Bubbling drywall seams beneath foam cathedral ceiling
I see some bubbling along two seams in my cathedral ceiling drywall and would like to determine the likely culprit. The ceiling showed no indications of issues for more than one year.
The drywall isn’t sealed perfectly, this is my best guess. Yes, I have a few can lights and an exposed ridge beam that could be better sealed. Or maybe it’s the roof, finding it’s way through.
The ceiling is unvented, witch 6″ of cut-n-cobble rigid foam, followed by 3 to 4 inches of closed-cell spray foam.
This problem is recent, and follows many days of ice on my 12/2 roof. Any thoughts would be appreciated.
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Might be ice dams. I had similar issues last week with my addition with a low slope roof that was built poorly by the previous homeowner. Currently in the process of tearing into it to see what is causing it. I have heard that with low sloped roofs you should install more ice/water shield than on a normal pitch roof.
I doubt if the problem has anything to do with the drywall taping job. It sounds like moisture to me. The only way to figure out what is going on is to open up part of the ceiling.
Your insulation method is unusual, and doesn't follow any of the methods recommended here on GBA. The cut-and-cobble method is associated with failures when used on an unvented roof assembly, for one thing. Your mention of "a few can lights and an exposed ridge beam that could be better sealed" is not encouraging.
An insulated ceiling assembly should never include can lights.
I'm just guessing, but it's entirely possible that warm, humid interior air is entering your ceiling assembly through the can lights, and it traveling along gaps associated with your cut-and-cobble job. Moisture in the air is probably turning into water or ice when the moisture encounters cold sheathing, and the water is tricking down through cracks until it encounters the drywall.
But that's a guess. The larger the area of your roof assembly you can open up, the more likely you'll understand the mechanism.
Warm humid air from the interior and the cracks and gaps that I have not been diligent enough in sealing, was my primary concern.
However I believe the only cold surface would be due to bridging into the rafters and ridge beam; I covered that cobble job with 3 to 4 inches of cc spray foam.
Would it be possible that warm air is entering through cracks between the ridge beam and drywall, condensing on the rafters and beam that are not buried in foam?
Q. "Would it be possible that warm air is entering through cracks between the ridge beam and drywall, condensing on the rafters and beam that are not buried in foam?"
A. It's certainly possible.
I asked a dumb question. Thank you for making that clear.