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Getting heavy condensation on the inside of the exterior boards.

Adamkaravas | Posted in General Questions on

I’m in a 50s bungalow in southeast michigan that has a walk in closet built into one of the attics. The closet was recently gutted when my wife discovered mold on the drywall on the only exterior wall of the closet. The exterior wall was poorly insulated and I figured that’s why it was wet. I left it open for two weeks to dry out, which it did so I installed r-13 faced fiberglass insulation and left it for a week. I pulled back the insulation a week later to find the wall was soaked again. The exterior is aluminum siding on top of the old tile based siding a visual inspection did not reveal any leaks so I figure I’m dealing with an air issue that I want to solve before closing the wall up. I could always do a rubberized coating on the inside of the exterior wood boards but that won’t solve the moisture problem that would rot the boards it would just prevent interior moisture and mold. I’m looking for a solution and welcome any help or ideas. Thank you

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  1. wjrobinson | | #1

    Missing air barriers
    High moisture

    Lower your moisture loads
    Add air barriers

    Simple solution... Buy a froth pack and spray foam that one problem area. Great low cost fix for now.

  2. GBA Editor
    Martin Holladay | | #2

    Your interior air is relatively humid, and the sheathing boards are cold. If you don't have an air barrier that prevents your warm, humid interior air from contacting the cold sheathing boards, then you will have moisture accumulation (or frost) on the boards. Fiberglass batts are air-permeable; they don't stop the air from contacting the cold sheathing.

    There are several ways to attack the problem; you can use one approach or several.

    1. You should identify the sources of moisture in your house -- the usual culprits include a damp basement / crawl space or a humidifier -- and address these problems. Humid interiors are risky.

    2. You should choose a type of insulation that is impermeable to air; AJ's suggestion (using two-component spray polyurethane foam) is a good one.

    3. If you insist on using air-permeable insulation like fiberglass, you should (a) only install the insulation when the sheathing boards are dry, (b) do an impeccable job of installation, without any voids or compressed areas, and (c) immediately cover the insulation with a good air barrier -- for example, drywall installed according to the Airtight Drywall Approach.

    For more information on this problem, see Why Is This Sheathing Moldy?

  3. wjrobinson | | #3

    Martin, me thinks you get paid by the word and I don't.

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