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2×10 floor joists vary in width

Tapcon | Posted in General Questions on

I’ve got foundation decking laid and I now see some gaps between the rim joist and the underside of the decking. Turns out some of the 2x10s are at least 9 3/8″, and a few maybe almost 9 7/16 ” 
How common is this? Some gaps look to be almost 1/4″ between the rim joist and the underside of the decking, which now happens to be screwed and glued!!

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  1. Expert Member
    BILL WICHERS | | #1

    Lumber is not a precision product. Are you concerned about the 1/16” variation? That’s pretty close for lumber. If you have gaps on the tops of the joists, between the joists and the decking, then it’s probably from things not being aligned correctly during construction. You generally align all the edges that will be on the finished side, and there are a few other things you’re supposed to check too (like the orientation of the grain). I’m not sure how you’d correct this without taking things apart and redoing it.


    1. Tapcon | | #3

      Yes, I think 1/16th is pretty close for dimensional lumber. But I've got gaps of up to 3/16 or 1/4".

      Of course you're right that the finish side should be flush. I hired a framer that was recommended by an HVAC guy. I left him on his own and he made a great number of mistakes. Like attempting to put the floor joist blocking in AFTER he screwed and glued the deck down.

      My inclination is to tear off the entire deck and start over with some capable framers. That is a very expensive do over. But now all of the floor joists are covered with mold and the underside of the decking is condensating for mold growth as well. And good framers are all too busy.

  2. walta100 | | #2

    At this point it sounds like ruff framing and generally rule is + or – ¼ inch is good enough.

    I am thinking the gap you can see now under the exterior wall will close up once the weight of the wall and roof are in place.

    I do wish I had gotten out the caulking gun and filled the gaps in the band joists before the sub floor went on.


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