# Condensation issue with a vaulted ceiling and skylights



## Sir Mixalot (Jan 6, 2008)

Definitely not from the a roof or skylight leaking. 
But from condensation issues with the vaulted ceiling and skylights. There are no signs of the condensation running down from the skylight on the interior side of the drywall. Seems like there is plenty of ventilation in the attic and the back of the drywall is dry and never been wet by the looks of it. So the condensation is forming on the interior side of the vaulted ceiling. 


Anyone have any thoughts on why this is happening?


Ps. I think I know why it's happening. But it's a weird one.


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## Tom Struble (Mar 2, 2007)

condensation may be forming on the backside of the metal flashing,little paper or s.a. will cure it


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## Sir Mixalot (Jan 6, 2008)

Tom Struble said:


> condensation may be forming on the backside of the metal flashing,little paper or s.a. will cure it


Tom, the skylight is around 6' to 8' deep inside the house and there is no sign of moisture running down the front or back of the drywall that is in the skylight. :no:


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## Tom Struble (Mar 2, 2007)

so your thinking blowing in from the ridge vent?


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## Tom Struble (Mar 2, 2007)

could be a reverse lap at the head flashing


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## Sir Mixalot (Jan 6, 2008)

Tom Struble said:


> so your thinking blowing in from the ridge vent?


:no:



Tom Struble said:


> could be a reverse lap at the head flashing


I don't see any evidence of water anywhere on the roof decking or anyplace in the attic.


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## Tom Struble (Mar 2, 2007)

ok so the high hats?what? don't make me keep guessing..cause i will:whistling


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## hdavis (Feb 14, 2012)

AC duct making a cold spot on the drywall, condenses during high humidity.


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## iDAHOchris (Feb 11, 2012)

broken hood vent in kitchen?? Hard to say Florida and Idaho are total opposites


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## Tom Struble (Mar 2, 2007)

hdavis said:


> AC duct making a cold spot on the drywall, condenses during high humidity.


ahh..


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## Snobnd (Jul 1, 2008)

Looks like the air conditioners pumping in moist cool air instead of dry cool air ,maybe a dehumidifier?


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## hdavis (Feb 14, 2012)

iDAHOchris said:


> broken hood vent in kitchen?? Hard to say Florida and Idaho are total opposites


Helps to put on some sunscreen and imagine it's 80F, 80%RH...


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## Sir Mixalot (Jan 6, 2008)

hdavis said:


> Helps to put on some sunscreen and imagine it's 80F, 80%RH...


:laughing:


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## loneframer (Feb 13, 2009)

I've seen something similar caused by insulation being packed tightly around the skylight, choking off any air movement. Inside of the house is cool, attic is hot and humid. Moisture condenses on the warm side of a cold surface, in this case, metal corner bead and you've got a problem.


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## Sir Mixalot (Jan 6, 2008)

When I pulled the corner bead off, it wasn't even rusted on the inside. Only on the outside surface of it and the drywall had no water damage at all. :no: 
The HO had been spraying a strong bleach solution on those areas for awhile, trying to make the discoloration on the ceiling go away. 
Basically it's just a big surface stain and corrosion of the metal bead. Although the condensation issue does still exsist. :blink:


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## icerock drywall (Aug 16, 2012)

sky lights are to close to the ridge vent ...move skylight down 2 feet and this will not happen


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## Paulie (Feb 11, 2009)

Does the other skylight I see in a roof shot do that?


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## loneframer (Feb 13, 2009)

The skylight opening prevents airflow, rendering the ridge vent useless above each skylight.

The opening is headed off, insulation in place and regardless of whether there is proper vent chutes installed, there is no intake air.

I'm not surprised that the bead isn't rusted on the back, due to the fact that it's zinc plated, or essentially, galvanized. The bleach, typically sodium based,(salt), will corrode the zinc, explaining the rusting from the face. Nonetheless, there is moisture where there is mold. I'd bet the drywall shows high levels of moisture when the condensation is present and my guess is, it's elevated as far as the limits of the staining.

Something else to consider though is whether the AC unit is oversized, which will prevent the moisture in the air from being removed effectively during cooling.


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## ScipioAfricanus (Sep 13, 2008)

It looks to me that the roof and ceiling systems are scissors-trussed, so the ridge venting would not be a cause.
I am going with what HDavis said, the A/C is pumping cool air at those locations and as the warmer interior air is rising, it is condensing on the underside of the drywall at the high end of the skylights.

Well, do you already know what the cause is SirMixalot and you are just teasing us?

Andy.


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## Tinstaafl (Jan 6, 2008)

Andy et al, another piece of the puzzle that Paul didn't mention here is that the HO says this only developed in the last 2-3 years. No idea how old the home actually is.


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## Sir Mixalot (Jan 6, 2008)

loneframer said:


> I've seen something similar caused by insulation being packed tightly around the skylight, choking off any air movement. Inside of the house is cool, attic is hot and humid. Moisture condenses on the warm side of a cold surface, in this case, metal corner bead and you've got a problem.


