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During my latest foray into the attic, I discovered that my bathroom exhaust fans vent directly into the attic. I'm worried about moisture buildup and I'm considering routing the exhaust to an external vent. How major of an issue is this, and which type of vent is best?

From my perspective, a soffit vent is going to be easier to do and doesn't have the potential to allow rain to leak into my attic. Is there any strong argument for a roof vent?

I found this article explaining a basic how-to of each procedure, but it doesn't give any pros/cons for each one.

Doresoom
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2 Answers2

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Soffit

Pros

  • Vent easier to install
  • In heavy snow areas, not likely to be blocked

Cons

  • Soffits are designed for intake, so it's possible the air will be sucked back into the attic
  • Moist air can collect under the soffit

Roof

Pros

  • Heat and moisture want to rise
  • Keeps moisture away from walls, windows, siding

Cons

  • Can be blocked with heavy snow
  • More difficult install

I don't think it's that difficult to install a roof vent - this is a pretty good video

Steve Jackson
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The natural flow of air in an attic is going to be pulling air in through the soffit vents and out through the roof vents/ridge vent.

The problem I see with exausting the air through a soffit vent is that the natural flow is going to tend to pull that moist air right back in through the soffit vents and into the attic again.

Given that the air flow through an attic is mostly based on convection and probably pretty slow, this may not be an issue in reality, but it would certainly make me think twice about doing it.

Eric Petroelje
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