An average family generates about 6 quarts of water a day. What doesn't go out the windows shows up in the attic and walls (often southside but thats another tale). If you have problems with water in a crawl space or basement - even more water in the attic. A whole house fan in the attic floor can contribute to the problem if the rest of the house is insulating but not the fan opening. Bathroom vents venting to the exterior? Is the house to tight? Does the laundry and bathroom room exhaust system really connected to the exterior vent. Is arrangement of vents in roof and soffits sufficient or do they just channel. Is moisture on rafters, etc found above bathroom areas (often the case). In addition to venting consider using a vapor barrier paint on the bathroom walls and ceilings. One possible serous source of moisture is your furnace (cracked heat exchanger)or improper flue system. Have it checked out even if you bought a new house. Good luck - no easy answer but you will end up with rotten sheathing and rafters if not brought under control.