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Discussion Starter · #1 · (Edited)
We're doing a 2nd story addition using 2x12 Doug fir @ 16" on center spanning about 16' to the bearing wall. This is well within the tables.

There is one part, about 5' wide, in the middle of the 2nd floor where the span bumps out to 19'-8". This is still within the tables but barely, 19'-10" is the max for 16" o.c..

We're thinking of tightening up the spacing in this area to 12" o.c. in the thought that it should make it stiffer and more like the rest of the framing but I'm not sure if this is a good idea or not. I think it should help.

Does anyone have any experience with this? TIA for any advice, pro or con.
 

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diplomat
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I think it's a good idea. Will it interfere with mechanicals or anything? You could also double the joists at that area, which will make both areas have roughly the same deflection. Better than 12" and closer in strength.
 

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Discussion Starter · #4 · (Edited)
I think it's a good idea. Will it interfere with mechanicals or anything? You could also double the joists at that area, which will make both areas have roughly the same deflection. Better than 12" and closer in strength.
I didn't think of doubling them, the 12" o.c. won't interfere with mechanicals I think but it is tighter than doubled 2x12's at 16" o.c. albeit only 2-1/2"
. So you think the deflection will be closer than if it's a single at 12" o.c. I'm not sure how to calculate that as it's the whole system that needs to be calculated, not just the single unit.

Also thanks Scipio for the heads up on the 30 psf for sleeping areas vs. the 40psf for living areas.
 

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Use any of the beam deflection calculators, if you're looking to match deflection. You don't have to consider the floor as a single system unless you're doing something like vibration analysis.
 

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Anything over 12' I just go with wood I beams. Lighter. Easier. And the same price as 2x12 if not a little cheaper depending on where u are at.
 

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And collapse faster in a fire.
 

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Throwing the fire part was a great point, but if my place burns I want it all gone to start over not live in a charred anything.
 
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