The insulation isn't packed tight at all. It's just placed in that area and easily pulls back. 
I think it does have something to those ac vents at the top of the vaulted ceiling though. :thumbsup:


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## Sir Mixalot (Jan 6, 2008)

Paulie said:


> Does the other skylight I see in a roof shot do that?


No it's fine. Just the two in the other photos have the issues. :thumbsup:


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## Sir Mixalot (Jan 6, 2008)

loneframer said:


> The skylight opening prevents airflow, rendering the ridge vent useless above each skylight.
> 
> The opening is headed off, insulation in place and regardless of whether there is proper vent chutes installed, there is no intake air.
> 
> ...


All very valid points Riz. :thumbsup:
I do think the skylights are definitely blocking some of the airflow in the attic in those areas. The only thing is that, this problem just started in the last 2 to 3 years. The house is probably around 15 years old. So, I would think this issue would have reared it's ugly head sooner. :blink:


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## loneframer (Feb 13, 2009)

Sir Mixalot said:


> The insulation isn't packed tight at all. It's just placed in that area and easily pulls back.
> I think it does have something to those ac vents at the top of the vaulted ceiling though. :thumbsup:


I totally agree that it's converging of cool air and warm air that causes the condensation. It's the moisture that enables it.

If it's something that came on out of the blue, you need to go through a process of elimination. What changed?

Were there trees removed that would have shaded the roof, lowering heat gain in the attic?

New siding/soffits installed that would hinder airflow?

AC system modified or upgraded that would change the cooling characteristics within the home?

Darker roof shingles installed that would increase temps in the attic?

Change in cooking habits that might increase humidity within the home?

Exhaust fan in bathroom(s) improperly vented or clogged? I've seen birds nesting inside the ducting.

Clogged dryer vent, or possibly disconnected or loosely connected?

Unusually damp cooling season?

Unusually warm cooling season?

Attic fans that aren't functioning?


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## Sir Mixalot (Jan 6, 2008)

ScipioAfricanus said:


> I am going with what HDavis said, the A/C is pumping cool air at those locations and as the warmer interior air is rising, it is condensing on the underside of the drywall at the high end of the skylights.
> 
> Well, do you already know what the cause is SirMixalot and you are just teasing us?
> 
> Andy.


Yes, I think that the ac is blowing cold air in those areas and causing the cool air and the hot air to condensate. 
After being at the home and looking everything over. That was my conclusion too. Then as I was removing the failing drywall tape from the vault, I noticed that it had a few dirty spots on the backside of the tape and a few holes in the center. Especially right in front of the skylights. It got me thinking that hot air was escaping from the attic at the very center of the vaulted ceiling drywall tape and was running into the cold air from the ac vents causing the condensation issue on the interior side of the ceiling near the two skylights. 
It sounds crazy. But, I think it has alot to do with the bad tape joint at the vault.


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## Sir Mixalot (Jan 6, 2008)

loneframer said:


> I totally agree that it's converging of cool air and warm air that causes the condensation. It's the moisture that enables it.
> 
> If it's something that came on out of the blue, you need to go through a process of elimination. What changed?
> 
> ...


You're good Riz. :thumbup:


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## loneframer (Feb 13, 2009)

New AC system sounds suspect...

If the older system was properly sized, or slightly undersized, it would remove moisture more effectively than a unit with a higher cooling capacity.

Cooling the air too quickly, without adequately removing humidity will definitely cause condensation issues withing the home.


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## hdavis (Feb 14, 2012)

A convection current is being set up between the skylight and the duct due to the loose insulation install. Dense pack, foam, etc would prevent this.

Duct R values can degrade, which would make the problem worse. A hotter attic would actually help prevent betting the skylight area too cold.

Just sticking to basics (assuming no one messed with the laid in insulation), either the duct insulation has degraded some, or the temp of the air moving through the duct has gone down, or the room RH has gone up. As much sense as it makes, it still seems squishy to me. 

Those bays at the skylights only start cooling off when the AC runs, so the temp drop from the AC and how long it runs pretty much determines how cold the surface is going to get. A lot of the newer AC units have at least a 2 speed fan. The unit runs more efficiently sometimes on the low speed, but those bays are going to get colder than ever due to the longer run time. Even if the room RH is the same as it always was, you can now get condensation where you never had it before. 

There are a lot of factors that come into play, but in terms of the major ones that have changed, I'm guessing it's the AC change, and I bet it has at least a 2 speed fan.


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## Sir Mixalot (Jan 6, 2008)

loneframer said:


> I totally agree that it's converging of cool air and warm air that causes the condensation. It's the moisture that enables it.
> 
> If it's something that came on out of the blue, you need to go through a process of elimination. What changed?
> 
> ...


Thanks for all of the great feedback everyone! :thumbup:
I talked to the HO and she said the new ac is bigger then the old one.
The new roof shingles are lighter then the old ones.
Here's a few photos from the attic view of the skylights and surronding area:


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## hdavis (Feb 14, 2012)

That looks different from what I expected. The bigger AC is a good clue, but the question of why that area of the skylight is the coolest part of the ceiling (at least at some point in the day) is a puzzle. Maybe night time cool off?


