Hi all, couple years ago I got a yellow line along a seam of drywall on the ceiling in the corner. here is a picture for illustration:
Picture of outside (so that its clear where vent holes are)
So 2 years ago after getting a stain (it was a line, so seems like a seam but I dont remember at this point). I opened it up, checked the roof above it for leaks (sprayed water on the roof, touched the wood from the inside, all was dry). I figured either water got blown in through the vent holes (since distance was under a foot) or something similar.
I patched it up and all was well for 2 years.
About a month ago, out of nowhere a different part of the roof got a stain, this was in accessible part of the attic and after going up there I found that there was a nickel sized damage to the paper backing of the drywall in that spot. I patched it up with some metallic tape (not sure if something like painter's tape would be better since its paper but I figured since we use metallic tape to keep water off surfaces it would be a good choice rather than something that breathes). Above the stained spot and all along the ceiling in both accessible and non accessible parts of the ceiling there is fiberglass insulation in sheets. When inspecting this spot I noticed that around the damaged paper backing there was a thin layer of moisture (both visible and wet to the touch), on top of it was a sheet of insulation, which was completely dry, so it was not a leak through the roof.
From what I've read and how I understand it, warm temperature inside the house contacted the cold air in the attic and formed condensation, which then stained the drywall. And contact was possible in that spot because of the damage to the paper backing. Inside humidity is around 60% and temperatures around 65 while outside is around 70% and air temperature is around 40 to 50. But we noticed that at night or mornings when outside temperature is low-ish the windows inside the house get all fogged up (like mirror in the bathroom after shower if you left the fan off).
Now a month later that patch panel from 2 years ago, it got water damage long the seam where I patched it. But not where previous stain was, but higher on the slope, where the top of the patch square is. Here is a picture with orange line indicating area of stain 2 years ago (approximate, it may have been a big higher, closer to center, otherwise I wouldnt cut a square that big), gray square showing the patch square and you can see the water damage along the top edge. The ceiling is sloped, so the stain is on the high side.
That part of the ceiling is not accessible. Whats the solution for this? How can I make sure condensation cant form on that side? Since as I put the piece of a drywall in I can only patch it from the inside of the house, not from the roof side, so that whole seam is 'damaged backing' because thats where the cut/seam is.
Would doing many layers of latex paint help? I dont think its a roof leak (since when I last opened the ceiling and checked everything I didnt find anything, and the stain is in a different spot, and just a month ago in accessible part of the ceiling I verified that it was not a leak but instead condensation on the back side). Id like to avoid opening it up again just to find nothing and patch it up again.
What should/can I do here?