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Community and Q&A

Ventilation for Encapsulated Crawlspace

Lindaloowho | Posted in General Questions on

Hi Everyone!
I was just confirming that, if I encapsulate my wood skirted crawlspace and do not have ducts in the crawl, is it okay for me to insulate the walls (not floor above), air seal with spray foam, vapour barrier, and dehumidify the space? Would some sort of controlled ventilation be necessary? I know the negatives of ventilated crawl spaces, but I was a bit confused by an article I read by Joe Lstiburek. Maybe I misread, or misunderstood, but I thought he mentioned active controlled ventilation in this scenario.

This is a cottage on piers, no insulation in walls or floors. I assume the floor assembly above crawl is not airtight and there will be some amount of air exchange. I don’t really want to add passive vents in the floor to communicate with crawlspace if I don’t have to.

Many Thanks,
Linda

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Replies

  1. Expert Member
    Peter Engle | | #1

    If you actively dehumidify the space, there is no need for additional ventilation. Your question is not completely clear about the crawl treatment. You mention a vapor barrier. If there is currently a dirt floor, the vapor barrier is very important, and the more airtight you make it the better.

  2. Lindaloowho | | #2

    Thank-you,
    Yes, there is a dirt floor. Should we bring the vapour barrier to the joists? Or should we leave some space for insect inspection. We live in Southern Ontario.

  3. JC72 | | #3

    IMO I would not use a skirt because, iirc, they are essentially impossible to air-seal. The best approach is to insulate and air seal the floor joists if you can get under there.

    https://www.buildingscience.com/documents/building-science-insights/bsi-115-crawlspaces-either-or-out

    1. Deleted | | #5

      Deleted

  4. Lindaloowho | | #4

    Thanks John,
    We are going to do our best. Taking up the skirt and insulation of the floor is too much for us to manage right now. The skirt was previously insulated, but not the sills and no vapour barrier was put down.
    We are going to rectify both of those and air seal like crazy.

  5. 1869farmhouse | | #6

    Homes on piers are generally treated differently than crawl spaces. I agree with the above, I’d forget about air sealing the skirt and insulate/air seal the underside of the floor joists. Closed cell foam is perfect for this application.

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