A. Corresponding editor Paul Fisette replies: Your observation is correct: Climate has an impact on the specification of a weather barrier system. I would not recommend using a membrane like Grace's rubberized product over wall sheathing in a heating climate. It is impermeable, and it forms a powerful cold-side vapor barrier. If water or vapor leaks into a wall cavity that has a tight "rubberized" covering on the exterior cold surface and an impermeable vapor retarder installed on the warm interior surface of the wall, it will be trapped there.

But in your hot, humid climate, a low-perm membrane applied facing the warm exterior could work. It is important to build the wall so that it's able to dry toward the inside when conditions dictate -- in other words, don't apply a poly vapor barrier or vinyl wallpaper to the interior.

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