Wet cathedral ceiling

[jgold]

We just purchased a cabin here in Maine that we closed up last winter - drained the pipes, turned off the heat and electricity, etc. The cabin has a cathedral ceiling.

While checking on it last week (March), we noticed there were several areas on the ceiling that were very wet and had mildew on them -- obviously they'd been wet for a while.

The cabin was reroofed a couple of years ago and the roof looks OK. There were no ice dams, and in fact the side that was the dampest had almost no snow on it at all. There is, however, no ventilation in the roof -- no soffit or ridge vents that should be there.

I'm guessing that the moisture may not be a leak, but maybe condensation? My question is, since no one was living in the cabin and the water was turned off, would there be enough moisture to condense?

Or maybe I'm wrong on my theory and there is a leak. Any suggestions?

Thanks,

John

[trader4]

I'd get the venting put in, though that may be problematic too. Depends on how thick the insulation is that they put in and if they used plastic baffles. Since they didn't vent it correctly, who knows what they did there. Best case might be they were cheap and didn't put a lot of insulation in, leaving some space for air to pass thru.

Then, I'd keep an eye on it before repainting. After a few rain storms, in the spring, you should know the answer.

[m Ransley]

As George said it may be something other than a leak, get a Moisture Meter and get up there and test interior wallboard after a rain, maybe a simple fan high up left on over winter would fix it if no leak is found. Now it is possible drywall is wet so let it dry and test.

[George E. Cawthon]

By catherdral ceiling do you mean the ceiling is just the underside of the roof? if so how would you ventilate since there would be no open space between the ceiling and the roofing?

You moisture problem may be nothing more than a lack of ventilation in the cabin. Warm air in the lower part (assuming you have windows or the sun can hit the walls) rises to the ceiling which is cold with snow on the roof and the warm air cools and the moisture condense on the ceiling. A closed cabin can exhibit all sorts of problems that would not occur in a lived in building.

[trader4]

"By catherdral ceiling do you mean the ceiling is just the underside of the roof? if so how would you ventilate since there would be no open space between the ceiling and the roofing? "

If built correctly, there should be open space. At the top of the

2X8's you have the roof sheathing, at the bottom you have sheetrock. On the underside of the sheathing, plastic baffles should have been stapled forming a channel about an 1 1/2 thick running from top to bottom between the 2X8's. Then insulation is applied, barrier side down and stapled to the 2X8's, followed by sheetrock. A ridge vent goes in the peak, soffit vents at the bottom.

"You moisture problem may be nothing more than a lack of ventilation in the cabin. Warm air in the lower part (assuming you have windows or the sun can hit the walls) rises to the ceiling which is cold with snow on the roof and the warm air cools and the moisture condense on the ceiling. A closed cabin can exhibit all sorts of problems that would not occur in a lived in building. "

If a cathedral ceiling is not vented, you will have moisture problems. The most typical place for them to show is around openings for recessed lights.

[Philip Lewis]

This might go against your definition of "built correctly" but there are some cathedral ceilings which are built where you see the decking (which is usually some "nicer" wood) of the roof. Sucks for insulation mind you. (you can only insulate tween the roof decking and shingles) My friend has a "great hall" built like this. I think this is what George might be picturing. I believe the OP mentioned drywall, so unless the ceiling beams are exposed, and the drywall is directly attached to the sheathing between them, there is likely a gap like you describe. (perhaps not insulated/vented though)

I plan on opening up my attic space ceiling, so I want to understand your reasoning. From roof towards the inside: sheathing, 1.5" air gap made by vapor barrier, insulation, insulation's vapor barrier, and sheetrock?

I'm a little confused about the double vapor barrier. I thought the VB went on the "hot side". In this case it seems like you are considering both to be the hot side. ;) Perhaps the plastic sheet isn't meant as a VB, but rather just a vent channel?

My plan was going to be sheathing, preformed "C" vents, then spray foam, then sheetrock. The "c" vents would meet at the peak where I would pump the heated air to a location where it helps me most. (heat exchanger if interior calling for heat, outside at other times). The spray foam is a VB of it's own... so perhaps i could use the sheeting as you suggest to be a less expensive alternative to the preformed "C" vents.

I've also considered a "hot" roof (insulation all the way to the sheathing), but havn't been able to find enough info on it to determine appropriateness for my climate (Pittsburgh PA, USA).

[trader4]

"This might go against your definition of "built correctly" but there are some cathedral ceilings which are built where you see the decking (which is usually some "nicer" wood) of the roof. Sucks for insulation mind you. (you can only insulate tween the roof decking and shingles) My friend has a "great hall" built like this. I think this is what George might be picturing. I believe the OP mentioned drywall, so unless the ceiling beams are exposed, and the drywall is directly attached to the sheathing between them, there is likely a gap like you describe. (perhaps not insulated/vented though) "

Yes, you could have exposed rafters, but like you said, I think the OP has a finished sheetrock ceiling, which is the most common. There may not be an air gap channel though. With vent baffles there will be, but without, if you put too much insulation in, ie fill it all up anywhere, then the air is blocked.

I plan on opening up my attic space ceiling, so I want to understand your reasoning. From roof towards the inside: sheathing, 1.5" air gap made by vapor barrier, insulation, insulation's

vapor barrier, and sheetrock?

"I'm a little confused about the double vapor barrier. I thought the VB went on the "hot side". In this case it seems like you are considering both to be the hot side. ;) Perhaps the plastic sheet isn't meant as a VB, but rather just a vent channel? "

Exactly, they are vent baffles/channels, etc. Basicly a plastic chute, designed to keep an open channel for air to flow, not to insulate or be a vapor barrier. Available at home centers, building supply, etc. They should also be used in conventional attics for the couple of feet at the lower end of the rafters. There they keep that area open and free of insulation. Without them, what typically happens is the monkeys installing attic insulation push it all the way into the end, blocking the soffit vents. Had that exact problem in my house.

"My plan was going to be sheathing, preformed "C" vents, then spray foam, then sheetrock. The "c" vents would meet at the peak where I would pump the heated air to a location where it helps me most. (heat exchanger if interior calling for heat, outside at other times). The spray foam is a VB of it's own... so perhaps i could use the sheeting as you suggest to be a less expensive alternative to the preformed "C" vents. "

I don't know if you'd get enough benefit from this to make it worthwhile. In the coldest weather, the air would probably be colder than the inside air. It might be of some value on moderately cool days, but then you have the issue of controlling it, ie opening it/closing it depending on whether the air coming out is going to help or make it worse. If it's not automatic, then what? Likely you will lose more heat by leaving it set wrong, etc.

I've also considered a "hot" roof (insulation all the way to the sheathing), but havn't been able to find enough info on it to determine appropriateness for my climate (Pittsburgh PA, USA).

[George E. Cawthon]

There are different designs. One is with the beams at the bottom, some type of board (that composes the ceiling), a solid insulation layer (foam), wood sheathing, roofing.

A no insulation structure is no uncommon for cabins. And of course the type you stated, although 2x8 are a bit skimpy for insulation purposes.