barrel vault condensation problem

This house has three barrel vaults clad with copper, flat seam on top and standing seam on the sidewalls.

This is an old picture from when I cleaned the roof, I didn't have the camera with me yesterday. One of the barrel vaults has had intermittent leak problems. There is a weak detail where the valley meets the tile that the origional roofer has worked to repair and I did a repair on back when I cleaned the roof. But when the leak returned, we removed some wet sheetrock to try and find the leak and found the sidewall sheathing soaked. Since it was wet in spots that couldn't possibly come from the weak detail, I'm suspecting ventilation issues. There is no venting in the barrel vaulted area. The moisture on the sidewall was a light film of water instead of a concentrated drip like a roof leak. There was no vapor barrier/retarder between the sheetrock and framing.

I am thinking of recommending they remove the sheetrock (a pretty elaborate job on the barrel vault) and then trying to figure out where to incorporate some kind of venting into the copper roof and/or sidewalls. Then having a vapor barrier installed above the sheetrock. It's alot of work to have done just on a theory of invisible vapor.

Of the three barrel vaults, only one has ever caused a noticable problem. My theory as to why that is, is that it's the only one that gets the air from the great room area, which has arena-sized air vollume.

Any advice or criticism of my solution would be appreciated.

Jed, the problem is on the South side of the barrel vault that's behind the tree in the right of the picture. It's the lowest. But it's also the only one that opens to the great room, though, which has a huge vollume of air in it.

Gerry, there's roll insulation in the sidewall. I don't know what's in the cieling, but I'm sure they have some. There is no poly behind it. I was in the attic around the leaking vault and there was no way to see anything in the vault, but the rest of the attic was bone dry.

What kind of insulation in behind the sheetrock? Maybe someone never put poly on the vault before the drywallers came. Just a thought. With the film of water it does sound like a condensation problem. Is there any way of telling if the other 2 vaults have poly installed if you go up into the attic space and look?

Woody, Is the problem barrel vault higher than the rest?