Shrinkage cracks in joists

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KevP
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Location: Saint Paul, MN USA

Shrinkage cracks in joists

Post by KevP » Mon Sep 23, 2019 4:25 pm

Hey guys,
My house is from the 60s and i see some occasional horizontal cracks in some. They are mostly hairline cracks. None goes through it (no cracks from the other side)
One in particular is a bit longer. I can see that some joists are bowed slightly. I guess as the wood dried over the years it twisted a bit.
I remember my framing guy looked at it once and said that its ok. The city inspector also looked at when he was at my placs for another thing. Both said i can sister if i like but as long as its not sagging or causing bouncy floors it is mostly aesthetics.
Just wanted to see what you think as well.
Here is the joist:
20190923_171148.jpg
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20190923_171140.jpg
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20190923_171308.jpg
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I thought about sistering a 6 foot section to it but might not work as intended due to the bow since it is not flat.

Other joist have small cracks but mostly in the knots like this
20190923_171123.jpg
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Last edited by KevP on Mon Sep 23, 2019 5:08 pm, edited 3 times in total.

KevP
Posts: 72
Joined: Wed Jul 05, 2017 1:37 pm
Location: Saint Paul, MN USA

Re: Shrinkage cracks in joists

Post by KevP » Mon Sep 23, 2019 4:26 pm

The cracks in the nut also is only on 1 side

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A. Spruce
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Re: Shrinkage cracks in joists

Post by A. Spruce » Mon Sep 23, 2019 4:52 pm

Yup, absolutely common, absolutely nothing to worry about. Of the two, the knot is more worrisome, this one isn't particularly, but a large knot like that, especially when it cracks, significantly reduces the strength of the joist. Now, you can either sister it OR add blocking fore and aft of the knot and on both sides, thus tying this joist to its neighbors. Certainly a good precaution if you're going to cover the joists with drywall, but not a necessity based on what I'm seeing in the pix.
If the women don't find you handsome, they should at least find you handy.

KevP
Posts: 72
Joined: Wed Jul 05, 2017 1:37 pm
Location: Saint Paul, MN USA

Re: Shrinkage cracks in joists

Post by KevP » Mon Sep 23, 2019 5:08 pm

Thanks Spruce. I was reading that along the grain cracks are pretty common. However anything else across the grain is not good. He told me to worry if I see a vertical crack which would be across the grain. I read that cracks in knots are common however it is best to beef them up as you said.
My framer told me to grab short pieces of 2x10 (same as my joist) and double it up on side. He said 1 ft on each side of it would be more than enough. I have some 3 x 0.120 framing nails (not sure if that is 10d or not) which i used for my partition walls. Would that be enough or do you suggest something like GRK R4 screws?
I have few of these knots that im planning on doubling up on one side

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A. Spruce
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Re: Shrinkage cracks in joists

Post by A. Spruce » Mon Sep 23, 2019 6:09 pm

IMHO, a 2' or 3' board scabbed to the side of the knot isn't going to add any strength to the overall board. Think about the leverage that the length of board has on either side of that knot, a short scab will have zero affect on structural integrity. If you're going to go to the effort, I would use an 8' board at minimum, if not a full length sister.

Yes, you can use structural screws to attach the sister, not sure if GRK screws meet that spec or not, some construction adhesive wouldn't be a bad idea either.
If the women don't find you handsome, they should at least find you handy.

KevP
Posts: 72
Joined: Wed Jul 05, 2017 1:37 pm
Location: Saint Paul, MN USA

Re: Shrinkage cracks in joists

Post by KevP » Mon Sep 23, 2019 6:16 pm

Gotcha. The joists have cross members ties in few spots. I won't be able to easily sister anything more than 4 ft since dusting is in the way. As for blocking, do you mean full size blocking veritaclly added between the affectes joist and ita neighbour?

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A. Spruce
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Re: Shrinkage cracks in joists

Post by A. Spruce » Mon Sep 23, 2019 6:57 pm

KevP wrote:
Mon Sep 23, 2019 6:16 pm
As for blocking, do you mean full size blocking veritaclly added between the affectes joist and ita neighbour?
Yes. With accurately cut and tightly fitting blocking, that area will be far stronger. If you have any sponge in that floor at all, blocking everything on roughly 4' centers will stiffen it significantly. If you are adding any walls under these joists, then blocking won't be necessary, as the wall itself will support the joists and stop any deflection (sponginess) that may exist.
If the women don't find you handsome, they should at least find you handy.

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