Remodeling our home and found out a few of the floor joists have dry-rot where the floor joist sits on the wall top plate. The wall to wall span that the joist sits on is 11'. Three questions on best approaches.

Note: I will be having county inspections in California for this and other new work.

I'm thinking of adding a sister joist next to the one that has the dry rot to raise up and support the joist in question, but lumber is sold as 2x12 or 2x10... But the existing joist is 1.5"x11" exact. So in theory the lumber would need to be 2x11.5".

  1. Do I just get a 2x12 and cut down the full length to size? Or do they sell lumber at these (weird) dimensions?
  2. If freshly cut wood is installed, in theory would the 1.5x11" shrink? Or is this something that shouldnt be considered?
  3. Can I add a partial sister joint where the dry-rot issue (one end of the top plate) is at or do I need to span the full 11' for both ends to sit on a top plate?

Thank you in advance!

  • 2
    2x12 nominal has actual dimensions of about 1.5x11.25, so 2x12 may match what you have well. Unless your home is very old, I would expect it to be so.
    – blarg
    Commented Jul 18, 2022 at 17:38
  • 2
    If the bottom of the 2x12 can hang down(not have a flat ceiling on it) then just need to notch at each end, instead of the whole length. Might also use a 2x10 plus a 2x2 on top to make 11 inches(not sure).
    – crip659
    Commented Jul 18, 2022 at 17:39
  • Is the house quite old, more than 50 years? That should explain the the joists being actual size.
    – crip659
    Commented Jul 18, 2022 at 18:23
  • have a 6 pack ready
    – Traveler
    Commented Jul 18, 2022 at 18:49
  • @crip659, yep its literally at 50 years old as of this year
    – Paul M
    Commented Jul 18, 2022 at 20:13

1 Answer 1


1.5" x 11" close enough to 2x12. Dimensional joists have crowns so 1/4" might not make any difference. Depends on what you are doing with the finished floor and the current flatness. SPF #2 is kiln dried so shouldn't shrink unless you are installing it wet.

If you want to "repair" your joist you'll need an engineer to sign off. I have had engineers sign off on a girdle to "fix" a large notch that my electrician put into the middle of a 2x10 that was already over span. For the cost of the engineer to do that though you might as well just sister or replace the existing unless you have significant wires / pipes that can't easily be re-run.

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