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I have mold in my attic. I have a mold remediation company that is going to come out and fix it but they will only warranty the work if the underlying issue is resolved.

The roof sheathing is at 100% moisture for most of my attic. There is also slight moisture on the top of the insulation. Roof is 4 years old. Roofer came back out and said it's not leaking as that wouldn't make sense that the entire roof sheathing is moist. Roof has open soffits and ridge vent. Clearly there is too much moisture up there.

There is one bathroom vent that runs through the attic and out the gable on the side of the house, originally it ran into the soffit but I changed that so the moisture doesn't get pulled back in.

Outside of the whole roof being bad, what would cause the sheathing to be so moist? How can I fix this moisture issue so the mold doesn't come back?

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  • Are you venting combustion exhaust (which includes water vapor) inside the house? Humidity condensing on the cold sheathing seems most likely given the new roof.
    – popham
    Commented Dec 28, 2023 at 22:37
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    Either your ventilation(soffits and/or ridge vent) is blocked or your roof is leaking. The other choice is you are in a 100% humidly location. This is assuming you do not have insulation on the roof deck/sheeting
    – crip659
    Commented Dec 28, 2023 at 22:37
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    I don't think there is any combustion exhaust venting in the house. Everything seems to be vented outside properly including both bathroom vents and the dryer. I did just watch videos about looking for and sealing entries into the attic including around cabling/wiring. I did mean to add the house is in NH. No AC, baseboard heating so no airflow inside the house. I can see light on the soffits and ridge vent so it seems like they are not blocked. No insulation on sheathing, just on the floor of the attic.
    – anonjeeper
    Commented Dec 28, 2023 at 23:13
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    Does not make sense. Your attic should be dry with what you say. Either your mold(if not tested) is something else(dirt/ink stains) plus the moisture test is wrong, or you have a source of moisture. Do you have any water supply pipes in the attic? Usually a very bad idea in NH.
    – crip659
    Commented Dec 29, 2023 at 0:17
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    Just to confirm, you don't have insulation against the roof sheathing, correct? I'm assuming this is a finished ceiling with insulation, then your open ventilated attic space with gable, soffit, and ridge vents, and above that is open sheathing. If that's not correct please advise.
    – KMJ
    Commented Dec 29, 2023 at 17:04

1 Answer 1

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Not a solution, but rather an investigative suggestion.

You need to monitor the temperature, humidity, and dew point (the critical parameter here) in your attic over a period of time. Such sensors are available from companies such as Govee (not a product endorsement) for around $15. You just set this device in your attic (or other space) and it logs temperature, humidity, & dew point over time. You can then access this log remotely using Blue Tooth and an app on your cell phone.

Most attics in humid climates probably have some moisture condensation in them when the temperature of the roof or other surface drops below the dew point. But with proper ventilation, this moisture should evaporate when the dew point drops (rising temperature or dropping humidity).

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  • I purchased a 2 pack. Hopefully this can provide some info. Thanks!
    – anonjeeper
    Commented Dec 30, 2023 at 1:42

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