Kneewall ventilation
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  1. #1
    Should a sealed kneewall area of a cape be ventilated? The underside of the roof deck and side walls are sealed with icynene foam so there is no interaction with the outside air, but also minimal with the inside given doors to the area and maybe leakage around outlets, etc.

  2. #2
    Join Date
    Dec 2002
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    in a house, Appomattox, Va.
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    That would defeat the purpose of insulating under the roof deck. Icynene gives very good airsealing, and cutting in holes could allow lots of leakage into conditioned areas as well as knewall, not to mention increased heat loss/gain. Kneewalls are difficult to seal and insulate well, so its better to seal at exterior of house

    Do your closets have vents or ventalation? Same difference. You could add in transfer grills to conditioned if its an issue for you.
    Col 3:23


    questions asked, answers received, ignorance abated

  3. #3
    Join Date
    Apr 2004
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    7,680
    I think they should be ventilated like any other attic space. Those styrofoam fomes that make a "chute" for air to rise up along the roof work well provided the upper space is well ventilated as are the soffits.

  4. #4
    Join Date
    Jul 2004
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    midwest
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    You need to treat this area as a conditioned space. With this type of insulation there is no reason to vent the space behind the knee walls and it would defeat the purpose of the insulation you used.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Originally posted by newhomeboston
    Should a sealed kneewall area of a cape be ventilated? The underside of the roof deck and side walls are sealed with icynene foam so there is no interaction with the outside air, but also minimal with the inside given doors to the area and maybe leakage around outlets, etc.
    Back to your moisture problem on the second floor, high dew point air on the back side of an uninsulated kneewall will condense on the cooled drywall and move into the living space. My guess is that the air is dry because of the attic/wall foam. It's worth measuring the temp/rh on the back side of the wall. Radio Shack has a remote meter that transmits reading to a main meter. Cost fifty-three for both. If moisture is penetrating the attic, high humidity could be expected in 2nd floor. TB

  6. #6
    I've already checked and compared the kneewall humidity to the interior of the second floor...it is a little, slightly more humid (couple percent RH) and also a little warmer during the day than the "inside". Generally very similar conditions. The comparison to a closet makes sense. I was just wondering if stagnant air can cause any problems since I never plan to go in there.

    Thanks guys.


  7. #7
    interestingly, I've been running a dehumidifier non-stop upstairs to control humidity while things get figured out...the kneewalls hit 80 degrees today and 64%RH while the inside was in the mid-70's and 55%RH tops...not sure why a difference would appear now.

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,231
    Outside air must be leaking into the area or there is a moisture source nearby. ventilating in more outside humidity will not help this problem. TB

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