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Unread 11-25-2011, 12:21 AM   #1
Toddman
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2x4 Truss Joist Span

I don't see these 2x4 truss joists very often and not sure what the deflection is? Have a customer who wants 1/2" thick slate installed. The 2x4 trusses are 12" deep and 24" o.c. from what I can see from a small unfinished area in the basement. The unsupported span of the area to be tiled is 24'. Front of the house to the back. That whole area will be tiled. That seems like a very long span to me? Can't find any stamps or markings to get any info.
What do you think guys? Bob?
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Unread 11-25-2011, 06:50 AM   #2
RJCarney
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Todd

See this thread;

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Unread 11-25-2011, 06:59 AM   #3
K_Tile
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12" deep 24ft floor truss is over spanned in my opinion. Definitely not going to hold stone at L720.
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Unread 11-25-2011, 08:44 AM   #4
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RJ, the basement is finished so beefing up the joists is not an option, thanks.
Kevin, my gut feeling is that a 24' span is too far also. Surprisingly there doesn't seem to be any bounce in the floor, it feels pretty good. Which makes me wonder if there's some kind of header (or something) running at mid point that I can't see?
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Unread 11-25-2011, 09:00 AM   #5
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I agree with Kevin.

I don't think you could even meet code (L/360) with those joists at a full 24' span, Todd. But, then, I can't imagine a suitable support beam in mid-span if you've got a finished, flat ceiling below.

Gotta be missing something, though, if you can't make that floor bounce quite a lot from above.

My opinion; worth price charged.
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Unread 11-25-2011, 09:16 AM   #6
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Yep, got the flat ceiling below. I was surprised too as to how solid it felt. Half the floor now is 3/4" hardwood, and the other half is vinyl. My gut says to walk away from this one, but also curious as to why it seems stiffer than it should be.
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Unread 11-25-2011, 09:24 AM   #7
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Folks have relied on the ol' jump test for ceramic tile floors for years, of course, but I'm not thinking I'd wanna trust that for stone over a span like that. Can you cut a hole big enough to pole your head in and look? Hole in either the ceiling or existing subfloor?

Customer would be content with the transitions required for the additional subflooring and tiling substrate required even if you did accept the joist structure?
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Unread 11-25-2011, 10:07 AM   #8
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Can't cut a hole in the ceiling as it's finished. Possibly in the subfloor. Even though the ceiling is flat (no vissible support beam) do they ever run supports through the webs? Or is it even possible? Not sure how all that works. But trying to learn more about these. Not sure what I'd be looking for, but maybe I'd know if I saw it.

Yes, customer is fine with me adding another 1/2" layer of plywood and regular Ditra over existing 3/4" plywood. Only one room to transition into, and they've got some thick carpet and pad in there.
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Unread 11-25-2011, 10:20 AM   #9
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Not likely anything running through the webbing, Todd, not much real value in that. If you can't support the bottom chord, you don't gain much. It is possible to go through the webs, attaching to the vertical members, which are attached to the bottom chord, which...............

But in your situation I don't see that having been done. There could be some sort of support beam running across that area with the trusses supported on it, but without knowing the span of that kinda support it's difficult to guess.
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Unread 11-25-2011, 10:35 AM   #10
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I think I'm going to see if I can cut the "exploratory" hole.
Now, on the other side of the basement there's what I assume is a load bearing wall. The span in that area would be cut in half (12') I'm assuming I can tile (slate) over that span, no?
Actually not sure technically how to tell if it's a load bearing wall when everything is finished?
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Unread 11-25-2011, 12:41 PM   #11
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Generally determined by the construction of the wall and what it's supported by, Todd. If it's sitting on a structural concrete slab and has a doubled top plate or the studs directly under the joists above and is fully sheathed on at least one side, it's likely it was intended to be a support wall.
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Unread 11-25-2011, 12:55 PM   #12
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Thanks CX.
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Unread 11-25-2011, 01:38 PM   #13
chuck stevenson
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Todd,

Here is a link to a pdf on wood truss construction.

http://www.trusscomponents.com/pdf/F...ss%20Guide.pdf

I have seen this detail before and hopefully it is what you have

This would allow a flat ceiling. By any chance are the as built plans available?
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Unread 11-25-2011, 02:34 PM   #14
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Thanks Chuck. Yea I will have to check if the plans are available or do the exploratory hole. There must be something like that going on in there.
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Unread 11-25-2011, 02:40 PM   #15
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Even so, If there's a beam that cuts the span in half to say 12', how do we know what the deflection on that is. Is this going to support natural stone?
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