Attic Condensation

This very much sounds like a situation where the metal is transmitting cold to the roof deck and it's just enough to hit dewpoint, causing condensation in the attic. I do not run into this often but I have on occasion. Solutions include increasing ventilation in the attic (or making sure the current ventilation is working). You can test for airflow in the attic using a smoke pen or even a light piece of tissue paper held near the ridge. Reducing the moisture level in the home would also be helpful. And, of course, that bathroom vent needs to be vented outside. Now, sealing off the living space is also a very good idea but, if you have insulation down and no vapor barrier, it's hard to do that 100%. Sealing around your attic access would be good. Using an oil base moisture resistant paint on ceilings and walls would also be helpful. But, for now, I'd check the ventilation, vent the bathroom vent to the outside, and see if moisture levels inside the home can be dropped perhaps by a dehumidifier.

We had a metal roof installed this summer. At the first snow this winter, we noticed the plywood in the attic was wet. It seems to be condensation, since it was fairly uniformly wet over all areas of the plywood. Now mold is growing on the plywood already. The house is 960 square feet, so it is a small home. We run a wood stove for heat in the winter, along with a supporting heat pump. We have a drop down door/ladder to access the attic, with a small area floored for storage. We have blown insulation along the floor of the attic, along with rolled insulation on top of that. We have soffit vents that run along the edge of the bottom of the roof, and a ridge vent that runs along the top. We do have a bathroom fan that is vented directly into the attic (which we have now learned is a mistake). When the metal roof was installed, they removed the asphalt shingles, put down tar/felt paper and then the metal. The condensation only seems to appear when it snows, and there is snow sitting on top of the metal roof. We have researched possible causes and have found a lot of information online, making it difficult to discern what the cause actually is, and therefore how to begin to try to fix it. Our primary issue with much of the information about ventilation and sealing off the living space from the attic to prevent moisture from getting up there is that the condensation never occurred with the asphalt shingles. It only began with the addition of the metal roof. Our roofer said he had never seen anything like this and could not provide any information on what might be the cause or how to fix it. We have talked to some energy efficiency people who said we need to seal off the living space air tight from the attic to prevent the moist air from getting up there. But we live in a climate that is extremely humid, so the outside air coming in through the soffit is already moist. And the condensation only started with the installation of the metal roof. We have found lots of information online about causes and solutions, but feel like we're not sure what is the most likely issue and fix and could really use some help with finding the best course of action to take. We're not sure if the roofer did something incorrectly and just does not want to deal with it, or if it is a separate issue altogether. Any help you can provide would be most appreciated!