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Old 01-12-2012, 05:46 PM   #1
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max joist span


Hi all.
Plans call for 2x10 spruce lumber at 12"oc. Total length is 17 ft supported on a ledger board on one side, and on a triple beam at the other end.

They are installed but it seems to me that they are a bit small for this run length...

Thoughts?

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Old 01-12-2012, 06:02 PM   #2
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Quote:
Originally Posted by gkaro View Post
Hi all.
Plans call for 2x10 spruce lumber at 12"oc.
Thoughts?
what is the load?


Last edited by TarheelTerp; 01-12-2012 at 06:07 PM.
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Old 01-12-2012, 06:08 PM   #3
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17' seems overspanned. If you put a beam at midspan you can go up to 16" o/c.
Check with your local building department for local codes.

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Old 01-12-2012, 06:31 PM   #4
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Quote:
Originally Posted by gkaro View Post
Hi all.
Plans call for 2x10 spruce lumber at 12"oc. Total length is 17 ft supported on a ledger board on one side, and on a triple beam at the other end.

They are installed but it seems to me that they are a bit small for this run length...

Thoughts?
http://www.awc.org/pdf/STJR_2012.pdf

Its all a matter of how much deflection and bounce you are willing to tolerate

Mark
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Old 01-12-2012, 07:11 PM   #5
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It's actually right from the city. Does it make a difference if it for a roof or a livable floor? I assumed they are the same due to snow load.
Thanks
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Old 01-12-2012, 07:16 PM   #6
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Quote:
Originally Posted by gkaro
It's actually right from the city. Does it make a difference if it for a roof or a livable floor? I assumed they are the same due to snow load.
Thanks
They'll probably be very different.

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Old 01-12-2012, 07:20 PM   #7
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Oh...best guess....which would need stronger lumber?
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Old 01-12-2012, 07:31 PM   #8
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Quote:
Originally Posted by gkaro
Oh...best guess....which would need stronger lumber?
Uh...which is heavier, the roof
full of snow and wind or a floor full of furniture and stuff (live load)?

That's a stupid answer. That's what the planning and building department are for.

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Old 01-12-2012, 07:36 PM   #9
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Floors usually require a higher loading than roofs, but not always. I knew an area that had the following loading requirements: Roof: 10DL 30LL House Floor: 10DL 40LL Deck: 10DL 50LL.
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Old 01-12-2012, 07:53 PM   #10
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A learned discussion on allowable span, and you haven't told us where you live, what code you are under, or if there are any unusual loads on your span. For all we know, your joists are holding up air. Course you do indicate that the lumber was sized on the plans, so are you wondering if the designer made an error?

If joists are sized according to code, they will be sized for the more restrictive of two conditions. Condition one is the strength of the joist. Condition two is the allowable deflection. These conditions are set out in the code, and the allowable deflection criteria is very different for a floor than for a roof. And the loads for a floor are normally very different than the loads for a roof.
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Old 01-12-2012, 08:28 PM   #11
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From IRC 2009.

I have no idea if this actually pertains to your situation but it may.

Andy.
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Old 01-12-2012, 09:31 PM   #12
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I was going to say that one used to be able to span 16' with a 2x10, fir, 12' with a 2x8. Now the spans have been shortened because of the quality of the wood.

So I was going to say you would be quite comfortable with 17' and 12" spacing.

But there you have the chart right in front of you and it says 17-9. That is for spruce, which has to be the worst.

If you want to stiffen it up some more, then I would suggest putting in 2 or even 3 sets of solid wood blocking. Then you will really have something.
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Old 01-12-2012, 11:41 PM   #13
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I am in Canada. The joists that I am referring to are for a flat roof on a one floor addition. I instructed the designer to size everything so that a second floor could be added on top in the future....possibly. Then the roof would become a floor.

The permit was not done for a second floor so the entire plans look like overkill for just the first floor. I'm just questioning now if the designer actually called the 2x10s correctly for the second floor???

Last edited by gkaro; 01-12-2012 at 11:48 PM.
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Old 01-12-2012, 11:48 PM   #14
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The addition of a second floor does not affect the size of the first floor joists. 2x10 fir at 12" o/c sound ok for 17' span. Probably calls for some blocking or cross bridging too would be my guess.

You may want to look into TGI's (I joists) could probably go 16" o/c
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Old 01-12-2012, 11:49 PM   #15
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Mae ling. Thanks for your reply. I corrected my post. Please reread.


Last edited by gkaro; 01-12-2012 at 11:52 PM.
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