Is it a bad idea to install an impermeable moisture barrier over OSB flooring? In my 10x20 shed/office the OSB continues to off-gas after 5 months. It smells as bad as the day it was installed. I've read it can take up to 2 years to off-gas enough to not be smelly. Now I can eliminate this odor by putting down 4 mil plastic. But I have heard moisture will condense on the underside of the plastic, causing the OSB to mold. It is very moist here. Humidity averages 85 - 90%. Flooring Layers: A) the building is lifted 18" off the soil by concrete pillars. B) 2x6 joists nailed to 6x8 (treated/outdoor). C) 3/4" plywood (treated/outdoor). D) 3/8" cement board. E) 1/2" OSB.