The sheathing on the inside of my roof  is soaking wet. I live in RI and have just put a new roof on my house (1 floor ranch). I have small soffit vents and a ridge vent (the brillo pad type). I also have gable vents.  In December, there was snow on my roof and it was raining. The sheathing was soaked!! I figured there was a cold surface (the roof with snow) and warm humid air (from the storm) blowing all around. Condensation..   How much soffit ventilation do I need?

I covered the gable vents to allow the soffit vents to do their thing. I also installed cellulose insulation above the R-19 fiberglass that was existing.