We've had ongoing issues with humidity in our attic, and now I think I know why... Some background: We bought a traditional colonial, in southern New England, with an unfinished attic two years ago. The house is 23 years old, the roof is about 5. The fascia boards have full drip edge venting and a ridge vent runs the length of the house. No soffit vents. On top of the FG insulation in the attic floor, we blew in additional cellulose insulation. The installers did a mediocre job of installing the plastic chutes between the joists, and used smaller ones than I would have used. I had the gutters cleaned and gutter guards removed. The gutters were clean, no buildup. I thought the gutter guards might have been blocking some airflow to the drip edge vents. Over the course of the winter, I noticed some frost on exposed nails in the attic. There's also some light mold on an area of the inside part of the roof, which I thought was caused by a poorly sealed attic ladder. I also noticed drip lines in the cellulose. I thought it lined up with the exposed nails. I've also noticed a couple of places on the second floor (below the attic) where there's some light water staining on the celing. Not much, and most of it is by the ceiling/wall intersection. There's at least one area that's nowhere near the wall. However... This weekend we had heavy rain and wind. I went back up to the attic to check this morning and found that it's really humid. I also noticed more drip lines in the cellulose, and they align to the ceiling joists. Interestingly, they also align to the plywood underlayment joints. In the attached photo, you can see the drip lines in the cellulose. Most, perhaps all of the dripping is on the northeast side of the house, which doesn't get much sun. I assumed that this was a winter issue due to less heating of the northeast side versus the southwest. So here's my hypothesis: Windblown rain, usually from the north, gets in past the ridge vent and travels down the roofing joists. Some gets diverted at the plywood joints and travels horizontally. Some drips down as it travels, and some ends up at the bottom of the joist, staining the ceiling. So...it looks like I need to get someone to inspect, and probably replace, the ridge vent. And to improve the air flow, I probably need to clear out the insulation at the lower edge of the roof and install larger air chutes. Because of the standing cellulose, that's going to be a PITA. Does this make sense, or am I all wet?