Make sure the supply and return ceiling boxes are sealed between the boxes and the sheetrock as well as any other penetrations between the attic and house i.e. plumbing electrical etc. Condensation/ice will form on the coldest surfaces first. If it's cold enough you may be fighting thermal bridging not just air leaks.
Get a couple of ruuvitag:s. They monitor+record temperature, humidity and pressure. You can download history (10 days) off them. Put one on the outside (roof, covered from sun & rain) and one at the attic. Compare the readings. If you see humidity spikes, try to see what's causing them. But generally I think you're overreacting, there is no way in hell you're getting rid of the frost on the nails, that's just physics. The outside becomes colder much faster than your attic -> iron nail is cold bridge and will always condense moisture no matter how well you insulate
Make sure the supply and return ceiling boxes are sealed between the boxes and the sheetrock as well as any other penetrations between the attic and house i.e. plumbing electrical etc. Condensation/ice will form on the coldest surfaces first. If it's cold enough you may be fighting thermal bridging not just air leaks.
Get a couple of ruuvitag:s. They monitor+record temperature, humidity and pressure. You can download history (10 days) off them. Put one on the outside (roof, covered from sun & rain) and one at the attic. Compare the readings. If you see humidity spikes, try to see what's causing them.
But generally I think you're overreacting, there is no way in hell you're getting rid of the frost on the nails, that's just physics. The outside becomes colder much faster than your attic -> iron nail is cold bridge and will always condense moisture no matter how well you insulate
Spray foam between all the rafters/trusses
It is highly likely that your Supply Plenum is leaking warm air into Attic space.