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Encapsulating Crawlspace of Pier Foundation

gcav0 | Posted in General Questions on

I live in New Orleans and most articles and videos I see about crawlspaces, well basically every article and video, has a partially enclosed crawlspace with vents. Easy peasy to close up and encapsulate.

I have nothing like that and my house is on concrete block columns where it’s completely open. Should I just build a bunch of walls around all the gaps and encapsulate it like normal in the humid south?

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    gcavo,

    There is nothing wrong with houses on piers, they just need the attention to be paid to the floor, not the walls as you would with a crawlspace. Air-seal and insulate as best you can.

    The big advantages of pier foundations are that in humid climates like yours they are much less prone to moisture problems than crawlspaces, and much less likely to experience damage in floods.

  2. jamesboris | | #2

    Malcolm is right. The answer is NO.

    You will find endless videos from high performance building channels talking about how a hermetically-encapsulated crawl is the only way to go. In a hot-humid climate, a tiny leak in this encapsulation can be disastrous. Many high performance framing techniques offer a great blower door test on Day 1, but include details that experienced builders (ignorant though they may be of blower door tests) would rightfully scoff at. Caveat emptor.

    I'm doing a new build, my first one that's going for utmost air-sealing, etc. details -- and I'm doing it on a totally open crawlspace. Here are some articles about insulating the floor. Air-sealing is like... just look at it really well and you'll probably see where air can get in.

    https://www.lsuagcenter.com/NR/rdonlyres/D33F711D-DC4B-4E4C-9ED6-A97DCE9DB026/79805/pub3187insulatingraisedfloorsLOWRES.pdf

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

    https://www.greenbuildingadvisor.com/article/crawl-spaces-vs-skirts

    https://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces

    tl;dr: Don't believe the hype that you need to encapsulate or perish. This is a forgiving, durable, inexpensive assembly that just isn't the strongest from a thermal perspective -- but in New Orleans, you don't need that. Most of the year, floor insulation will do almost nothing. But, do air seal it.

    1. Expert Member
      MALCOLM TAYLOR | | #3

      Boris,

      Have you seen this house? It has some really practical details for a low house on piers: https://www.southmountain.com/wp-content/uploads/2019/02/19-Small-Home-Harmony-Article-PDF.pdf

      1. jamesboris | | #4

        I hadn't, thanks for sharing. Some cool details. But I will say... to me, an 18" crawlspace is a nightmare. Many details I see online are good for years 1-10, but questionable beyond that... but 18"? That's terrible the minute you install it haha. I'd only advise the approach for an easy-access crawlspace (joists 3'+ above the ground) that grading has ensured won't fill in with runoff over the years. In the south, I'd also advocate using a landscape cloth and maybe gravel to prevent vegetation.

        That said, their floor insulation approach is creative. I don't know if it was cheaper or easier, in the end, than it would've been to cut-and-cobble 4" rigid foam strips between their 2x12s. I've got some models of the thermal bridging of the bottom such joists and it's pretty minor, but granted, I don't live in a cold climate.

    2. gcav0 | | #5

      I haven't read the New Light article and that was very helpful, thanks! So at a minimum air seal underneath the floor, but I could also insulate like in that article such as with closed foam or the foam boards under the wood?

      I did see one example of this in one of the many books I'm reading about building science and insulation, but it didn't really dive into it and was basically an example pic of one of many ways of thermally isolating the house.

      EDIT: This thread gave me new ideas for search terms to use in Google and I found a research paper done by LSU in New Orleans and Baton Rouge that talks exactly about this! :

      https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.lsuagcenter.com/nr/rdonlyres/d33f711d-dc4b-4e4c-9ed6-a97dce9db026/79805/pub3187insulatingraisedfloorslowres.pdf&ved=2ahUKEwip_NXYhPL4AhWAmWoFHZw4ArkQFnoECAUQAQ&usg=AOvVaw3nFw_sHN_K8-gUU5-IqDr9

      1. Expert Member
        MALCOLM TAYLOR | | #6

        gcavo,

        That's the same link James posted. It looks packed with good advice for your situation.

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