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Old 06-21-2008, 03:37 PM   #1
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Will 22 foot 2x12's span 20 feet over a basement and not sag over time? one load bearing wall close to the end of the joist. Don't really want to pay the cost of the I joist

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Old 06-21-2008, 11:49 PM   #2
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I don't have a span chart/code book in front of me, but I can safely tell you HECK NO. 20' is a pretty tough/nearly impossible span to get out of dimensional lumber with normal floor loading unless a beam is incorporated. Adding a bearing wall to the joists totally kills the prospect.

Sagging over time isn't the issue. Floor deflection under load is. If you were to try to span that far, you're essentially creating a trampoline. There will be perceivable bounce in the floor. It'll fail inspection if your work is permitted.

You need to consider a beam to break that span up.

As for I-joists, an LPI 32 series 11-7/8" joist will only span 20'-2" at 40/10 psf loading....Without any bearing walls. You need 14" joists or a beam, and the support of a design professional.

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Old 06-22-2008, 06:11 PM   #3
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http://www.raisedfloorliving.com/spantables-2.shtml

This is what I was going by.
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Old 06-22-2008, 07:10 PM   #4
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18'-10" is the span for 16" oc #2 2x12's, but that is with nomal floor loading. When you add a bearing wall to the joists' workload, you'll far exceed the capabilities of what is already an overspanned joist.

Even without the wall sitting on the joists, you need to understand that those are maximum spans. I assure you, you'll be very disappointed in the floor's performance at that span.

This is not one of those places to "value engineer" something.
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Old 06-22-2008, 07:13 PM   #5
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Also, bear in mind that those are span tables for southern pine lumber. In order to meet your span, you'd need 12"oc #1 material (and no bearing wall sitting on them).

Have your supplier price #1 southern yellow pine in 20' lengths. They're likely not a stock item either.

I-joists will be cheaper, I can pretty much guarantee it.
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