I'm gutting a terrible basement refinish attempt by a previous owner and trying to save any building materials I can reuse. One of those materials is polyisocyanurate insulation. There are about 30 4x8 sheets behind stud walls. I'm reading mixed info about using ISO below grade. The stuff is pretty impermeable so it seems to me like putting it against the exterior wall would make a cold-side moisture barrier. Does anyone know if ISO will cause problems below grade? It's DOW Super Tuff-R 1" R6.5. Thanks.