Water damage along drywall seam due to humidity, how to solve this problem?

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?

Thanks!

 

It sounds like you are missing a vapor barrier.
Cold air should not be allowed to contact the back of the sheetrock.
The back of the sheetrock will be very warm from the heat from inside the room.

You may need more insulation too.
You can't fix the problem from below the ceiling.

 

How do I fix it then? If I am going to open up the ceiling again, whats the proper fix? The insulation that is there takes up the entire space (probably 4 to 6 inches) and it does have a paper backing.

The vents to the outside are right there a few inches away, so Im not sure any amount of insulation would keep cold air from going in there, would have to close off the vents.

 

Those round vents are intake, didn't see you mention what you have for exhaust venting, ridge vent or gable vent, or other?
You are dealing with a typical attic venting problem that becomes more difficult with the limited space of a sloped ceiling. These intake holes can also be competing with other intake which we cannot see. An outside picture of the house might help.
A nearby big city would give us your climate zone.
60% RH on the inside is high. Air leaking into your walls can find its way through the top plate into the attic.

Bud

 

The climate zone is Southern California (LA). The venting is Dormer Vents at the peak of the attic. But that space between drywall and the roof is filled with fiberglass insulation so Im not sure how much airflow actually makes it through. The stain in the accessible part of the attic I mentioned (where the backing paper of the drywall was damaged) is right below those vents though, so definitely airflow there.

 

There is supposed to be a 1 or 2" space above that fiberglass insulation.

Except for current weather I doubt you have been dealing with light powdery snow, which can blow through gable vents. But rain can also in some conditions.

The reason I asked for pictures of the house is to identify any other low venting. When a house has soffit vents at different elevations the ones in the middle can end up with little air movement.

The missing patch of backing paper on the drywall simply means any moisture will soak through faster, but it isn't the source of your problem. Being LA even condensation is a low probability.

Why is your inside humidity so high? "Inside humidity is around 60% and temperatures around 65 while outside is around 70% and air temperature is around 40 to 50."

Use this dew point calculator to see what happens when inside air gets cooled.
Dew Point Calculator

Inside RH needs to be 35% or so. What are you doing to make it 60%?

Bud

 

Not doing anything, its been raining/wet for a week or so, everything has been locked up due to it being cold (days 55, nights 45) (no fresh air from outside) thats why humidity is so high inside. I have humidity meters in different rooms. Right now its around 55%. Thats pretty typical for around here, its rare that we get under 40% humidity outside, if we do its usually absolutely terrible for allergies and is due to an atmospheric event like Santa Anas.

Im surprised to hear that its should be 35%. All my meters give normal range as between 40% and 60%.