I cut open my ceiling drywall to take a peek in my "attic" (about 20" of vertical space) before I go about having a skylight installed. I have a flat roof and I noticed one of the rafter/joists is cracked. The span of the board is approximately 13', the crack is what you see: less than 2'

Is the fix to simply sister (screw) a 3' length of 2x8 to the problem area? I don't really have access to the other side of the board unless I cut another access hole in the ceiling which I'd like to avoid.


1 Answer 1


Yes, but a few feet longer than the defect on either side. If you were to look at all of your joist, this is probably only one of many that would have a similar defect.

  • Of the joists that I could see, I did not find any more with a split defect. This particular joist is directly aligned with the front door handle so perhaps that is to blame
    – dabi
    Jan 22, 2019 at 6:26
  • 1
    The knot in the wood was at the edge of the board. They have a tendency to split in half. The knot splitting weakened the board in that area causing the split down the center because of the weight of the roof. It's possible the door had something to do with it, but it's probably just the knot. Jan 23, 2019 at 7:11

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