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Old 01-17-2007, 09:57 AM   #1
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Cathedral Ceiling Sweats


I have a cathedral ceiling that sweats in the winter. It has a 6/12 pitch, 2x12 rafters, and 16 inch centers. It started out with ridge vent, dura vent, and vented sulfate with R19 insulation. So I took the ridge vent off, plugged both ends of the dura vent, repeated that process again. Covered all inside of ceiling with bubble wrap, and then 3/4 tongue and groove oak. It now has three layers of plastic, one layer of bubble wrap, and a total of R41 insulation. It Still Sweats!!! I really need some suggestions on what to do next!
Thanks,
Dan H

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Old 01-17-2007, 10:45 AM   #2
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Cathedral Ceiling Sweats


Do you have a metal roof? If so I'm having the same problem!

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Old 01-17-2007, 04:53 PM   #3
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Do you have a metal roof? If so I'm having the same problem!
I do not have a metal roof, I have shingles.
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Old 01-18-2007, 12:25 AM   #4
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Cathedral Ceiling Sweats


Hello,

You sound like you have created a triple vapor barrier. This will trap moisture between the layers of plastic. You will need to get rid of two layers of plastic.
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Old 01-18-2007, 12:28 AM   #5
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Cathedral Ceiling Sweats


Hello,

Are the layers on top of one another or are they seperated? If they are 1 after the other then that shouldn't be a problem. If they are seperated with insulation inbetween thaen that is a problem.
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Old 01-18-2007, 02:28 PM   #6
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I'm making the assumption it is sweating inside the house and not above. Have you checked the humidity levels in the house and at the ceiling? Condensation happens when warm air (which holds more moisture) hits a colder surface or airmass, cools rapidly and releases the moisture. Typically most homes are pretty well closed off in the winter and the humidity levels tend to creep up (particularly if you burn anything for heat and if your vent fans in the bath are either inefficient, missing or not used). You may need to control the humidity.
The opposite can happen during the summer, particularly in attic spaces, which is why you want good airflow (we always recommend active vent fans in attics and crawlspaces hooked to a thermostat and a humidistat).
Also, with a vapor barrier, make sure you aren't trapping moisture or at some point you will be calling me or one of my associates.

Last edited by MoldBuster; 01-18-2007 at 02:30 PM.
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Old 01-18-2007, 04:57 PM   #7
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Cathedral Ceiling Sweats


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Hello,

Are the layers on top of one another or are they seperated? If they are 1 after the other then that shouldn't be a problem. If they are seperated with insulation inbetween thaen that is a problem.

As of right now they are seperated with insulation. Should I take all plastic down and the bubble wrap that covers the whole ceiling, or should I leave the bubble wrap for a heat barrior? Any suggestions would be appricated!
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Old 01-18-2007, 05:01 PM   #8
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If you have bubble wrap covering the entire ceiling where it is sweating on the inside then yeah...definitely take it down! You'll end up with growth if you trap that moisture. You can try putting in a fan on low to get some circulation (assuming it isn't a leak) which will help to keep things from condensing. I suspect humidity control will be your answer.
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Old 01-18-2007, 07:27 PM   #9
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Cathedral Ceiling Sweats


Can you describe your roof system in a little more detail? For instance:

From the outside in, I have: Asphalt shingles, roofing felt, 1/2" plywood sheathing, 2"x12" rafters with 6" of pink insulation between them (with an air space above the ins. and below the sheathing that is open to the outside at soffit and ridge), 6 mil. poly vapour barrier, drywall.

This would help a great deal, it worries me that you say you have three vb's with insulation between them.

Also where are you located, this has a great deal of bearing on moisture issues.
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Old 01-19-2007, 06:24 PM   #10
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Can you describe your roof system in a little more detail? For instance:

From the outside in, I have: Asphalt shingles, roofing felt, 1/2" plywood sheathing, 2"x12" rafters with 6" of pink insulation between them (with an air space above the ins. and below the sheathing that is open to the outside at soffit and ridge), 6 mil. poly vapour barrier, drywall.

This would help a great deal, it worries me that you say you have three vb's with insulation between them.

