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  1. #1
    Join Date
    Feb 2008
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    Tennessee
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    Default Mixed-Sized Joists

    Been doing this for twelve years and saw something for the first time. While inspecting the roof structure from the attic I noticed the use of two different sized joists with no rhyme nor reason of a followed pattern and was just wondering if this is allowed? Several 2x6's used, intermingled with 2x8's with no recurring or noticealbe pattern, no specific locations (such as valleys) just randomed placed about.

    Any thoughts?

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  2. #2
    Join Date
    Aug 2011
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    Bennett (Denver metro), Colorado
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    Default Re: Mixed-Sized Joists

    If the 2X6s meet the requirements for span and load, then I don't see why it is wrong, even if weird and extra work to keep the top line of the rafters even. That doesn't look like professional work which might be a red flag, even if the rafters don't violate any structural requirements.

    If you choose not to decide, you still have made a choice.

  3. #3
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    Default Re: Mixed-Sized Joists

    Lon, thanks for the reply. Yes, I looked it up and found that span limitations, etc. and wrote it up accordingly. Sloppy job to say the least through! Thanks again.


  4. #4
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    Aug 2012
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    Rock Hill S.C.
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    Default Re: Mixed-Sized Joists

    It's not perfect, but nothing is, I have seen a lot worse.
    Most likely the framers ran out of 2x6's and finished up with the 2x8's. Typically you install rafters intermediately as needed to get the ridge in place, then fill in the remaining spaces which would explain the random placement.


  5. #5
    Join Date
    Mar 2007
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    Columbus GA
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    Default Re: Mixed-Sized Joists

    The ridge board should be =>1" larger than the rafter, even if the rafter is larger that required.

    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

  6. #6
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    Aug 2012
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    Rock Hill S.C.
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    Default Re: Mixed-Sized Joists

    Quote Originally Posted by Rick Cantrell View Post
    The ridge board should be =>1" larger than the rafter, even if the rafter is larger that required.
    What's so bad is, in the 1rst pic, you can see they nailed a 2x strip on the bottom of the ridge board to get it flush.


  7. #7
    Join Date
    Feb 2009
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    Southern Vancouver Island
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    4,549

    Default Re: Mixed-Sized Joists

    In custom built homes, I have seen similar for a reason - if the span for the rafters on one side of the roof is longer, they upsize the rafters.

    In those pics, I see all 2X8 on one side, so I wouldn't call it random. But that's just what I see from these pics.

    For odd-sized rafters meeting at the ridge, it would be better to lap them, IMO.

    I thought I saw a cleat attached to the ridge board as well, but it could be a split that he wanted to repair with screws. Some of the cuts are a little off, but I don't see a significant structural defect.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  8. #8
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    Apr 2008
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    Western Massachusetts
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    536

    Default Re: Mixed-Sized Joists

    Since when is a 2x8 only 6-3/4" deep?

    Quote Originally Posted by Chris McIntyre View Post
    What's so bad is, in the 1rst pic, you can see they nailed a 2x strip on the bottom of the ridge board to get it flush.
    But in the 3rd photo there's no evidence of that, which makes me curious about why those fasteners are there in the first photo.


  9. #9
    Join Date
    Jul 2010
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    Summerville, South Carolina
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    Default Re: Mixed-Sized Joists

    Sometimes framers just try to use the wood that's available to them.....sometimes there are other reasons.....making economical use of the wood that's there, insulation requirements, plan specifications or maybe that was the only wood on the job that was long enough. As long as it meets span and load requirements and is properly braced to prevent deflection it is no problem.


  10. #10
    Join Date
    Nov 2010
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    California
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    Default Re: Mixed-Sized Joists

    It appears as though 2x8s or larger were ripped to the odd size of 6 7/8. Not a good idea.


  11. #11
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    Hercules, CA
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    Default Re: Mixed-Sized Joists

    How about the other end of the 2x8's? Did they over-notch the 2x8's at the top plate to even out the roof level with the 2x6's? The code allows a notch of 1/4 of the depth of the member at the top plate (IRC R802.7)

    Thom Huggett, PE, SE, CBO

  12. #12
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    Jul 2010
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    Summerville, South Carolina
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    Default Re: Mixed-Sized Joists

    Quote Originally Posted by Thom Huggett View Post
    How about the other end of the 2x8's? Did they over-notch the 2x8's at the top plate to even out the roof level with the 2x6's? The code allows a notch of 1/4 of the depth of the member at the top plate (IRC R802.7)
    If 2x6's are sufficient for the load and are notched why would using a 2x8 not be ok for the same load provided there was adequate bearing at the plate .....even if the notch was slightly bigger?......there is an exception to 802.7 that permits the notching of the cantilevered portion of rafters down to 4".


  13. #13
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    Aug 2011
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    Hercules, CA
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    Default Re: Mixed-Sized Joists

    Quote Originally Posted by Ray Thornburg View Post
    If 2x6's are sufficient for the load and are notched why would using a 2x8 not be ok for the same load provided there was adequate bearing at the plate .....even if the notch was slightly bigger?......there is an exception to 802.7 that permits the notching of the cantilevered portion of rafters down to 4".
    Over notching can cause splitting of the member, and not necessarily parallel to the length of the member, so you could end up with a smaller section than at the support. Each joist will split differently. If the joists are over-notched they can be evaluated by a structural engineer, or in some cases you can add skewed, top-flanged joist hangers to each joist to support the notched portion of the joist.

    The exception in 802.7 is for the eave side of the rafter, not the main span.

    Thom Huggett, PE, SE, CBO

  14. #14
    Join Date
    Mar 2012
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    berkeley
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    2

    Default Re: Mixed-Sized Joists

    Quote Originally Posted by David Bertrams View Post
    It appears as though 2x8s or larger were ripped to the odd size of 6 7/8. Not a good idea.
    Yes, this is a VERY important point. One aspect of the grading of non-engineered lumber is knot location -- such as how far the knots are from the edges. Ripping it down you might now have a knot right on the edge, so a 2x8s ripped to 6 7/8 is NOT as good as a 2x6, even though a non-expert would think it would be better.


  15. #15
    Join Date
    May 2010
    Location
    St. George, UT
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    217

    Default Re: Mixed-Sized Joists

    Most of the structural concerns have been hashed out. One situation where you may see something like this would be that 2x6 was all that was needed for structural but the 2x8s where used because of insulation requirements in rafters at the bottom end of the 2x8s. (hope you follow what I wrote


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