I need advice solving a condensation problem on the inside of my garage wall.
The garage is bordered on two sides by heated living space and is insulated but not actively heated. It maintains a moderate temperature year round. The back wall has a direct southern exposure and its construction is 2X6 with fiberglass insulation and 6mil plastic vapor barrier on the inside.
The problem is that during sunny days in the late fall and especially early spring, condensation forms on the stud side of the vapor barrier on the back wall. This happens because cold overnight temps cool the garage down and then the sun heats the outside of the wall driving the warmer moist air inward. The moisture is enough to discolor the studs and insulation and I believe it will cause damage over time. I can not simply remove the vapor barrier inside because during the winter I will experience the opposite effect and rot the exterior.
The only possible solution I have found so far is to pull the plastic and fiberglass out and spray the inside of the exterior sheathing with at least one inch of expanding foam insulation, then replace the fiberglass and leave the plastic off. I read that this would both act as a vapor barrier and provide enough thermal isolation to prevent condensation. However, this info was from a foam manufacturer and could not be verified.
Any thoughts, advice or expertise would be greatly appreciated.
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