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Community and Q&A

Summer condensation

user-1143609101 | Posted in General Questions on

Why am I getting condensation on my wood cathedral ceiling.  The air conditioning is running properly but the heat and humidity are very high outside. 90 degrees plus. At eye level the rooms are 71 degrees,  but up near the peak it’s at least 85 degrees.

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  1. Expert Member
    Akos | | #1

    Most likely the combination of two things.

    T&G ceiling generally are very leaky unless detailed properly before hand, stack pressure in the summer time moves hot air into the house through the ceiling. When this hot/humid air hits the cold T&G, it will condense.

    Second problem is lot of these T&G roofs are also tend to be unvented. During clear nights in the summer the roof surface can fall bellow outdoor temperature and you get condensation on the bottom of the sheathing. When the sun hits this condensation is drive out into the roof cavity without proper venting this has nowhere to go and drips down onto the T&G bellow.

    Both problems are fixable, neither one is easy and requires major work.

    1. user-1143609101 | | #2

      The space is vented next to the plywood roof sheathing, unless some of it got squashed when the wood underneath was put on. Funny thing is it happened both days at 4:00 in the afternoon. This never happened in the 30 years since it was built. I'm going to lower my thermostat to 72 and run a regular oscillating fan pointed up to mix the air. Do you think ceiling paddle fans would help?

      1. Expert Member
        Akos | | #3

        Cranking your AC up will most likely make this problem worst. You generally never want to set your AC bellow the outdoor dewpoint. My guess is with the current heat wave your outdoor dewpoint went pretty high which caused the issues.

        What you want to do set your AC higher and run a dehumidifier to make up for the loss in moisture removal. I find a house that is warmer but lower RH is much more comfortable than one that is overcooled.

        Once the outdoor dewpoint drops, you can set your AC back to normal.

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