Foam Board Insulation Moisture Problems
During the cold weather, warm inside air containing water vapor can get past the wall finish and insulation and condense inside the colder wall cavity. In climates that are hot-humid the same thing can happen, just in the opposite direction, humid outdoor air in the summer can condense inside cool/air conditioned wall cavities. If this will happen, root and moisture are very likely to occur. Because of this, building codes often require installing a vapor diffusion retarder on the warmest side of the wall cavity just to be on the safe side.
The foam board insulation is usually placed between the exterior finish and the studs of the outside walls. Preventing air infiltration is a must when dealing with foam board insulation, and that’s why you should place your rigid insulation boards tightly together and seal the seams with tape or caulk. Be aware though that this practice can worry some builders in cold climates since the foam board could act as a second vapor diffusion retarder. Although studies have shown that the condensation phenomenon rarely occurs in these areas unless something else is seriously wrong with the wall assembly.
