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How do I go about dealing with moisture issues in wall cavities of old (1926) stucco home?

cnye | Posted in General Questions on

I recently embarked on a bathroom remodel. When we removed the old tub and surround there was considerable fungus and mold issues behind the surround on the northern exterior wall as well as fiberglass insulation. When we went to put the new tub in we had to remove a little more of the exterior wall and once again I found more mold and fungus, which prompted me to remove the whole northern exterior wall in the bathroom. There isn’t really a lot of rot, just some stuff that’s been there before the last remodel and wasn’t removed. I ordered Bora-Care with Mold Care to treat it and have been allowing the space to dry out. I have a few questions:

1.) I’ve read conflicting information about insulation. Some people say to leave the wall cavities empty for air movement (stucco is about an 1 inch thick on top of ship lap-tar paper was used in between but it has deteriorated). while others say to insulate.
What would you recommend?
I’m very concerned about this issue coming back and feel that the insulation added to or possibly created the issue.

2.) I haven’t been 100% sure that the moisture issue is just from the tub surround (didn’t have a vapor barrier underneath it) and bathroom moisture, it seems like something is coming from below or the exterior. The mold and fungus is on the ship lap and all the studs the whole span of the bathroom, but sheet rock was fine on the inside wall side.
Any ideas regarding this?
Could the vented dryer in this area be exacerbating this issue?

Thanks,
Corry

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Corry,
    You haven't told us your geographical location or climate zone. That information would be helpful.

    The moisture you describe could be coming from the exterior. (In other words, it could be rain entering the wall assembly due to a flashing problem.) Or it could be coming from the interior (especially if you live in a cold climate or if the tub had a defective tub surround).

    The clues to determining the source of the moisture can be seen in the rot patterns. Ideally, everything was carefully photographed at each stage of the demolition. If you didn't do that, we've lost crucial evidence, and we'll have to rely on your memory and description.

    In brief, this wall needs to be carefully detailed. The exterior needs to be examined for clues to the quality of the flashing job, especially if there are any penetrations (for example, porch railings).

    All rotten components of the wall need to be removed, and the wall needs to be air-sealed and insulated according to modern requirements. Then you need to install a tub surround that is waterproof.

  2. cnye | | #2

    Thanks for the reply.

    I live in the Pacific Northwest , close to the Canadian border. Temps range from 20's to 80's. We've been experiencing warm weather 48-75 in the last month.

    This is happening on the Northern side of the house where there aren't any issues with rain/water infiltration, exterior is all stucco with a cedar trim rail that sits on belly board. In 9 years of owning the home we've only had one storm that has come from the North, otherwise southerly winds/rain. The dryer does vent right in this area and there has been condensation when using on the exterior wall.

    The moisture patterns are coming from the sole plate and going up the wall cavities to the double top plate. Lots of growth where the studs meet the ship lap in the corners(a lot of the growth that was farther up cavities looked non-active, dried up, where at the bottom it was active) A few interesting things that I noticed was there wasn't action in the small wall cavities above the bathroom window, and limited issues in the interior wall of the surround.

    Since, I've had the wall open for the past few days it's completely dried out. I also know in the past I've had major issues with the roof leaking, which have been rectified (you can see the staining on the drywall at the ceiling in the attic.

    Thanks,

    Corry

  3. GBA Editor
    Martin Holladay | | #3

    Corry,
    Q. "Some people say to leave the wall cavities empty for air movement (stucco is about an 1 inch thick on top of ship lap-tar paper was used in between but it has deteriorated). While others say to insulate. What would you recommend?"

    A. I recommend that you insulate. Insulation will only be effective if you have a plan to reduce air leakage. What approach you'll take to reduce air leakage depends on the type of insulation you choose to install.

    Q. "I'm very concerned about this issue coming back and feel that the insulation added to or possibly created the issue."

    A. The insulation did not cause this issue. There are three possible moisture sources. Either (1) rain is leaking through defective flashing (you have told us that you are sure this isn't happening), or (2) Moist indoor air is entering your wall cavities through air leaks (a problem that can be solved by air sealing measures), or (3) a defective tub surround is allowing water from your tub or shower to enter the wall cavity.

    Q. "I haven't been 100% sure that the moisture issue is just from the tub surround (didn't have a vapor barrier underneath it) and bathroom moisture, it seems like something is coming from below or the exterior."

    A. You need to nail this down. In your original post, you wrote that "it seems like something [moisture] is coming from below or the exterior," but then in comment #2 you wrote, "there aren't any issues with rain/water infiltration." Both of these statements can't be true. Either there is water entry from the exterior or there isn't -- but you need to investigate that possibility thoroughly. Moisture entry "from below" would be unusual -- but it's technically possible, if you have a damp crawl space that communicates with your wall cavity.

    Q. "Could the vented dryer in this area be exacerbating this issue?"

    A. As long as the dryer is vented with solid duct (galvanized duct) and the seams of the duct have sheet-metal screws and the duct seams are sealed with foil tape, I don't think the dryer vent has anything to do with this.

  4. cnye | | #4

    Thanks Martin!

  5. Jon_R | | #5

    > air movement ... others say to insulate.

    Once you fix any bulk water issues, I'd do both: build a 3/8" air gap against the interior side of the ship lap and vent it (top and bottom) to the exterior (even a little helps). Then air seal and insulate.

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