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Unread 07-27-2014, 02:25 PM   #61
dhagin
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Quote:
Originally Posted by PC
Followup to the derating for field conditions post, if we apply the 15-25% reductions to the 14' 2x8 T beam (16" spacing) , the result is a range of L/405 to L/356 versus L/200 for a standard 14' 2x8.
Well done. Not there's an injuneer what knows something about differences and real world expectations with site-built stuff compared to on-paper theoretical stuff.

I think we're edging ever closer to what one can expect from these site-built assemblies.
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Unread 07-27-2014, 02:37 PM   #62
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Hey Dana,

Yeah, lots variability on site versus factory. Zeafals's point about loading is worth a follow up. I use a screw jack under the 2x4 after I've initially placed it to unload the joist and ensure the new board is firmly seated in the adjesive before screwing in place. Did I mention it's good to have a helper?

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Unread 07-27-2014, 02:45 PM   #63
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very useful thread

great option instead of sistering . . . So, for the fat kid in the back row . . .

2 by 4 glued and screwed to a 2 by 8 will get us to proper deflection for tile
but not for stone??

Even if we don't get full glue coverage we can assume we get to at least
L/400 in a real-world scenario.

. . . and is that over 14 feet?? WOW!!

Unsightly threshold transitions goodbye . . . I'm tired of explaining to GC why
we need an extra layer of ply to make it happen.

thanks all

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Unread 07-27-2014, 02:49 PM   #64
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Hey Steve,

The plywood you mention will help with deflection between the joists. I don't think it'll do a lot for joist deflection which is the topic here. But yeah, I'm sorry I never thought of it.
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Unread 07-27-2014, 02:54 PM   #65
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Yes, based on the assumptions as stated. Just need to be sure to get a good bond, 0.1 to 0.4 mm adhesive thickness is optimal. Having done this in my home I can tell you it takes time to get all the joists properly built up, glued and screwed (and wear a hat, the Pl is tough to get out of your hair)

What John said re between joist deflection.

You got internet out there in Hill country John?

Last edited by PC7060; 07-27-2014 at 03:00 PM.
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Unread 07-27-2014, 06:24 PM   #66
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So, PC, if you had the option to do either one, would you get more bang for your buck by sistering with the same size joist (or at least the next size down), or attaching a 2x4 to the bottom of the joist?

It seems that if you don't get optimal adhesion on the bottom chord, you lose a lot. But it's much harder to screw up the sistering techniques.
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Unread 07-27-2014, 09:02 PM   #67
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Kevin, I prefer adding another joist if possible because it's faster and you don't lose any headroom. The configuration of the hall bath I just did (12 months ago really?) made it too complicated to add new joists so I created L beams out of the 2x8 to get the required stiffness.

For the master bath I pulled the entire floor and added several new double joists that were nice and straight without a bunch of nasty knots. Big improvement over what I removed.
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Unread 07-29-2014, 06:39 AM   #68
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Quote:
Originally Posted by PC
You got internet out there in Hill country John?
I have an ATT hot spot which is the only Internet available in these parts. I put out large dollars to sit in on what y'all are talking about.

. . . and I am truly happy to learn what a simple 2X4 will do. I'm in the preliminary stage of building a house (by myself).
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Unread 07-29-2014, 07:22 AM   #69
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John: Note that adding a 2x4 to the bottom is a technique to increase the stiffness of existing joists. For new construction you can just increase the joist size. Using a 2x10 rather than a 2x8 provides a similar increase in stiffness as adding a 2x4 to a 2x8. You need to run the numbers to determine the actual deflection rating for each method. But using a 2x10 is simpler and avoids any potential issues with installation methods, adhesive creep, or inspector approvals.
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Unread 07-29-2014, 09:08 AM   #70
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Larry, it's easier still to specify engineered wood joists so you can select just what you need for the application and be assured of meeting that requirement with material that is straight (except for designed-in and consistent crown) and consistent from piece to piece. Can make life a lot easier at not much additional cost at all.
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Unread 07-29-2014, 09:20 AM   #71
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I still like to use these when possible:

Name:  floor trusses.jpg
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They're probably more expensive than I-joists, but you can run plumbing, electrical, and HVAC through them without having to hack them to pieces.

Engineered joists, if they've not been cut improperly, will also not have the splits and cracks that are sometimes associated with 2x joists.
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Unread 07-29-2014, 09:41 AM   #72
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Quote:
Originally Posted by CX
it's easier still to specify engineered wood joists so you can select just what you need
Definitely agreed. Just wanted to point out that adding a 2x4 to a joist probably never makes sense for new construction. For new construction there are better ways to get the desired stiffness.
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Unread 07-30-2014, 07:31 AM   #73
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Quote:
Originally Posted by John Bridge
I have an ATT hot spot which is the only Internet available in these parts. I put out large dollars to sit in on what y'all are talking about.
We have several of those units at our office too, only takes one or two uses a month for them to pay off.

Quote:
Originally Posted by John Bridge
. . . and I am truly happy to learn what a simple 2X4 will do. I'm in the preliminary stage of building a house (by myself).
Agree, we do structural metal as part of our business so its second nature that a "T" beam in steel or aluminum is much stronger than just the plate alone. Course it did take me a bit to realize that the same principles apply to wood, just a matter of find the right constants to plug in for the material type.

I agree with the rest of the team that it's generally much easier to just size the joists and beams properly to begin with. Unfortunately some of us are still dealing with "2x8 construction that are in the low 300's on the deflecto" as Kohito pointed out way back in in the original 2008 incarnation of this thread.
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Unread 07-30-2014, 05:08 PM   #74
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Didn't mean to infer that I would use the system on my new house. I do think it's great that we have the 2x4 option for remodelers.
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Unread 07-30-2014, 05:18 PM   #75
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Understand John, Just figured I'd put that it out there for anyone who was following along.

New home, pretty cool, I see ingineer'd joists and glu-lams in your future. Too bad I'm so far away or I'd sign up for the barn raising that Paul is putting together.
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