Last night, I observed that one of the floor joists that is supporting the house is badly cracked. I can shine a flash light through the crack. I am thinking this is a major safety issue. My fear is that the floor is going to collapse.

How should I go about fixing this?

Note: When walking on the floor above, I hear squeaking.

Picture The other side. enter image description here

  • A picture would help. Most times a crack can be common and not structural weakling. A vertical crack is not good, but easy to fix by adding/nailing same size wood to the joist.
    – crip659
    Commented Oct 20, 2022 at 11:19
  • 1
    That appears to be a floor joist terminology-wise. To quote Douglas Adams, Don't Panic! It's repairable, most usually by applying new lumber to one or both sides of the damaged member. The load is shared by many joists, and spread by the flooring, so if all of its neighbors don't have similar cracks, there's very little risk of collapse, as already answered.
    – Ecnerwal
    Commented Oct 20, 2022 at 11:42
  • 1
    It's not good, but it's not a sign of eminent failure. It will need to be repaired, but it can wait a bit. Do you hear creaking or cracking sounds when you walk on the floor above this?
    – FreeMan
    Commented Oct 20, 2022 at 12:01
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    I do hear creaking sounds when I walk on the floor above.
    – Bob
    Commented Oct 20, 2022 at 12:29
  • That appears to be near the end of the joist. The joist needs to be strongest in the middle, and the ends are often trimmed down on the bottom corner so that things fit together better. You should keep an eye on it, but there's no need to replace it.
    – Hot Licks
    Commented Oct 20, 2022 at 12:51

3 Answers 3


It doesn't look too crazy, and the good news is it looks really dry. If this is the only split floor joist, your house is not going to collapse. The first thing to do is familiarize yourself with the names of the material that support a floor. (The attached picture might help you understand what the difference is between a floor joist, rim board, sill plate. But a quick google search for the definition of these names may be more helpful) enter image description here

Steps I took to repair my split floor joist. These are the steps my neighbor directed me to do. He is a highly qualified licensed builder in Michigan.

  • Measure the split floor joist from the rim board to 3feet PAST the split floor joist where the wood is not split.
  • "Sister" 2 new pieces of wood on both sides of the split floor joist. Like a Sandwich. The split floor joist is the meat, the 2 new boards are the bread.
  • The ends of these 2 new boards should touch the "rim board" and rest on the "sill plate"
  • The other end of these new boards should extend at least 3 feet past the damaged floor joist.
  • Use nails instead of screws to secure the two new boards to the damaged floor joist.
  • Hammer them in a zig zag pattern (A nail at the top of the new boards, A nail at the bottom of the new boards) spaced apart every six inches to secure them in place.

Before jacking up any floor joists, its also important to think of what is above this? How much lift is needed? Is there plumbing above it? A tile floor? All things to consider just in general while jacking. I personally wouldn't jack UP a damaged floor joist before repairing it first. Especially considering that it already has 1 vertical load that its already not properly supporting.

  • 4
    In general I'd agree with you, some questions, though: "Sandwich them between the split joist." Don't you mean "sandwich the split joist between them"? "Use structural nails instead of screws" Do you mean "framing nails" (16d 3" nails) or "structural screws instead of nails"? Not sure what the picture adds, since it's showing new construction and doesn't seem in the least related to the repair at hand. Remember, your audience is often people who are doing things like this for the first time and need explicit and clear directions.
    – FreeMan
    Commented Oct 20, 2022 at 14:20
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    First. I have NO experience in this. That being said, it seems intuitive to me that you would jack up the old joist before installing the sister joists. That way, when the repair is complete and the jack removed, the sister joists will be carrying some of the load and will relieve a partial load from the original (compromised) joist. Without jacking first, it seems that the sisters would only carry a load if the original joist cracked further. Am I wrong on this?
    – RetiredATC
    Commented Oct 20, 2022 at 14:35
  • RetiredATC A valid point. I would be concerned with damage to the original floor joist with jacking. What are your thoughts on temporary sistering the split floor joists w/ only a couple nails, jacking the joist up, and then sliding the sister boards deeper into the Rim joist one at a time? Commented Oct 20, 2022 at 14:48
  • @JetteBeckett I'm not sure i completely understand the steps you outlined but if it gets some of the load onto the sister joists when the repair is done I'm all for it!
    – RetiredATC
    Commented Oct 20, 2022 at 15:09
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    Note: Structural screws. Not drywall screws or decking screws. Structural screws are meant for framing purposes. They're expensive, but they're designed for the task at hand.
    – FreeMan
    Commented Oct 20, 2022 at 17:48

That's a floor joist not a rafter and it serves to support the floor and anything on that floor above. It does not support any upper story or the roof as these have their loads transferred to the outside walls or any interior load-bearing walls.

Homes are built with significant redundancy so that a single failing member is not going to cause a collapse. But, under certain circumstances, high wind loads, high snow loading, high floor loading, etc. that could be a problem.

You should take steps to correct this issue as soon as possible but it's unlikely that this is an emergency situation unless there are other floor joists nearby that are also cracked or damaged.

As a temporary measure, if you are concerned, you could support it from below with a jack post:

Jack Post


You need to treat the crack like a hole. So you can use a bracket that brings that joist up to code. https://joistrepair.com/collections/featured-products

$60 and takes 20 minutes to install. You also need to add bridging to both sides.

enter image description here

The bridging will deflect the twisting of that joist when there is a load that could cause the crack to expand. Based on it being so close to the wall and having a bracket binding the area a few bridges on each side (minimum 3) should set you up long term.

So you need to buy a bracket, 2 2x4s, and have access to a saw and nail gun would help. ~2 hours of basic work.

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