Air and vapour barriers
Interior sheathing as an air and vapour or vapor barrier
...and the ensuing damage that comes with it. In summer however, with the combination of hot, humid days and air-conditioned, dry interiors, the vapour drive reverses and can force moist air inwards through your insulation where it can condense on a cold and impermeable vapour barrier.
Ideally we'd have no vapour barrier ...