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  1. #1
    Join Date
    Oct 2012
    Location
    Houston, TX
    Posts
    249

    Default sistering a new joist

    Crawling under the house (pier and beam) I found a joist I do not like one little bit. A few of my joists have some minor termite damage that I plan to repair with bondo, but this one has some heavy damage on the bottom 4 inches for about three or four feet, bad enough that I could probably just rip the bad parts out by hand. The termites are gone(though I plan to spray anyway)and I want to fix this issue myself before I have the house leveled as I know this minor work will cost me less to do myself.
    Anyway, how do I compensate for the fact that my original joists are "true" sizes, as in rough-edged and actually 2x10 as opposed to 1&7/8 x 9&5/8? Do I buy a size wider (2x12) and notch at the support in the middle?



    The span will run the width of a 14' room with a 4x4 beam near the middle and 4x6 beams on the ends. I do know to use adhesive and a healthy number of decking screws.

  2. #2
    Join Date
    Sep 2009
    Location
    florida
    Posts
    598

    Default Re: sistering a new joist

    Get the next size joist up. If it's a 2x10 use a 2x12 and rip it down to the size needed. Glue together with liquid nails and screw together
    Gizmo

    Cut it 3 times & it's still to short.
    Inventor of the Miter Master Plus.

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  3. #3
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,621

    Default Re: sistering a new joist

    Personally I would notch the ends rather than cut a larger size down.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  4. #4
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
    1,522

    Default Re: sistering a new joist

    if 2x10 is only smaller by 1/4 or so you can easily use those it saves you having to cut them down.. but you will need to make wedges to shim the new joist up flush with the tops of the existing joists on the ende.. then toenail as needed along the length of it to keep it flush. from there nail it off to have it fully laminated.

    using bondo doesnt do anything for hte strength of the woood. it just fills voids
    fire up the saw and make some dust

  5. #5
    Join Date
    Sep 2009
    Location
    florida
    Posts
    598

    Default Re: sistering a new joist

    Quote Originally Posted by JLMCDANIEL View Post
    Personally I would notch the ends rather than cut a larger size down.

    Jack
    Yeah that will work as long as there are no plumbing,elec pipes ect strapped to the bottom of the joist or in the joist space
    Gizmo

    Cut it 3 times & it's still to short.
    Inventor of the Miter Master Plus.

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  6. #6
    Join Date
    Jan 2010
    Location
    Northern Virginia
    Posts
    1,001

    Default Re: sistering a new joist

    Screws for sistering are not to code, unless signed off by an engineer. You have to use 16d nails.
    If you have to use screws, use Timberlocks or Headlocks,or Spax.
    Deck screws are a waste of time, as they lack anything close to adequate shear strength.
    So is the adhesive, IMO.
    It comes down to the fasteners, nailing(bolting) pattern and the bearing. An LVL is about 15% stronger than structural fir in the same depth.
    It's not going to be any fun getting a new straight joist into a situation with a center carrying beam in an old, saggy floor. For that reason I would not go any deeper in size than the original, and that probably means ripping down the new member.
    Casey
    Remove not the ancient landmark, which your fathers have set.

  7. #7
    Join Date
    Oct 2012
    Location
    Houston, TX
    Posts
    249

    Default Re: sistering a new joist

    Thanks for the input gents. Fortunately there is no sag in this particular spot in my floor, just preemptive action on my part.

  8. #8
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,418

    Default Re: sistering a new joist

    I'm going against the grain here, as I often do. since your joist is still straight, I do not see any reason to go to a 2x12, a 2x10 will work just fine. It needs to span the full width of the room, all 14' of it so if this rests on top of he center beams and rim beams, then it will probably be a 16' length.

    Now to make up for the gap, make wedges out of HARDWOOD. Soft woods will compress too much when they are just a thin section like in a wedge. Been there, done that. BTW, a modern 2x10 will support a 14' span on 16" centers.

    Since it is running the full span, it does not actually have to be mechanically attached to the original beam, but I would anyway. I would use an adhesive and a few through bolts with "body" (large) washers. I would use at least 6 1/4-20x 4.5" to clamp the boards together, then nail or screw.

    Now as for spraying. You need to be very careful when you are working with potentially dangerous chemicals in a confined space. My recommendation would be a sodium borate solution like Timbor. I would usually also recommend Boracare, which has been used on several TOH projects, but Boracare is premixed with ethylene glycol (antifreeze) which is highly toxic if ingested. About 1 oz is lethal.

    I would recommend Timbor mixed with water per directions on the package. You can google for the product. It is pretty safe to use and relatively environmentally friendly and one of the most effective products you can use. It is not only a broad spectrum insecticide that has been used for centuries, it also is a mildewcide that prevents rot and fireproofs the wood as well.

  9. #9
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
    1,522

    Default Re: sistering a new joist

    if your using gun nails youll notice that gun spikes have teh same diameter as screws.. my engineer doesnt really care which we use as long as we draw the new joist tight to the old with hand spikes first. one top and bottom every 2'
    fire up the saw and make some dust

  10. #10
    Join Date
    Oct 2012
    Location
    Houston, TX
    Posts
    249

    Default Re: sistering a new joist

    Lots of good info, thank you. I plan to go the DIY route using a borate and boric acid mix for the spraying, holding off on the glycol.
    The next trick will be getting a 16' piece of lumber to my house owning only a full size sedan. Time to make friends with my local building supply.

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