About 20 days ago we had two of our joists doubled sistered because they had cracked in them. These joists are in the basement ceiling. I inspected the joists 10 days ago and they looked fine. I looked at them today and one of the joists has two cracks in it. I am concerned. I have included three pictures. One of them is from the bottom.

Here is a link to an old post of mine before they were sisterd: My Old Post

What should I do?

A Crack

A Crack

The view from the bottom

  • 2
    It's unfortunate that your contractor didn't select lumber more carefully. I don't consider a board with a crack running crosswise through 40% of the joist to be suitable in that role.
    – isherwood
    Commented Dec 21, 2022 at 17:36
  • "what should i do?" Since the basement looks unfinished, I would put a pole under the problem area to prevent further escalation and add stability to the floor above.
    – dandavis
    Commented Dec 21, 2022 at 20:00
  • @isherwood The crack occurred after the board was installed. I am concerned that it will get worse over time.
    – Bob
    Commented Dec 21, 2022 at 21:49
  • I miswrote that. I meant "... a knot running crosswise..."
    – isherwood
    Commented Dec 21, 2022 at 21:50
  • 1
    Assuming typical loading, the bottom of the joist is in tension. The middle image appears to show a crack at a knot extending from the bottom edge across a significant part of the height of the joist. That reduces the strength of the joist considerably. Had the board been flipped before installation the knot would have been in compression and the joist would handle a much greater load. Note that a crack or hole in the middle (height-wise) of the joist has little impact on the strength as long as the top and bottom edges are intact for 1/3 of the height.
    – HABO
    Commented Dec 22, 2022 at 4:01

2 Answers 2


Looking back at the original post, I thought I left an answer for the problem too, but could not find it.

Seeing how close the cracked part is so close to the wall, and the crack itself in my opinion is not much different than a hole drilled for a large plumbing pipe, which by code allows 1/3 of the width of the joist to be taken up by the drilled hole. It is a bit close to the top but there is a lot of good wood below the crack. With all this in mind a repair is barely needed. If the crack was in the middle of the span would be an entirely different matter.

But since you have the joists sistered already.....

In the first picture, the crack you show is a shrinkage crack that does not travel to the edge of the added piece, no harm there in my opinion. The second picture where the crack follows a knot all the way to the edge would be of concern if it was the only piece in the run. Since there are 3 pieces total, the original not having any cracks going out to an edge, and in addition, I doubt if any of the "new" cracks coincide with the original one in the old joist. With all that added wood/strength, IMO, you are in great shape.

If you did want to be more confident with what you have, I would suggest more fasteners in the sistered joists than what you have. The first picture you have, shows maybe only 1 nail visible in the area of the picture, there should be at least 6 or possibly 8. That is, 3 or 4 nails in vertical rows approximately every 16" or so apart. Since there is a crack now, some nails (or screws) could be concentrated around both sides of the cracks to keep them in check.

I still think you are in good shape, but adding the extra fasteners should be done anyway, when sistering joists.

  • The two new cracks are near where the old crack is.
    – Bob
    Commented Dec 21, 2022 at 17:21
  • 1
    I added a bit more to the answer.
    – Jack
    Commented Dec 22, 2022 at 3:36

Yep it depends on fastener placement. Add some around the crack. Back out a screw then dunk the threads in glue and reinsert. Bolts are always better in something like this, go all the way through the 3 joist. If the contractor is good he'll come replace the board and say thank you for calling. A knot like that is never acceptable for structural work, especially horizontal. I was taught to check studs the first time I went to a home Depot on my first job. Still check every board before use. The pallet from a supplier always has returns and they expect it. I would have glued all of that also, loctight x9 or loctight MAX in retail stores now. 10 bucks for a tube that would get all 4 surfaces,and the crack wouldn't matter. All the fasteners aren't showing but there should be screws top and bottom the whole length. I'd go in 1 to 1.5 from the top and bottom the whole length. 25 years experience, licensed contractor

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