Also where are you located, this has a great deal of bearing on moisture issues.
From the outside in, I have: Asphalt shingles, roofing felt, 1/2" plywood sheathing, 2"x12" rafters with dura vent stapled to the underside of the plywood from top to bottom, it was vented from ridge vent to sulfate, now it is plugged on both ends. Under that is plastic from top to bottom, under that is R19 insulation top to bottom, followed by plastic again, then R19 again, then covered all inside of cathedral with plastic and bubblewrap. I then put up 3/4 inch tongue and groove oak to finish. I am located in Western Maryland.Temp today was 22 degrees with a lot of wind.
Thanks,
Dan
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Old 01-21-2007, 03:36 PM   #11
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Whoa! That sounds like a vapor trapping sandwich and may explain why you have condensation. You need to remove the plastic between the layers of insulation. With two layers of plastic, moisture can build up in the insulation layer in the middle and it becomes heavy and ineffective (cold). Typically, there should be one vapor barrier only...you have 4. Common practice when using batt insulation is to use faced bats on the bottom with the batt vapor barrier facing downwards and stapled to the joists and NO plastic vapor barrier. Then a second layer of UNFACED batt insulation. If you have installed plastic to the bottom side of the joists just under your T&G Oak, you should have used unfaced insulation (if you used faced insulation...you have 6 vapor barriers which HAS to be a record!) and it needs to fill the joist cavity all the way down to the top layer of the ceiling. Also, when you say you used plastic sheeting and "Bubble Wrap" between the bottom of the roof joists and your T&G Oak ...are you talking about a bubble radient barrier? Or are you talking bubble wrap as in wrapping something in it and shipping it? If you are talking radient barrier (proper radient barrier has two layers of bubble wrap sandwiching a layer of reflective foil in the middle, then it should have been the only vapor barrier installed and you should have tuck taped all the joints or the vapor barrier is ineffective. Using a second layer may trap moisture. If you are talking about pack it and ship it bubble wrap...

You also want to open up the attic ventilation again. If I understand you correctly...you installed vent chutes from the soffit vents all the way up to the top of the ridge vent? And then you installed plastic to the underside of the entire roof structure? This is incorrect. First off, there will be little to no airflow thru those spaces under the soffit vent chutes. Airflow thru a ridge vent system depends on a temperature differential and there won't be enough of one to set up much of an active airflow. Combine that with the plastic underneath and you may totally mold/rot your roof sheathing out. There should be one soffit chute installed at the soffit vent side and my strong opinion is that the plastic needs to go bye bye. The purpose of the soffit chute is to provide an airflow channel where the insulation meets the roofline to keep the insulation from plugging the ventilation. Assuming I understood what you did, your entire attic space has been closed off from ventilation. Also, I am thinking that plastic layer on top will trap moisture on the underside from temperature differences and it is going to drip down, land on the top insulation, drip down to the plastic layer and sit there getting stagnent and trying to find someplace to go. It will also run down the plastic and then down inside your walls if the roof pitch is high enough. This is a guaranteed recipe for mold and rot. You need to provide for airflow exchange thru your attic space. I spend a lot of time adding MORE airflow when we remediate moldy attics and end up opening soffit vents all the time that are plugged with blown in or had no soffit vent chutes installed (or they used those #$%#'ing cardboard chutes that rot and/or collapse). I usually recommend my clients add MORE airflow thru active vent fans (with a thermostat and a humidistat). If you want to put up a radient barrier in the attic to the underside of the roof joists, it is not a bad idea but the radient barrier needs to be the PERFORATED foil type (this is what I used in my home). At this point, I'd strongly recommend you hire a highly experienced home inspector to come out and consult with you. I am fairly certain they will tell you the same things I did. I'd also recommend the wood in the attic be tested for moisture, particularly your roof sheathing...it may already be pretty saturated and you may need to do some preventative things to keep it from getting fuzzy if it isn't already so.

