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Climate Zone 3-strategy for venting or not venting a small attic kneewall space?

JGood2170 | Posted in GBA Pro Help on

Climate Zone 3. I have a Finished Room of the Garage (FROG) with kneewalls that has wood paneling on the finished side. The paneling started to show signs of moisture issues. I removed the paneling and found no mold in the space but elevated moisture (22%). R13 insulation with vapor retarder on warm on winter side is present. There is not much room between the kneewall and the exterior wall of the reverse A. Essentially a double 2×4 wall is it. This area is closed off to the rest of the vented attic due to the sloped ceiling of the finished room being tight to the roof rafters (insulation present but not room to vent to ridge vent). There is one 16×8 soffit vent in the closed off kneewall space. The question is…should I close of the soffit vent and pack the space with insulation? Or add a couple more soffit vents to hopefully better circulate air? In the humid climate if feel closing it off is the better solution since its such a small space but unsure. Right not it seems to just be letting hot humid air in through the one soffit vent.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    J. Good,
    Your instincts are correct. It sounds as if the vent is introducing hot, humid air to the area behind your kneewall. If the room above the garage is air-conditioned -- I'm guessing it is -- the moisture is probably condensing or accumulating on the back side of the wall paneling.

    Sealing up the soffit vents would help, and so would removing the warm-in-winter-side vapor retarder (depending on what type of material it is). If the vapor retarder is polyethylene, it's part of the problem. If the vapor retarder is kraft paper facing on the insulation, it's less problematic.

  2. GBA Editor
    Martin Holladay | | #2

    J. Good,
    You might want to read this article: “Two Ways to Insulate Attic Kneewalls.”

  3. JGood2170 | | #3

    Thanks Martin.

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