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Old 07-25-2009, 01:14 PM   #1
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Full length sister joists when existing joists overlap?


I'm trying to add three sister joists to a single existing joist, but I'm not sure how to handle the side where the overlapping joist extends about two feet from the girder? Do I hack the overlapping joist back to the center of the girder to allow the sister joist to rest on the girder?

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Old 07-25-2009, 02:37 PM   #2
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Full length sister joists when existing joists overlap?


You need to cut back for at least 1-1/2" bearing, if not more. Lap the outside one past the bearing. Why do you need 3 joists, what could be so heavy?

You may find they nailed the ceiling to the overhanging wood. A joist should not lap in distance past the bearing more than it is thick. Joists lap minimum 3" with 3- 10d nails. And solid blocking at all bearing points to prevent rotation. Be safe, G

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Old 07-25-2009, 03:38 PM   #3
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Full length sister joists when existing joists overlap?


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Originally Posted by GBAR in WA View Post
You need to cut back for at least 1-1/2" bearing, if not more. Lap the outside one past the bearing. Why do you need 3 joists, what could be so heavy?

You may find they nailed the ceiling to the overhanging wood. A joist should not lap in distance past the bearing more than it is thick. Joists lap minimum 3" with 3- 10d nails. And solid blocking at all bearing points to prevent rotation. Be safe, G
Thanks for the input! I'm reinforcing so I can achieve l/720 for 12" marble. I also have two severely notched joists in the middle third of the span under my bathroom (I can thank the 1950s plumber and HVAC guys for that little gem). If that wasn't bad enough, one of the notched joists was cut (it's attached to a header) to make room for the shower plumbing.

The girder is three 2x10s, so I guess I'll have to cut the existing overlapping joist back so that I'll have room for 2-1/4" bearing.

Oh yeah, the joists are 2x8, spanning about 12'. I'm actually thinking of adding three or four 2x8s to each existing joist.

Last edited by benjamincall; 07-25-2009 at 03:47 PM. Reason: Changed "trimmer" to "header"
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Old 07-25-2009, 05:30 PM   #4
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Full length sister joists when existing joists overlap?


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Originally Posted by benjamincall View Post
Thanks for the input! I'm reinforcing so I can achieve l/720 for 12" marble. I also have two severely notched joists in the middle third of the span under my bathroom (I can thank the 1950s plumber and HVAC guys for that little gem). If that wasn't bad enough, one of the notched joists was cut (it's attached to a header) to make room for the shower plumbing.

The girder is three 2x10s, so I guess I'll have to cut the existing overlapping joist back so that I'll have room for 2-1/4" bearing.

Oh yeah, the joists are 2x8, spanning about 12'. I'm actually thinking of adding three or four 2x8s to each existing joist.
Why do you have to cut the overlapped joist? Why not just sister the three joists up against the existing one going the opposite direction of the overlapped joist? Is there something in the way?
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Old 07-25-2009, 05:46 PM   #5
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Full length sister joists when existing joists overlap?


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Why do you have to cut the overlapped joist? Why not just sister the three joists up against the existing one going the opposite direction of the overlapped joist? Is there something in the way?
Good question. I'm replacing plank style subfloor with plywood. The two bathroom walls will be unsupported once I replace the planks. In one instance, I'll have to sister on the side that overlaps to provide support for the length of the wall.
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Old 07-25-2009, 06:08 PM   #6
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Full length sister joists when existing joists overlap?


??????????? What part of Hopatcong?

Last edited by skymaster; 07-25-2009 at 09:11 PM. Reason: Spellin fairy off duty
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Old 07-25-2009, 06:35 PM   #7
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Full length sister joists when existing joists overlap?


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Good question. I'm replacing plank style subfloor with plywood. The two bathroom walls will be unsupported once I replace the planks. In one instance, I'll have to sister on the side that overlaps to provide support for the length of the wall.
Why can't you leave the planking underneath the walls and just but the new decking to the planking?
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Old 07-27-2009, 07:28 AM   #8
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Full length sister joists when existing joists overlap?


I guess I could rip the plywood back about 18 inches, so the planks that I haven't yet cut are still resting on the two outer joists in the bathroom. I believe the plywood is slightly thicker than the planks. I was just hoping to replace them with a nice uniform piece of wood.
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Old 07-27-2009, 10:52 AM   #9
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Full length sister joists when existing joists overlap?


Ben: if anything the plywood should be thinner that the t&g flooring. I agree with Joe Leave what is there, use temps or what ever means needed to hold up what is there and frame, sister whatever needs to be done, run the ply up to existing t&g. At the joint between t&g and ply run a pc of 2x or 3/4 ply a bunch under the T&g glue and screw it and then run ply oever it and glue and screw that together, this way the joint will not flex or at least only a a very minimum amount

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