Details: Original house built in 1930 and located in Cleveland, Ohio. Attic/roof structure has no soffits. Only ventilation is a 1' x 1' hole/vent cut out on east and west side of roof, about 1/3 of the way down from the top. New addition to house with attic built 2 years ago and has "soffits"/ridgeline structure.

Problem: Moisture is collecting in the attic causing mold and buckling floor-boards.

Question: Should I seal off the entire attic and make it a "non-vented" space? If so what type of insulation is best? If I should keep it vented, how do I keep moisture from collecting?