I just had a perimeter drain and sump pump installed in our crawlspace because it flooded frequently and severely during the rainy seasons. Before, I was under the impression that leaving the crawlspace vents open was the way to go in this climate (very wet winter/spring, very dry summers). Now, with the drainage system in place, I'm leaning toward closing off the vents, since (if the drain/pump system works) there will be no more standing water, and thus much lower humidity levels, and it would slow down the inevitable fouling of the new plastic sheeting from dust and such.

So, to seal or not to seal?

Thank you


1 Answer 1


Oregon resident here. You should keep the vents open if closed off things like radon have no place to go. Trapped moisture will cause rot, You may keep the water out but it will still be damp and it needs air flow.

  • 1
    You're not saying that radon will cause rot... Commented Jul 2, 2017 at 21:26
  • No radon can cause health issues. With vents sealed it really forces it into the living space.reworded so answer is clear.
    – Ed Beal
    Commented Jul 3, 2017 at 17:55
  • Yeah, radon can definitely be a factor in causing lung cancer and the only way to reduce radon levels if you have a radon issue is through vents. Trapped moisture that can't escape will definitely contribute to rot. I believe this depends a fair degree on the local climate. In the southeast, for example, venting might let as much moisture in as out. Commented Jul 3, 2017 at 17:59
  • Even if you don't reduce humidity much, pollutants like radon and other gases should be vented, and you may reduce mold spores, etc.
    – isherwood
    Commented Jul 3, 2017 at 18:00
  • This is a bit anecdotal at this point coming from me, but I've read pieces by engineers/builders in the deep south saying that venting attics in that area, for instance, can do more harm than good. In fact, I'll just go Google it... <computing>. Yeah, this is along the lines of what I remember ;-) buildingscience.com/documents/insights/… Commented Jul 17, 2017 at 20:57

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