Why is There Frost on My Interior Walls and Ceilings?

 The typical answer I give my clients when they ask that question is your humidity inside the home is too high and you may have insulation deficiencies.
 During the winter months, especially here in the Chicago area, it is important to maintain your Indoor Relative Humidity between 30%-50%.Warm air moves from warm to cold during the winter months. If your humidity is elevated, let's say in the 60% to 80% range you may notice frost forming in attics or on interior walls and ceilings.
 Frost may form in your attic on the roof sheathing as a result of inadequate ventilation or inadequate insulation. Warm moist air will enter the attic through improperly sealed attic access doors,light fixture electrical boxes and any other unsealed openings into the attic. As the weather warms up, the sun warms the frosted areas which melts the frost and it begins to make its way back into the home through light fixtures and ventilation fan openings.
 When your exterior walls are improperly insulated, the moist air will find its way through your interior walls and find the cold spots and frost will form behind the drywall and even on the drywall inside the home.
 This then can become an indoor air quality issue as mold has a nice moist area to grow. Bottom line is maintain your Indoor Relative Humidity around 30%-50% and these problems should not occur.