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## loneframer (Feb 13, 2009)

Off topic possibly, but what's the deal with the discontinuous reflective vapor barrier fastened all willy-nilly to the underside of the rafters? Is that common practice?

I also am skeptical of the insulating around the skylight tunnels. Seems like a lot of open gaps in the vapor barrier and insulation for thermal/moisture exchange to take place.


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## thom (Nov 3, 2006)

Does this seem to happen in the summer or winter months?

Do you have a heating season? If so, and if the condensation happens during the heating season, the joint could be cool and condensing inside air.


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## Sir Mixalot (Jan 6, 2008)

loneframer said:


> Off topic possibly, but what's the deal with the discontinuous reflective vapor barrier fastened all willy-nilly to the underside of the rafters? Is that common practice?
> 
> I also am skeptical of the insulating around the skylight tunnels. Seems like a lot of open gaps in the vapor barrier and insulation for thermal/moisture exchange to take place.


Yeah Lone, I'm not sure about why the reflective barrier is like that. And as for the insulation around the skylight, I think the HO hubby might not have put it back like it was before he showed other contractors the area. 
Really though, I'm thinking it has something to do with the new bigger ac.


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## Sir Mixalot (Jan 6, 2008)

thom said:


> Does this seem to happen in the summer or winter months?


I'm not sure. What I do know, is those areas on the interior had no condensation what so ever on them from the time I got there, to the time I left (5 day's). :no:


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## loneframer (Feb 13, 2009)

Sir Mixalot said:


> Yeah Lone, I'm not sure about why the reflective barrier is like that. And as for the insulation around the skylight, I think the HO hubby might not have put it back like it was before he showed other contractors the area.
> Really though, I'm thinking it has something to do with the new bigger ac.


I agree. I've heard it from trusted pros, time and time again, it's better to be slightly undersized than to be oversized with AC.

In order to properly size a unit, there are many factors involved beyond cubic footage/tonnage.


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## hdavis (Feb 14, 2012)

Sir Mixalot said:


> Yeah Lone, I'm not sure about why the reflective barrier is like that.


Relatively cheap way top get a 20-40 degree drop in attic temps on a hot day (cold days as well). Usually stapled to the underside of rafters and cut out around vent pipes, skylights, etc.

It can also modify the attic ventilation airflow. If the house uses eave vents and ridge vents, the air tends to run from the eave up through the channel formed by the barrier and rafters, and straight out the ridge vent. In terms of moisture removal, it can wind up forming an impermeable moisture barrier for the conditioned space. I've only used the stuff down south in heavy AC use, light heating use, and I left a pretty good gap at the ridge (like 2 or 3 feet) so there still would be effective moisture removal from the structure.


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## CompleteW&D (May 28, 2011)

LoneFramer nailed it Paul. The other issues I see are those supply air ducts right in the middle of the ceiling. It throws cold air right down to the floor and all of the ambient heat (and moisture) stagnate right up at the ceiling. Those supply ducts should be lower in the room with return air being pulled from a side wall as high as possible, to pull the heat and humidity OFF of that cathedral ceiling.

I would suggest they take up their issues with and experienced HVAC guy and correct their airflow and moisture problems first.

Of course, it could be job security because you'll need to keep going back and fixing the same problem over and over again until they do. :whistling


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## CompleteW&D (May 28, 2011)

loneframer said:


> I agree. I've heard it from trusted pros, time and time again, it's better to be slightly undersized than to be oversized with AC.
> 
> In order to properly size a unit, there are many factors involved beyond cubic footage/tonnage.


You are EXACTLY right. I spent several years selling residential HVAC and I can't tell you how many times a HO would say "I want to go with a bigger AC unit." 

99 percent of the time, I found airflow issues that were the cause of the lack of comfort rather than the size of the AC being incorrect. When I fixed those, their comfort and efficiency increased dramatically.


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## madmax718 (Dec 7, 2012)

Actually.. since its winter.. Can I get a temp reading? 

Im going to go against the grain on this. If the AC is pumping out cool air, even if it was mixing, condensation usually doesn't form on the hot side of things- its usually the cool side of things. (like shower steam on a window)- The cold side condensates. 

If as described, you'd have to have the AC vent blowing against the area- enough so that it cools the metal enough to cause condensation. That also seems a little unlikely, given the height of the ceiling, the cold air would drop, while the hot moist air stays on top. And it appears that the same condition exists on both skylights.. even though there is only one vent.

Im just curious if this is more of a problem in the summer or winter. I'd speculate its winter.


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## Sir Mixalot (Jan 6, 2008)

madmax718 said:


> Actually.. since its winter.. Can I get a temp reading?
> 
> Im going to go against the grain on this. If the AC is pumping out cool air, even if it was mixing, condensation usually doesn't form on the hot side of things- its usually the cool side of things. (like shower steam on a window)- The cold side condensates.
> 
> ...


I'm not sure if it's worse during the Winter or Summer. My guess would be Summer. Simply because those area were completely dry the whole time I was there last week. But then again, it was in the 80's all week. So it's hard to say.

Also, there are two ac/heat vents near the skylights.


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