Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?

 
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Old 05-12-2010, 08:53 AM   #1
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Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


I've not used LVL i-joists before, and wonder if this might be the time to use them. I know SYP* is cheaper, but wonder if (with this span) the advantages of straight & smooth outweigh the cost of the LVL i joists?

Project is a single story 18 x 20 or 20 x 20 addition, with only limited use of the attic space. Walls/joists are going to be 16 oc.

Anyone think I'm wasting time / money looking at the LVL on a project of this size?

Any hidden costs (over traditional dimensional lumber) I need to know about with LVL?

TIA

* FWIW IRC R802.4(2) allows SYP 2x10's to be used for unsupported spans in rooms of this dimension.
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Old 05-12-2010, 12:22 PM   #2
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


Size wise, wood I joists has serious advantages over solid syp You can span it without any additional supports. At 18 feet, 2 by 10 will have a lot of bounce and deflection compared to wood I joists. Also you can run the duct work through the joists which you cannot do with solid lumber. Speak to a reputable supplier of the material and they will let you know the guidelines for conduit/duct runs.

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Old 05-12-2010, 12:25 PM   #3
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


LVL ceiling joists? You have money to burn I guess. If this is clear spanned I dont know if I would feel comfy with 2x12 much less 2x10. if you cant break the span----- maybe TGI
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Old 05-12-2010, 12:52 PM   #4
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


Some I joists are made with lvl on the top and bottom flange, thats what he meant.
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Old 05-12-2010, 12:57 PM   #5
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


18' for 2X10 SYP, with two stiff backs
(hog backs for some of you),
is something I've done many times.
I always tell them that attics are for
insulation, not storage.
I see a couple of those ceilings fairly
regularly, and no problems 20+ years out....
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Old 05-12-2010, 02:16 PM   #6
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


Hmm. Another thought:

With up to a 20' span, would you recommend I go with factory made trusses instead of stick-framing?

They want a big, open room with no intermediate posts, beams, etc. I've always stick framed smaller rooms / sheds - but never attempted a span this big.

@ neolitic - you say two stiff backs; I presume you mean placing them @ 1/3 & 2/3 of the span - rather than in the middle?
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Old 05-12-2010, 03:04 PM   #7
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


We call them strong backs but three rows would definitley be helpful from distorting but sag is still going to happen. I never dealt with trusses either but considering the open room size this may be a perfect time to get a quote for some.

Give it a shot.
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Old 05-12-2010, 03:08 PM   #8
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


Quote:
Originally Posted by Panzer5 View Post
...............
@ neolitic - you say two stiff backs; I presume you mean placing them @ 1/3 & 2/3 of the span - rather than in the middle?
Yes.


Quote:
Originally Posted by tom m View Post
We call them strong backs but three rows would definitley be helpful from distorting but sag is still going to happen. I never dealt with trusses either but considering the open room size this may be a perfect time to get a quote for some.

Give it a shot.
That big a flat ceiling I think I'd notice
any sag, and I don't.
I did put braces @ 4' oc from the stiff backs
to the rafters too.
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Old 05-12-2010, 03:11 PM   #9
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


I think trusses are your cheapest and best bet.
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Old 05-13-2010, 08:19 PM   #10
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


Thanks.

I called my local supplier & was surprised at how reasonable the price was. Looks like I'll get my first experience with trusses (if they accept the bid...)

Once again, I appreciate the responses!
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Old 05-13-2010, 09:07 PM   #11
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


Good luck
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Old 05-28-2010, 09:58 AM   #12
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Re: Ceiling Joists For 18 - 20 Foot Room: SYP Or LVL?


Here are a few points on this topic.

1. I-joists typically are stronger than solid sawn but slightly less stiff (depending on the species of lumber). Meaning they have the strength for long spans but can be just as bouncy or more so than similar sized solid sawn. You need to calc them to be sure. I've written articles on this - please visit my site for more.

2. If the attic area might be used for storage it should be designed for the same live load as a floor, 40 psf. If not, it can be designed for much lighter live load, generally 10 psf, which will result in much smaller joists.

3. For long floor spans, I like open-web joists. But the attic truss idea is a good one too.

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