm design, yes I know the short side is not getting attachment. Also you can count on the "ceiling" diaphragm with the OSB on the bottom.
John Stensgaard, PE
------------------------------
John Stensgaard P.E., M.ASCE
PRESIDENT
S2E Consulting Engineers
Thornton CO
------------------------------