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What’s wrong with this picture (double stud wall)?

maine_tyler | Posted in General Questions on

I came across this:
(which hopefully there’s no rule against posting source)
apparently by BSC.

Nearer the bottom they show pictures of ‘right’ and ‘wrong.’ There is only one wrong picture… here:

I am simply stumped as to what they are trying to point out, for there is no caption explaining. Based on the ‘right’ pictures, they are not necessarily finished products, so lack of air/vapor barrier doesn’t seem to be the focus. Also other ‘right’ pictures show OSB, so that doesn’t seem to be it either. What am I not seeing?

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  1. maine_tyler | | #1

    I apologize,
    A better source link is this:

    it appears to be U.S. Department of Energy, and this link provides images with captions. The 'wrong' image states, "Wrong – No air barrier installed between the walls and a larger gap between the walls that needs sealing."

    So the uninteresting mystery is solved... i guess... It is strange though as the first two 'right' images also have no air barrier (yet at least). Additionally I have no idea what they mean by "larger gap between the walls that needs sealing."

  2. GBA Editor
    Martin Holladay | | #2

    I agree that this is very confusing. This comes from the Building America Solution Center -- a web site with lots of errors and problems. (Here is a link to an article that discusses the multiple problems associated with this web site: A Web-Based Information Resource From the DOE.)

    If GBA readers want to know where to find the photos on the web page, they can be found by clicking the tab labeled "Training."

    The photo you are talking about appeared without a caption when I clicked it. Eventually I figured out a way to make the caption appear. Below is the photo with the caption.


  3. GBA Editor
    Martin Holladay | | #3

    So, it appears that this Building America web site insists that all double-stud walls need an air barrier between the two stud walls. I disagree. I think it's perfectly OK to establish the air barrier either (a) at the exterior sheathing, or (b) at the interior drywall, or (c) at both the exterior sheathing and drywall.

    The caption uses non-standard English. Does the caption writer think that the builder of this wall should have had a larger gap between the two rows of studs or a smaller gap? Who knows? The sentence is ambiguous.

    Clearly, a larger gap would allow for a higher R-value. Is that what the caption writer wants to see? Hard to know.

    What about a smaller gap? That would provide a lower R-value. Is that what the caption writer wants to see? Perhaps -- but if so, why?

    Finally, in what way does the gap "need sealing"? Does it need sealing between the subfloor and the bottom plates? Does it need sealing at the top plate area (not shown in the photo)? Hard to say.

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