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Insulation/Mold

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Joey J, Mar 4, 2013.

  1. Joey J

    Joey J New Member

    Joined:
    Feb 11, 2013
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    Putting in a Class A chimney where a ZC fireplace used to be. It's enclosed in a OSB board wood chase exterior of the house that runs two stories up and has a fire stop between the floors. The house wall has been insulated the whole way up except where the ZC fireplace was installed. The rest of the 3 wall of the chase are not insulated. The chase faces North. The house is about 13 years old. I live in the mountains of western South Carolina. Temps do dip into the low 20's. The problem: Once I gained entrance to the chase I notice I had a what I would call mold. Not much below the fire stop and a little more above the fire stop. Mostly the effected area is on some of the side walls of the chase. It's only in a few spots at this point. Let me also say that there is no air circulation from the fire stop down. ( I guess that's why they call it a fire stop. ) From the fire stop up there doesn't seem to be any opening either as the old air cooled chimney looks to be sealed on it's outer shell going though the top of the chase cap. I plan on getting rid of the mold that is there by spraying bleach on it and than applying "KILLS" lacquer to the effected area. Did the ZC fireplace contribute to this situation being that the insert was in "the wall" and had no insulation around it. (stove wasn't used very much) The wood stove will sit outside the chase. Now my question is do I try to vent this chase somehow? Do I insulated the whole thing? Do I just leave it alone? Advice please.

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  2. begreen

    begreen Mooderator Staff Member

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    Hard to say when the mold occurred, it might have been during summer. Perhaps it's because the chase retained overnight coolness and then sweat during hot, humid summer days? This is pretty typical in some crawl spaces for the same reason.
  3. Joful

    Joful Minister of Fire

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    Does the chase extend down to earth? What sort of vapor barrier do you have at the bottom? This is common when you have earth contact, which provides both moisture and cooling, and no ventilation. The solutions are usually vapor barrier, applied heat, and/or ventilation.
  4. begreen

    begreen Mooderator Staff Member

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    I think he said the mold only showed up above the sealed firestop. Usually that is at the first floor ceiling level.
  5. Joey J

    Joey J New Member

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    The chase is on a crawl space and is about 3 feet off the ground. It's also insulated underneath.There is mold at each level but more after the fire stop. I didn't see any on the " inner " wall of the house which is insulated and no evidence on the outside of the chase itself. I have no mold anywhere else in the house as far as I can tell. Ventilation was mentioned how would this be done?
  6. Joful

    Joful Minister of Fire

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    Yeah, that's a little unusual. I don't think the fact that the moisture is condensing there precludes the possibility that it could be coming from the ground, though. If there's mold, there's moisture... and it must be coming from somewhere. The chase sitting on footer with a gravel fill and no vapor barrier would be a common source.

    You have me stumped! Any possibility the moisture is coming from the outdoor air in summer, and the chase is being kept cool by contact with your exterior wall? I assume that in winter time, the chase is almost always kept warm by the chimney, so condensation and mold should not be an issue during winter.
  7. Joey J

    Joey J New Member

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    Living in the south we do run the A/C most every day so the exterior walls may be doing it but it is insulated. Maybe a plastic vapor sheild over the insulation on the exterior wall may help and one beneath the floor? I didn't see any on the far wall just the sides of the chase. Being a transplant from the New York area I haven't seen this problem before.

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