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Daylighting in crawlspace and insulation for wood-framed portion?

Jason Huffine | Posted in General Questions on

So as our build is progressing, we decided that the landscape really necessitated a poured wall.  The slope is from front to back and doesn’t seem that high until you shoot it with a string set to level.  The front foundation wall at less than 3′ at the front entrance and at the back a little over 9′.  So to save some money on the foundation, the foundation contractor recommended daylighting, which means the foundation walls are staggered.  Ultimately, the back wall will be at just over 9′, but will be a combination of concrete wall at around 4′ and the additional 5′ will be framed in wood.  I will be encapsulating the crawl space myself and am looking at some EPS foam boards to insulate the walls, especially if I can before the framers start soon.  My question is with regards to the “daylighted” wood-framed portion of the wall.  Typically, blocks of foam board are placed on the band joist between the floor joists.  Would you recommend doing the same on the “daylighted” wall portion?  Or would I do just as well and save a little money using ROXUL Rock Wool insulation on that part?

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    Jason,

    GBA has several articles on this topic. See https://www.greenbuildingadvisor.com/article/building-an-unvented-crawl-space and also check out the side bar.

    I build a house on a lot with a similar-sounding topo. Ultimately, I decided to do a full basement. It wasn't that much more expensive than a tall crawlspace.

    1. Jason Huffine | | #2

      I have read that actually, and a bunch of other material. Unfortunately, there's not an easy way to make ours a basement. We're on solid rock! Had to form the footings and anchor them with pins to the rock below. With the front-to-back slope, that pretty well takes basement out of the picture. As for the insulation, all the articles I've read seem more focused on the foundation wall whether concrete or cinder block mostly due to the potential for condensation. But I'm assuming the dynamics should be much different with the wood framing portion right? Or am I overlooking something? That's why I figured rock wool might be a good option there and cheaper per foot than the foam board.

  2. GBA Editor
    Brian Pontolilo | | #3

    Hi Jason,

    I believe that the wood framed portion of the crawlspace should be detailed like any other above-grade wall. Of course, you'll want to make sure that your thermal and air barriers are continuous from the crawlspace floor, to the concrete walls, to the framed walls, even as you change materials. Those are the details you'll need to work out.

    If you have a drawing of this crawlspace foundation, it may be helpful for us to see how it is being built. You may get more specific detail recommendations from other members

    1. Jason Huffine | | #4

      My current understanding (sorry I don't have any details, just what the GC has explained) is 2x6 sill plate on the shortened concrete foundation wall, frame to top of wall (garage foundation is poured to the highest level, so the framing will go up to match). Then top plate with band joist on top just like any other. There's just a transition to consider. Since I'm required to leave a 3" inspection window, I'll be stopping the vapor barrier just short of the concrete wall. If I use foam in the wood framed portion, I thought I'd seal with foam like you would the blocking in there. The wood framed portion just wouldn't have a vapor barrier.

      1. GBA Editor
        Brian Pontolilo | | #5

        Hi Jason.

        What will be on the outside of the wood framed portion of the wall?

        1. Jason Huffine | | #6

          Sheathing will be zip. There will not be any exterior insulation as it's not necessary in our zone. And where exterior trim/siding is concerned, that's actually still up for discussion. Our GC mentioned the possibility of stucco which can be applied to both parts, making it look seamless. At least that'll be the goal. All non-foundation walls will be hardi siding. I've added some pictures if it helps.

          At the moment, I've decided to go with foam boards even into the wood framed portion, leaving a 3 inch termite gap of course. I was surprised (but probably shouldn't have been), but this was actually less expensive than floor insulation and will ensure everything is visible underneath. However, if the gurus on this site see a potential issue, I'm all ears and don't pick the material up until Friday! ;)

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