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Community and Q&A

Mold & termite/wood rot in 1920’s house

McKennaHouse | Posted in General Questions on

Climate zone 4A. Hot and humid in the summer and cold in the winter.

The house itself was built in 1920, on top of a rubble foundation built sometime in the 1800’s as a barn.

We removed baseboards and drywall on one full wall of the house and discovered what looks like either severe wood rot or termite damage. The back of the drywall had a sprinkling of black dots but not too bad. Not sure if it was mold or dirt.

The opposite wall, which we started to remove yesterday, doesn’t seem to have the bad wood rot/termite damage to the studs and beams, but it does have pretty significant mold. Additionally, the drywall seemed pretty moist in places.

After we finish removing all the drywall, (somehow) get the mold cleaned up, address whatever is causing the moisture, and replace the all rotted beams and studs –

How to proceed with insulation/vapor barrier to prevent this happening again?

The walls are 1) drywall, 2) cavity, 3) exterior wood (like shiplap but much wider), 4) cedar shingles.

Will a vapor barrier make things worse, or better? I read that insulation on the exterior is ideal but we can’t afford to remove the cedar shingles to access the exterior wall. Unless we do it carefully, save them, and then reattach?

A very few bays had pink fiberglass insulation, which of course was black and moldy. Is rigid foam between the drywall and exterior wall ok or will that cause mold too?

Want to avoid spray foam bc of toxicity.

Thank you so much!

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  1. Expert Member
    BILL WICHERS | | #1

    If you can post pics, we can maybe help identify if this is an "all mold" or "partially termite" problem. If you have a termite issue, you need to address that seperately from the moisture issue, although termites do do better in moist enviornments, so keeping the cavity dry will help to deter them somewhat.

    Since you think there might have been termite activity, I'm going to assume you're seeing most of the damage in the lower portion of the wall, nearer the foundation. That makes me think you may need to think about adding a capillary break, since mositure may be wicking up from the foundation, keeping the lower parts of the framing moist. That's a problem that will lead to rot, and will also be ideal for termites.

    Did the fiberglass have a kraft paper facing (which is a vapor retarder)? Was it installed correctly, with the facer on the "warm in winter" side (usually the interior in heating dominated climates)? I would try doing the usual air sealing of the exterior sheathing as well as you can from the accessible interior (assuming you have all the walls open), then insulate with batts, then use a smart vapor RETARDER (Membrain, Intello, etc.) on the interior, which should help. A vapor BARRIER (polyethylene) is likely to make the problem worse, and I would avoid installing one.

    There is no need to consider spray foam here, since it really doesn't offer any benefits for you in a wall.

    Do you run high indoor humidity levels in the winter? That's a fancy way to say "are you running a humidifier in the winter?" If you are, that's also part of your problem, since you're putting additional moisture into the air. Ideally you want to keep moisture levels low, although for health reasons I like to try for around 40% -- too wet is bad for the structure, too dry is bad for the occupants.

    Also, check if you have any signs of bulk water intrusion, which is usually caused by deteriorated, incorrect, or outright missing flashing details on the exterior. Roof problems (notably ice damming) can also contribute to water getting into the walls.


  2. McKennaHouse | | #2

    Hi Bill, thank you! I will take and post pics later today.

    Yes, most of the damage is in the lower part of the wall, though some of the studs (it's old timber, not sure if they're called studs but the "vertical beams") are rotted to pretty high up.

    After reading the Joe L. article about his rubble foundation house, I very much wanted to jack up the sill to insert a capillary break. 2 things have put that on the back burner for now: 1) seeing a few comments on here that maybe stone doesn't wick moisture as badly as concrete does (though maybe that's not the case given this damage). 2) We are planning to have the whole house lifted in a few years, as the top of the foundation is currently a few feet below grade in the front (a few inches below grade on another side / remaining 2 sides are fortunately above grade as foundation was built into a hill).

    Original thinking before we knew how bad the wood damage was, hang on till the house is lifted, then at that time replace the sill plate/rim joists as needed, and install capillary barrier. We will be getting a better look at the sill/rim today and I'll post what is found. Waiting may not be an option anymore?

    The few batts of fiberglass that were present by the front door did have kraft paper backing but it faced the exterior.


    1) air seal the exterior wall as much as possible from the inside
    2) install fiberglass with the kraft paper facing the interior
    3) install a smart vapor retarder, not barrier
    4) then replace drywall?

    We haven't lived in the house yet together, but it does have steam radiators and I've seen them release actual steam into the room periodically when in use. Maybe that was contributing to the humidity.

    I'd love to switch to a different heating source bc the boiler has a chimney that is right in the way of a planned fireplace, and also the house smells of gas every time the boiler comes on, and I'm pretty sure there's a carbon monoxide issue since the boiler, open flame water heater, and gas clothes dryer are all in a tiny room in the basement with no extra air source. Added to the gas range with no hood, gas oven, and gas fired wood burning fireplace, I can't imagine it's healthy. Hoping we can replace the existing air conditioner with a heat pump ac, use the existing ductwork for heat for now, and eventually get rid of the ductwork which takes up a lot of space, and switch to mini splits.

    Oh - speaking of ductwork, the drywall removal revealed there was a lot of black mold around where some exposed ductwork entered the ceiling in the kitchen. Do you think the ducts not being insulated could cause condensation and then mold in the walls?


    5) get a dehumidifer for the house (in addition the the basement one)


    6) have the roof inspected and fix any flashing issues.

    Thank you so much for your advice!!! This is invaluable.

  3. Expert Member
    DCcontrarian | | #3

    My guess is the problem is water infiltration, either leaking siding or splashing back from the ground. I'd eliminate that as a possibility before looking at things like interior humidity.

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