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Reducing Crawlspace Moisture: Close, Cover or Keep Vents Open?

  • Transcript

    LESLIE: Now we’ve got Floyd in Iowa on the line who needs some help with a crawlspace.

    FLOYD:  I just recently purchased a home. And in part of the basement, I have a crawlspace. And when the inspector came in to do the inspection on the house, he recommended that I put plastic down and to close the vent. When I was listening to you guys’ show the other day, I noticed that you guys said something about keeping the vents open so nothing ventilates into the house. So I was just kind of trying to find out, you know, which direction should I go? What kind of plastic should I use? And does it sound like a good idea?

    TOM: OK. So, let me clarify for you. First of all, reducing crawlspace moisture is importantPutting a plastic vapor barrier down across the floor of a crawlspace is always a good idea. You use the plastic Visqueen – the big, wide sheets – overlap them about 3 feet. Try to get as much of that surface covered. What you’re doing is preventing some of the evaporation of soil – of moisture up through the soil – so that’s a good thing.

    In terms of the vents, the vents should be opened throughout most of the year except, perhaps, just the coldest months of the winter. So if you close it, say, November and December and maybe January, that’d be OK. But for the rest of the year, those vents should be open because it helps take the moisture out.

    FLOYD: Now, I also have insulation up in the rafters of the floor joists. Is it a good idea to put – or to seal that with any kind of plastic at all or should I leave those exposed?

    TOM: Nope. No, you can leave it exposed just like that. It needs to ventilate.

    FLOYD: OK. Good deal.

    TOM: Alright? Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.

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