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barbaraizac 09-20-2009 12:16 PM

Condensation on cathedral ceiling
Last December I replaced the composition shingle roof on my entire house. The master bedroom & bath addition, built by the previous owners, had two layers of comp shingles that had to be removed. The master bedroom has a cathedral ceiling and the drywall is attached directly to the rafters, which I'm guessing are 2x6. I am assuming that there is some type of insulation between the two, but I have not yet drilled into the ceiling to make sure.

I live in Southern California and we have had a really hot summer. About three months ago, I noticed that the ceiling was wet about two feet above the skylight (installed in 1991). I immediately called out the roofer to check the flashing. It checked out okay and he told me that I must have a leaking pipe in the ceiling. Then I called out a plumber, and he confirmed that there are no pipes in the ceiling. The wet spot, which I believe to be condensation, is evenly dispersed over a 2x2' section. It appears overnight and then disappears during the day. I got the roofer to come out again two days ago and he installed an O'Haven roofing vent right over the trouble spot. It has failed to correct the problem. I went up on the roof with him when he installed it, and to my horror, I found that the entire section of roofing over the cathedral ceiling was damp. The rest of my roof (with a crawlspace below) was dry. When he pulled up the shingles to install the vent, the paper (felt) was dry.

My question is this: Why did this problem occur following the installation of the new roof? Is it possible that because there were two layers of shingles there before that they kept the heat down and prevented the condensation problem? If not, is it possible that there was some kind of insulation between the old roof and sheathing before that isn't there now?

Please help. I lost my husband to cancer recently and I am lost as far as what to do. I know I need to improve the ventilation, but no one I've talked to can agree on how to do that. I spoke with a contractor who lives down the street, and he told me that I need to remove my roof and put down rigid insulation. Another friend, who works as a handyman, told me I should have solid foam insulation blown into the rafter space (assuming there is no insulation there now). Yet another told me to get a ridge vent. Aaaaaargh! I'm so confused!

mics_54 09-20-2009 12:59 PM

Sorry for your loss and your difficulties.

You apparently have inaddiquate insulation and ventilation in the small space in the roof above your cathedral ceiling. As you probably know warm moist air can condensate upon relatively cooler surfaces under certain conditions. It's not easily predicted if you have sufficient space with a 2x6 rafter to get addiquate insulation to eliminate the dew point circumstances that create the condensate. Unfortunately there are no "cheap" fixes although some may be less costly than others.

Did you change the color of the roof when you had it re-shingled? Making the roof darker would probably cause the space to become warmer. This could have created the circumstances where the dew point was reached where it had not previously.

Unfortunately adding a little ventilation may actually make the problem worse in that it would keep the area supplied with more moisture layden air.

stuart45 09-20-2009 06:39 PM

When the air in the roof space is really hot in the day it will hold a lot of moisture. This will often come from the moisture produced in the house from every day living such as cooking, drying clothes or breathing. At night the roof will loose heat by radiation, especially to your clear blue Californian sky. As the temperature drops condensation is likely to happen in the space. Ventilation will help prevent this as long as the moisture content is lower in the outside air. In the UK condensation in the roof spaces has become a much bigger problem since people started using insulation between the joists in the 60's.

barbaraizac 09-20-2009 07:24 PM

condensation problem on cathedral ceiling
The color of the new shingles are the same color as the old ones. The only thing that has changed is that there is now one layer of roofing instead of two. My biggest struggle is that no one can agree on what to do.

I have a building contractor coming over tomorrow evening who was a good friend of my late husband. I really need to understand the structure of the roof better, and he will help me do that.

mics_54 09-20-2009 09:51 PM

I suppose its "possible" that two layers of shingles kept the roof/rafter space temperatures from reaching a dew point that one layer doesn't. It doesn't seem likely though. It sounds fishy that it wasn't wet before a new roofing job and now it is.
I'm sure your contractor friend can figure it out.

Interesting that the wet rafter space is directly above the skylight. That space probably doesnt have any air flow from the eaves to the ridge because the skylight blocks the space off.

You probably have a vapor barrier benieth the sheetrock on the ceiling. You contractor can check for one at openings like light fixtures (maybe) or in the attic access area.

It's a mystery.

stuart45 09-21-2009 06:01 AM

Vapour checks often get damaged when things like skylights are installed. I would be surprised if changing the roof covering had caused a condensation problem.

barbaraizac 09-21-2009 06:06 AM

Condensation Problem
The skylight went in in 1991 and has never caused even the slightest condensation problem in all that time.

mics_54 09-21-2009 09:02 AM


The skylight went in in 1991 and has never caused even the slightest condensation problem in all that time.
that you know of. The skylight is penetrating the cant penetrate the roof without blocking off airflow from the eave to the ridge.

Not saying its causing condensation...but im not saying it isnt either. But if it'd likely not know unless it was bad.

stuart45 09-21-2009 09:21 AM

Is it possible that you have had an exeptionally hot humid summer, with colder nighttime temperatures which could have altered the balance and caused the condensation. For one layer of shingles to make the difference, the surface temperatures of the roof elements must have been very close to the dew points in the original roof.

mics_54 09-21-2009 09:45 AM

....not to mention that a little condensation on sheetrock wouldnt be noticed...repeated condensation eventually saturates the sheetrock. Heat transfer characteristics of saturated drywall are different than dry sheetrock. The moisture causes it to transfer heat more readily and make the problem even worse. Insulation is probably also getting damp making it less effective. Over time the problem becomes noticable from a distance....mold begins to appear...paint begins to smell.

barbaraizac 09-21-2009 10:24 AM

The humidity is high here. I live less than a mile from the beach.

So do you think that rigid insulation would help? I know I need to take care of the problem before I get mold, wood rot, termites, etc.

Meanwhile I'm pretty sure that the swine flu has me in its grips. Feels like I've been run over by a bus. Aaaaaargh!

mics_54 09-21-2009 01:34 PM

ridgid or sprayed foam would give you the greatest R value per inch. (around R7/in) All the issues have to be addressed/checked. Insulation, vapor inflitration, ventilation. Let us know what your contractor says!

barbaraizac 09-21-2009 04:43 PM

Am down with the flu. Sick as a dog (PIG?), so I called the contractor and told him we'll have to reschedule his inspection. Bad timing to get sick!

stuart45 09-21-2009 05:23 PM

Get well soon barbaraizac.
As mics 54 said there are a number of issues to be checked which can only be done on site. When surveyors check a property for condensation they take the R/H and temperatures of inside the roof space, inside the property and outside. They also use a surface thermometer to take the temperatures of the building elements involved. A number of these readings are taken during the day and night. This can pinpoint when and where condensation is taking place.

AaronB 09-21-2009 09:59 PM

Did the roofers replace any decking in the area above the skylight?

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