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Community and Q&A

Attic ventilation?

user-6724719 | Posted in GBA Pro Help on

We just completed having a house in built NH in the the Upper Valley.  There is unfinished space above 3 car garage. The floor is insulated, but the walls and ceilings are just studs and rafters (except the wall connected to the main house, which is insulated). This unfinished space has multiple casement windows.  Because the eventual (5+ years from now) aim was to convert into mother-in-law quarters, there is no ventilation in this space, and the roof is a “hot” roof, and there are not eaves vents or vents elsewhere.  The space is hot in summer, freezing in winter.  Our attic in our old house has fans that turn on in hot weather. There are no such features in the this space.
Question 1: Can I leave the space unventilated? or will leaving it as constructed damage the structure (damage roof? or accumulate moisture? or other problems?).  I could leave the windows open, with casement windows a fair amount of rain would enter the space.
Question 2: If ventilation should be added, how would this best be accomplished.
Thanks you

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  1. Expert Member
    Dana Dorsett | | #1

    It may be worth cracking a window, but it probably won't really need it to remain structurally sound. Moisture is the enemy here more so than temperature. if the RH averages north of 70% during the shoulder seasons & summer mold can get started, so monitor the humidity (or just use your nose.) If necessary run a dehumidifer during the warmer months when it's consistently above 50F outside. Or keep a few windows just barely open if you notice the RH is creeping up. It-doesn't take much air exchange for the indoor humidity to track the outdoor humidity when there are no interior moisture sources.

  2. GBA Editor
    Martin Holladay | | #2

    You don't need ventilation, and (unlike Dana) I can't imagine that humidity will be a problem in this space.

    Here is a link to an article explaining why powered attic ventilators are a bad idea: "Fans in the Attic: Do They Help or Do They Hurt?"

  3. Expert Member
    Dana Dorsett | | #3

    I can IMAGINE the possibility of humidity being a problem in that space, but don't think it's likely. If the moisture content of everything in the space is low now, it will likely remain low, barring a roof leak or something.

    Humidity monitoring is cheap, if you're a person who might lose sleep over it.

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