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Community and Q&A

How do I correct condensation on my cathedral ceiling?

Jill Adams | Posted in General Questions on

I have lived in my house for twenty years and have never had a problem with condensation. About a year and a half ago I hired someone to make my house more energy efficient. He sealed leaks in the attic, and added blown cellulose insulation. He replaced the can lights with can lights designed to have insullation placed over them. At the time he did this work, airconditioning ducts ran through the attic. Shortly after that, I installed a geothermal unit and had the ductwork redone so that it is now in the crawl space. ( While I had central air before the geothermal unit, I didn’t have central heat until after that was installed).

Now I am getting visible condensation and mold on my cathedral ceiling in my living room. It has appeared for the first time this summer as I run the air conditioner. The living room extends out from the house. Part of the cathedral ceiling is a true cathedral with only a little space between it and the roof. Part is from an A frame that extends into theattic. The condensation is worse on the part of the ceiling that extends into the attic, so that there is space between the ceiling and the roof.

The air conditioning ducts that are no longer used remain in the attic with vents into the ceiling, although can’t tell that the condensation is spaced so that these vents are relevant. It is most extreme at the peak of the ceiling.

I have had a roofer look at it who did not think roof venting was an issue. How can I correct this and what kind of person should I be consulting to get it corrected? Thanks for any help you can give me.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Jill,
    If you are getting condensation on your ceiling, it means that those areas of the ceiling with condensation on them are the coldest surfaces in the room. Since this is happening during the summer when your air conditioner is on, you know that this is not a problem of exterior air. The only way your ceiling can be that cold is if an air-conditioning duct (or a seam in the duct) is leaking cold air, and the cold air is directed toward your ceiling.

    Someone needs to inspect your ductwork and, if necessary, perform a duct leakage test with a Duct Blaster.

  2. Jill Adams | | #2

    Further question: Thank you for your response. The air conditioning ducts are now in the crawl space with vents in the floor. The vents in the living room are quite some distance from the area that is getting the worst condensation. While there is still duct work in the attic, it is not being used and no cold air flows through the attic duct work. While I have no building knowledge, it seems counterintuitive that cold air ducts in the crawl space could be causing this. Am I mistaken?

    I should have mentioned that I live in climate zone 4A. (Quite hot and humid in the summer).

  3. TJ Elder | | #3

    I'll take a guess that this condensation is happening on the warm side, meaning that hot humid air inside the attic is condensing against the back face of the ceiling drywall. If there's a poly vapor barrier behind the drywall, that might explain the problem. If not, this is surprising because even in a very hot and humid climate it's normally possible for moisture to diffuse through the drywall without resulting in visible wetness. The reason extra insulation could cause this problem is that it separates the ceiling from the attic heat, so the drywall is colder.

    If my guess is accurate then the moisture might dissipate just by raising the thermostat setting, so it's not so chilly inside.

  4. David Bourbon | | #4

    It's likely that the ceiling surfaces adjacent to the attic are now cooler because of the new insulation. That the area of the ceiling under the roof has less condensation would signify a temperature difference. By relocating the air source from the ceiling to the floor, there is probably not enough air circulating in the peak area to discourage condensation. You might bring in some portable fans to increase the air circulation and test this.

  5. Robert Hronek | | #5

    The dew or condensation point is a moving target. As the air get dryer the dew point is a colder temp. As the humidity goes up the dew point is a warmer temp.

    Inside a house with air conditioning the air is dry and has a low dew point. If you look at air ducts in a basement they do not sweat when the ac is running and the duct work nearest the ac is the low 60s or in the 50s. If there was an air leak of humid outdoor air then you could see sweating in small areas.

    Depending on your location and current conditions outside could be very humid with a dew point much higher than inside. The dew point could be well into the 70's. But attic temps should be well above the dew point.

    Now if there is a warm moist exterior air coming into contact with a cold surface then you could get some condensation. I would look for areas where warm moist air could be geting behind the insualtion and reaching a cool surface. Where the old duct disconnected but air is still able to flow in to them from the house?

    I would say that you need to find why there is a combination of low temp and high humidity.

    I would check attic venting again. See if insulation got blown in to the eves. Are the bathrooms and/or kitchen vented in to the attic?

  6. Expert Member
    Michael Maines | | #6

    Jill, this part of your description is confusing but I think it holds the key to your problem:

    "...Part is from an A frame that extends into theattic. The condensation is worse on the part of the ceiling that extends into the attic, so that there is space between the ceiling and the roof.

    The air conditioning ducts that are no longer used remain in the attic with vents into the ceiling, although can't tell that the condensation is spaced so that these vents are relevant."

    Could you elaborate on what this looks like?

  7. John Brooks | | #7

    an interior and an exterior photo might be "helpful"

  8. David Bourbon | | #8

    "The air conditioning ducts that are no longer used remain in the attic with vents into the ceiling, although can't tell that the condensation is spaced so that these vents are relevant."

    If any part of the ducts is open to the attic, or if there are gaps, cracks, or other openings in them, the humid air is entering the room through the vents and condensing on the colder surface of the ceiling. Moisture migrates from warm areas to colder areas.

    The solution may be to remove the vents, fill and patch the openings in the ceiling, and fill the gaps in the insulation on the attic side. Good luck!

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