Last edited by MoldBuster; 01-21-2007 at 03:39 PM.
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Old 01-22-2007, 07:12 PM   #12
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Originally Posted by MoldBuster View Post
Whoa! That sounds like a vapor trapping sandwich and may explain why you have condensation. You need to remove the plastic between the layers of insulation. With two layers of plastic, moisture can build up in the insulation layer in the middle and it becomes heavy and ineffective (cold). Typically, there should be one vapor barrier only...you have 4. Common practice when using batt insulation is to use faced bats on the bottom with the batt vapor barrier facing downwards and stapled to the joists and NO plastic vapor barrier. Then a second layer of UNFACED batt insulation. If you have installed plastic to the bottom side of the joists just under your T&G Oak, you should have used unfaced insulation (if you used faced insulation...you have 6 vapor barriers which HAS to be a record!) and it needs to fill the joist cavity all the way down to the top layer of the ceiling. Also, when you say you used plastic sheeting and "Bubble Wrap" between the bottom of the roof joists and your T&G Oak ...are you talking about a bubble radient barrier? Or are you talking bubble wrap as in wrapping something in it and shipping it? If you are talking radient barrier (proper radient barrier has two layers of bubble wrap sandwiching a layer of reflective foil in the middle, then it should have been the only vapor barrier installed and you should have tuck taped all the joints or the vapor barrier is ineffective. Using a second layer may trap moisture. If you are talking about pack it and ship it bubble wrap...

You also want to open up the attic ventilation again. If I understand you correctly...you installed vent chutes from the soffit vents all the way up to the top of the ridge vent? And then you installed plastic to the underside of the entire roof structure? This is incorrect. First off, there will be little to no airflow thru those spaces under the soffit vent chutes. Airflow thru a ridge vent system depends on a temperature differential and there won't be enough of one to set up much of an active airflow. Combine that with the plastic underneath and you may totally mold/rot your roof sheathing out. There should be one soffit chute installed at the soffit vent side and my strong opinion is that the plastic needs to go bye bye. The purpose of the soffit chute is to provide an airflow channel where the insulation meets the roofline to keep the insulation from plugging the ventilation. Assuming I understood what you did, your entire attic space has been closed off from ventilation. Also, I am thinking that plastic layer on top will trap moisture on the underside from temperature differences and it is going to drip down, land on the top insulation, drip down to the plastic layer and sit there getting stagnent and trying to find someplace to go. It will also run down the plastic and then down inside your walls if the roof pitch is high enough. This is a guaranteed recipe for mold and rot. You need to provide for airflow exchange thru your attic space. I spend a lot of time adding MORE airflow when we remediate moldy attics and end up opening soffit vents all the time that are plugged with blown in or had no soffit vent chutes installed (or they used those #$%#'ing cardboard chutes that rot and/or collapse). I usually recommend my clients add MORE airflow thru active vent fans (with a thermostat and a humidistat). If you want to put up a radient barrier in the attic to the underside of the roof joists, it is not a bad idea but the radient barrier needs to be the PERFORATED foil type (this is what I used in my home). At this point, I'd strongly recommend you hire a highly experienced home inspector to come out and consult with you. I am fairly certain they will tell you the same things I did. I'd also recommend the wood in the attic be tested for moisture, particularly your roof sheathing...it may already be pretty saturated and you may need to do some preventative things to keep it from getting fuzzy if it isn't already so.

Thank you for your suggestions, out goes the plastic.
Dan
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Old 01-31-2007, 10:54 AM   #13
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Cathedral Ceiling Sweats


Youre condesing on the inside of the ceiling?
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Old 02-20-2007, 10:13 PM   #14
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Check out the website - buildingscience.com and look at cold climate options. from there you might be able to find one that would suit you. Recently code officials in many states have revised their opinions on venting cathedral and flat roof systems. if your building does not have a 'water source' problem, like a wet basement, you may be able to change your setup.

It may be that the moisture is occuring because the surface of the sheetrock is very cold. Cold air might be flowing through the fiberglass at the base of the ceiling. You might want to install baffles to make the roof vent air go through the polystyrene vents. Some insulation contractors have IR cameras which would show cold spots. You can do the same with your hand.

On a recent addition I installed dense-pack cellulose in an unvented cathedral ceiling. It is performing about twice as well as fiberglass would primarily because air doesnt flow through it, like in fiberglass. Look at info from cellulose mfrs to verify this method.

good luck. ps the rules on vapor barriers and venting do change.
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Old 02-22-2007, 11:40 PM   #15
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Dan,
You might want to try out this website, http://www.buildingscienceconsulting...louisville.htm is a great resource for roof and wall assemblies that make sense, you should be able to find an illustrated drawing of a cathedral ceiling for your climate conditions.
You live in a mixed humid climate or the Department of Energy 4A & 3A regions and should design your roof and ceiling accordingly.

Good Luck

Slim

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