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What is the best means to reduce humidity in an attic if not using attic fans?

user-6955169 | Posted in Energy Efficiency and Durability on

Hello. I appreciate all the information about why attic fans are not beneficially for reducing heat in the home, but what about humidity? We just bought a home built in 1945 that had mold in the attic and we were told to add more attic fans to reduce humidity. What would be a better solution? Our climate in Maryland is very humid. Thank you for your advice.

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, can you tell us your name?

    High humidity in an attic is usually caused by air leaks in the ceiling of the top floor of your house. During winter months, humidity from this escaping air can condense on cold attic surfaces, leading to mold. So the first step is to seal the air leaks.

    Here is a link to an article that describes the work: Air Sealing an Attic.

  2. user-6955169 | | #2

    Thanks for your response. I understand the need to seal air leaks, and I appreciate the informative article. However, if the heat and humidity enter the attic through the vents during the summer and the air isn't being circulated, then that is a prime condition for mold. I've had mold growth on our drywall and cabinetry in our main living area simply by keeping the windows open and not using the AC during the summer. So without ventilation in a dark, warm, and moist attic, how will sealing air leaks prevent mold growth?

  3. GBA Editor
    Martin Holladay | | #3

    The main reason that most attics are dry (assuming there is no air leak from the interior) is that they are hot. Most attics are baked by the sun. An attic is an oven, and ovens are dry.

    If I enter an attic and it's moist and moldy, I immediately think, "This is odd. What's going on here?" As I said, the answer is almost always the same: There is an air leak that brings humid interior air (or air from a basement or crawl space) into the attic. Because if there wasn't this type of air leak, everything should be dry.

    There are a few exceptions to this rule, and the exceptions are in the Pacific Northwest, where it is damp and cloudy for months at a time. In that climate, you can get mold in an attic, just because the attic is vented, and there isn't much you can do about it.

  4. Norman Bunn | | #4

    What climate zone are you in? Also, how is the attic currently vented?

  5. GBA Editor
    Martin Holladay | | #5

    In the original question, Paul stated that he lives in Maryland. That is Climate Zone 4A.

  6. Norman Bunn | | #6

    Ah. Missed that.

    Still wonder if he has adequate venting at the roof and/or gables. If it is just soffits, then he is getting little, in any, circulation.

  7. Expert Member
    Malcolm Taylor | | #7

    It's probably worth noting that although the price we pay for living in the PNW is mold on our attic sheathing and north-facing walls, unless something else is at play the mold is superficial and shouldn't cause more than aesthetic problems.

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