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Old 12-23-2010, 08:22 AM   #1
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Split floor joist


Hi all, I searched for some help on this topic before posting and have an idea of how to fix it, but I didn't see anything that addressed this specific problem.

I recently moved into my first house. I was replacing some insulation in my basement and I noticed a horizontal split in one of my floor joists. The joists run north-south. The split joist is the first one in from the east wall. The split is about 1/3 of the way down from the top of the joist, starts at the south end of the joist and runs north for about 3 feet. The top part of the joist has actually shifted 1/4" to 1/2" to the east. The split doesn't look recent. The house is 38 years old and I'm guessing that it settled over some time because the sill along the east wall has tilted or lifted up a bit as if the house settled to the east. It looks like previous owners have filled the 1/4" gap between the sill and the foundation with concrete.

Anyway, is what I just described a major concern? My first reaction was to sister the split joist (as I read in other posts), but I didn't know if bringing that joist back in line would cause any damage to either the floor above or the sill that the bottom is still attached to.

Thanks for any help you can provide.

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Old 12-23-2010, 09:32 AM   #2
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Split floor joist


I can't provide any help but I am facing a similar issue. In fact, I was just prepared to make a similar post. So I'm eager to hear the responses on this. My house was built in 56 and uses 2x8 floor joists. Steel beam down center with about a 13 foot span. Joists are 14 ft long and overlap on the beam. I have several joists with horizontal cracks as you. Some are hairline in nature, two of them the cracks are maybe 1/16" wide (probably not quite that wide). Guess I'm just concerned how structural significant this is and whether I need to start sistering all these joists like you mentioned? Like I said, eager to hear responses.

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Old 12-23-2010, 09:46 AM   #3
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Split floor joist


Solid wood horizontal structural elements loaded vertically, such as joists and beams, are prone to splitting for a variety of reasons. In many cases, the splits are not structurally significant. When wood dries, it shrinks, predominantly across the grain. Because the shrinkage is different in three directions (along the beam there is almost no shrinkage, and the shrinkage across the grain differs between the two axes), the beam develops large internal stresses independent of the loading.

The effect of the internal stresses is to cause cracking, usually parallel to the grain, often near the center of the beam where the horizontal shear is greatest. Because wood is expected to crack, proper design accounts for a certain amount of cracking, and compensates by specifying a larger beam than the loading requires (code factor of safety). If your beam was properly sized for the loading, hairline cracks, short credit card thickness cracks, and even relatively longer, deeper cracks are probably not structurally significant.

Wood will also permanently deflect under load over time, so the settlement in an old house may be completely unrelated to foundation settlement, and may be completely normal. One key question is whether the foundation has settled, which can only be determined by an instrument survey of the house.

The other key question is whether the framing is overloaded, which can be determined by checking design charts for the spans and sizes of the various structural elements.

If you have a large crack (greater than 1/4 inch wide, longer than 3 feet, or significanly displaced laterally), you may want to get an opinion from a structural engineer or architect. A hands on visit is essential, because an instrument survey to determine the amount of deflection is required.
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Old 12-23-2010, 10:07 AM   #4
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Split floor joist


This one sounds significant to me since you said its opening.
Previous post is correct hairline cracks along the grain=not big deal.
However any crack across the grain is a huge deal.

For your situation I had something similar recently.
I slowly jacked the joist into original position. By slowly I mean I went almost all the way, then over the course of days got it tight and then a litttle extra. Don't let the noises scare you, just go slow(course of days) for caution.
I then sistered in a 2 by of the same size, extending about 4 ft on both sides of the crack. I attached with liquid nails and carriage bolts, but that might have been overkill.
After that was attached I slowly removed the jacks.
I used 2 bottle jacks to push 2x4's by the way.
A floor jack works a lot better(done this before), but I don't own one.
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Old 12-23-2010, 12:08 PM   #5
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Split floor joist


The joist doesn't actually sag, it's shifted sideways along the split. I attached a picture of what the split looks like. The top shifted with the house, the bottom is still attached to the sill.
Attached Thumbnails
Split floor joist-img_0692.jpg  

Last edited by scottyv81; 12-23-2010 at 12:11 PM.
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Old 12-23-2010, 01:52 PM   #6
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Split floor joist


Daniel- great info, thx.

Do you know where the design charts can be located to determine if the frame is overloaded?

Hairline cracks don't appear to be much in the way of concern. What about card sized cracks almost the length of a joist? Or located in middle sections. All this would explain squeaky,bouncy floors I imagine. Is sistering & cross braving the answer in the bad spots?

Apologize to OP - not trying to hijack post but it all seems related and didn't think two posts would be desired about similar topic.
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Old 12-23-2010, 02:42 PM   #7
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Split floor joist


The Southern Pine Institute has design charts for allowable span on commonly used framing lumber, specifically a variety of southern and yellow pines. The Forest Products Laboratory in Wisconsin has design properties for a wide range of less commonly used lumber. Building codes typically incorporate design charts for common species of lumber. These are the best places to look. Just make sure you read very carefully the instructions for use of the charts, there are typically a variety of factors that must be incorporated to determine the allowable load on a given structural element.

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