Finally, attics can get hot and uncomfortably damp in humid weather. Be sure to properly ventilate the attic. If the attic does not have a vapor barrier (which may not be a necessity in many cases), it should have one square foot of venting per 150 square feet of attic, according to MSU research. For areas with vapor barriers, one foot of venting per 300 square feet of attic is acceptable.

Humid weather can cause a variety of home problems and hazards, but they can all be prevented or remedied with some care and diligence.

Source: http://www.networx.com/article/how-humidity-can-damage-your-home