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Sistering a joist

Tonys1228 | Posted in Construction Techniques on August 2, 2017 03:21am

I need to sister an existing 17ft long 2×10 floor joist.

Reason is , after sistering the one joist I need to attach a 6ft long beam at 90 degrees… And will be hanging (3) 2x10s off it.

 

Problem is…..the original joist are spaced only 12″ apart and each end of the 17 joist has 6″sitting on the sill plate.  How can I get a joist to fit in that small of a space?  

Will shortening the additional sister joist b y 6″… (leaving 3″ on each sill plate) reduce the strength too much?

I’m not even sure I can squeeze it in by shortening it 6″

Btw….I’m creating an opening in the floor joist for a spiral stair case.

Tony

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  1. junkhound | Aug 02, 2017 10:20pm | #1

    no need for bearing if nailed properly -

    lookup lateral shear

    1. Tonys1228 | Aug 06, 2017 03:58pm | #2

      Thank you for your response.... So you are saying the added joist ends don't need to rest on the will plate as long as its fastened correctly to the existing joist?  I am spanning 17' 8".

      After doubling i will be connecting a header about 6' from one end .  header will be about 6' long and have 3 joist hanging off it.

      1. calvin | Aug 08, 2017 07:39am | #4

        Tony

        You should be able to add joists that do sit on the wall a couple inches on each end.  Bevel the top of the joists you are adding so they will tip up easily. Stuff one end in and over to one side, pull back to center after you get the other end up.

        why go wrong when you can go right?

        1. Tonys1228 | Aug 17, 2017 05:20pm | #7

          Got her done

          Thanks to everyone for your help. 

          I was able to get 2.5 inches of bearing on both ends.

          All I did was clipped about one half inch of the top corner of one end.

          Not bad since I was alone and had no help lifting..

    2. Tonys1228 | Aug 06, 2017 04:26pm | #3

      Spann Distance from sill plate to sill plate edges is 16'8"

      Joist length is 17'8"

      1. calvin | Aug 08, 2017 08:16am | #6

        Tony

        heres another reason to make the joist long enough to sit on both walls.  You can do this solo.

  2. DanH | Aug 08, 2017 08:05am | #5

    The main thing to understand is that, if the original joist is sound and evenly loaded, the most stress in on the middle third.  If you anchor the sister to the outer third on each end (and, of course, also tie it to the middle) then the original joist is greatly strenghtened.

    If you can manage to have the sister rest on the supports on each end so much the better, but that's not necessary in most cases.

    Do use something substantial to do the joining.  Through-bolts are the best choice.  But don't put the fasteners too near the ends, to avoid splitting.

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