I built a new personal home in '07/08, finished March '08. It's a ranch style house with a garage that is perpendicular to the main house. The ridge of the main house runs North to South, with the garage roof running East to West. Over the garage is a bonus room. The main house has a 10/12 pitch, with the garage portion having a 12/12 pitch. GAP Cobra ridge vent is installed on both the main house roof and the garage roof. There is a sole 18" gable vent installed on the main house at the opposite end from the garage. That's my fault, as I told them to put it there not knowing it could cause problems with the ridge venting. The soffit is the perforated vinyl type, so it's vented as well. The roofs are also open to one another in the attic. Only slightly due to the bonus room, but open still.
Last week we got an accumulation of snow, a rarity around these parts, coupled with some very strong winds and a rapid rise in temperature after sunrise. Around noon that day, I noticed water dripping from one of the HVAC vents in the ceiling of the bonus room. By this time the snow was gone from the roof except for in the valleys. The drywall around the vent was damp and slightly stained. I got into the attic and found tiny water droplets on top of the insulation, directly underneath the ridge vent and for the entire span of the ridge vent. This was just on the garage portion. There wasn't a drop of water anywhere in the attic of the main house. Nor was there any water anywhere on the rafters or decking of the garage attic. So, I can only assume that snow blew through the ridge vent and into the attic, melted, and made its way through the HVAC vent cutout in the ceiling. There wasn't much water that got through, as the spot on the floor wasn't any larger than a half dollar and the bowl I placed under the drip didn't collect more than 1/4 cup at most. I didn't actually see snow in the attic, but the roof has never leaked before not even in other very strong wind/rain storms. This is the 2nd time it's been snowed on, but there weren't any strong winds associated with the 1st time.
Now having said all that, how do I best remedy this problem? Again we don't get much snow, maybe once or twice a year if that, but still I don't want mold nor do I want to repaint the ceiling every time it does happen. Will sealing off the gable vent fix it? On a 12/12 roof, it's hard to imagine how removing the ridge vent would be necessary, but I will if I have too. And it didn’t get through on roof where the gable vent is, so I'm not sure if that will take care of it or not. Thanks for your input.