THIS IS IMPORTANT!!!

I got this product at home depot - installed above joists, with ply decking
immediately above, then glued-down membrane roof.

I didn't even think about interior/exterior.

Then, after roof was done, it rained. The beadboard scraps and cutoffs that
were left out delaminated, warped, buckled. So far no sign of trouble with
the installed pieces, but ...

exterior grade?

BB