Thanks to all for comments and suggestions. The house was built in 1969. It's a tri-level so there are two attics. The attic over the one story wing is no problem. The attic over the two story wing has the moisture problem. There is a basement under the one story. The first floor of the two story wing is garden level half in the ground. Heat is hot water baseboard. Humidity in the house runs about 40%. Shingles are composition fiberglass. When I bought the house in 1992 the roof had leaks where the fireplace chimney passed through the eave of the second story and the south slope over the single story was deteriorated from heat damage indicating a need for ventilation. I also installed a whole house attic fan in the second story ceiling ( I seal it in winter) which called for more attic vents. I didn/t notice any moisture problem before I reroofed and added ridge vents, but that doesn't mean that it didn't exist. It only occurs on the north slope in winter. The roof has very little slope and the eaves are 3' wide. That makes it hard to do much in the attic as it's only about 4' high center. It's a hip roof sloping down all sides, about 800sq ft. I noticed the moisture when I was running TV cable last winter. Sheathing and roof trusses were damp and showed mildew. Insullation is 4" of loose type which didn't appear damp.