Recently I spent some time in a very wet attic space of a new home. The problem was a lack of adequate venting. Older homes tended to be able to get away with less venting because of the type of construction as there were a lot of drafts throughout the home, newer homes not so much. What happens is the warm moist air inside the home rises up through the ceiling. When this air makes contact with the cold attic space in the winter it turns to frost and creates dampness in the ceilings or even ice damming on the roof.  In summer lack of venting makes for a hot attic space that can make the home unbearably warm and even ruin your shingles.