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Old 08-28-2011, 02:33 PM   #1
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Joist span question


I currently have 2x8 24 oc joist for my kitchen floor, a couple of them where cut completly through by the old owner. Im planing on changing the 2 joist and beefing them up, sistering a second 2x8. Im just wondering how much more strenght does this add? The span is 11'8" with 7" both sides sitting on sinder block and beam.

From what I can find online, 2x8 24oc is good for 11' spans (if the info i found is correct). Would the sistering be enough to bring this up to code?

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Old 08-28-2011, 03:01 PM   #2
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Joist span question


If the original joist was cut completly through as you stated then sistering a joist to the cut joist is not adding any extra support. Why not add a couple more joists and get the joists at 12" on center? That would help the strength of the floor being that you are over spanned already.

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Old 08-28-2011, 05:59 PM   #3
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Joist span question


I first remove the cut joist of course then replace with a double.

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If the original joist was cut completly through as you stated then sistering a joist to the cut joist is not adding any extra support. Why not add a couple more joists and get the joists at 12" on center? That would help the strength of the floor being that you are over spanned already.
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Old 08-28-2011, 06:10 PM   #4
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Joist span question


I like what simonb said. add new joist and they will be 12'' onc. Also, replace the cut joist like you posted.

If you plan to put tile down your 24" oc will not cut it. In fact 12" oc will only work with ceramic, not natural stone. If you sister them on 12" oc it will work for stone.

I ran your spans thru the calculator on the John Bridges site.
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Old 08-28-2011, 06:19 PM   #5
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Joist span question


I wasnt going to add 12oc, i was going to keep it 24oc and just sister the joists. Can you let direct me to the calculator you used?

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I like what simonb said. add new joist and they will be 12'' onc. Also, replace the cut joist like you posted.

If you plan to put tile down your 24" oc will not cut it. In fact 12" oc will only work with ceramic, not natural stone. If you sister them on 12" oc it will work for stone.

I ran your spans thru the calculator on the John Bridges site.
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Old 08-28-2011, 06:50 PM   #6
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Joist span question


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I first remove the cut joist of course then replace with a double.
There's no need to do that.
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Old 08-28-2011, 08:12 PM   #7
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Joist span question


No need to do what? Replace the cut one? Double up?

I rather replace it when there is a foot missing from the joist.

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There's no need to do that.
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Old 08-28-2011, 08:15 PM   #8
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Joist span question


Can someone confirm what the span of a 2x8 on 24c is? and maybe point me to a calculator?
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Old 08-28-2011, 08:25 PM   #9
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Joist span question


http://www.awc.org/calculators/span/...rcalcstyle.asp
10'3" for Spf #2

There's also:
http://www.johnbridge.com/vbulletin/deflecto.pl
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Old 08-28-2011, 08:29 PM   #10
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No need to do what? Replace the cut one? Double up?

I rather replace it when there is a foot missing from the joist.
1' of the joist is missing? Still, no need to replace it when you can just nail the double right next to it. Your giving yourself more work for no reason. What harm will the joist cause by staying there?
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Old 08-28-2011, 08:32 PM   #11
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Joist span question


Removing it might make it easier to get the new joists in though. It's only about 15 minutes of work with a sawzall.
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Old 08-28-2011, 08:34 PM   #12
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Joist span question


Thats exactly it. There is no rim plate and they poored cement between the joists. Taking it out takes me 15 minutes but saves me from having to break all kinds of cement.

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Removing it might make it easier to get the new joists in though. It's only about 15 minutes of work with a sawzall.
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Old 08-29-2011, 05:11 AM   #13
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Thats exactly it. There is no rim plate and they poored cement between the joists. Taking it out takes me 15 minutes but saves me from having to break all kinds of cement.
You have to break cement to put in the second joist anyway.What about when you take out the existing joist, you have to cut every nail from the subfloor into the top of the joists. You will want to secure the subfloor back to the new joists.

Gluing the top of the new joists isn't enough. If you do take out the existing joists, you can get the new one in first and place a 2x4 flat against the top of the new joists (with glue)with the 3-1/2" facing the bottom of the subfloor and the 1-1/2" part against the top of the new joists. Screw through the 3-1/2" part of the 2x4 into the bottom of the subfloor,then ail through the new joist into the 1-1/2" part of the 2x4.
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Old 08-29-2011, 07:08 AM   #14
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Joist span question


They sistered the joist with a 4 foot 2x6 when they built the house. Im not sure why they added the 2x6 because its only about 4 feet long and serves no purpose, its not even glued and nailed/screwed. But either way, removing both of these leaves me with only having to break a small peice of cement. Trust me, this way is easyer hands down.

The room above is my next project, so i will be screwing the flooring into the new joist when the time comes.

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You have to break cement to put in the second joist anyway.What about when you take out the existing joist, you have to cut every nail from the subfloor into the top of the joists. You will want to secure the subfloor back to the new joists.

Gluing the top of the new joists isn't enough. If you do take out the existing joists, you can get the new one in first and place a 2x4 flat against the top of the new joists (with glue)with the 3-1/2" facing the bottom of the subfloor and the 1-1/2" part against the top of the new joists. Screw through the 3-1/2" part of the 2x4 into the bottom of the subfloor,then ail through the new joist into the 1-1/2" part of the 2x4.
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Old 08-29-2011, 09:10 AM   #15
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Joist span question


I guess if you are good with an overspan then do it the way you want. If you want to do it right then add joists to 12"oc a little more work but then you know it's right.

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