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Unread 08-24-2008, 05:50 AM   #1
scuttlebuttrp
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New deflection requirements article

This article is a bit technical dealing with new requirements concerning deflection/ live and dead loads/ fancy stuff like that. Maybe one of the smart engineer peoples around here can figure it out and explain it to us common folk. I do like the part that says the tile guy can't be held responsible for the framing no more though. Does this change the deflecto at all?

http://www.iccsafe.org/news/bsj/1207_Wood%20Bits.pdf
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Unread 08-24-2008, 07:39 AM   #2
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That article was published late last year, Royce, and the provision you like best is included in the 2007 version of the TCNA Handbook.

Essentially the article is just pointing out that the dead load for floors designed for a ceramic tile installation are likely to exceed the common residential spec of ten pounds per square foot distributed load, and that some methods, especially those using mud, can exceed it pretty substantially. Nothing new there at all.

For any buildings built to recent residential code, especially those using engineered wood floor systems, you can be pretty confident in presuming a tile installation using contemporary methods will fall within the acceptable deflection range. More traditional mud methods, as they point out in the article, can pose additional considerations. And older residential structures, which we deal with a lot here, can be a different consideration, too.

Our Deflectometer is based upon a ten-pound dead load, but the pertenant spec (modulus of elasticity) used for the lumber types is pretty conservative. Injineer Bob (bbcamp) made it so when he and Dave (davem) designed that little calculator. And it uses the whole load (ten dead and forty live) in the calculation, making it a bit more conservative.

Are there tile installation methods that may exceed the Deflecto calculations? Yeah, I think there probably are. We'd need Bob to tell us exactly what the Deflecto thinks, though. But overall, I think it's quite adequate to our purpose here. I can always find a span table that will allow longer unsupported joist spans for a particular wood specie than will the Deflecto, even if I use a twenty pound dead load.

I think we're still safe with our generalized calculation tool.

My opinion; worth price charged.
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Unread 08-24-2008, 08:01 AM   #3
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CX, i'm sure glad you said all that, saved us a lot brain cells. Hammy
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Unread 08-24-2008, 08:10 AM   #4
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Oh, c'mon, youins guys, that article ain't that complicated.

Y'all actin' like a buncha carpet layers.







Boy, I hope it's a long time before I have me another carpet question.
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Unread 08-24-2008, 09:41 AM   #5
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CX said it pretty well. The design load is 50 pounds per square foot and the modulus of elasticity is on the low end of the expected values for the species given. It's a good tool for evaluating a floor system by a homeowner. Professional engineers who will be stamping the drawings will probably not use the tool, but evaluate the floor system in accordance with the actual material specifications and applicable building codes, and probably will be able to qualify a floor that would not be acceptable to the Deflectolator. That's where the PE earns his money.
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Unread 08-24-2008, 09:28 PM   #6
scuttlebuttrp
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So if I'm doing a normal CBU or Ditra floor there's no problem. But if I'm doing a mudfloor I need a higher deflection rating? What about bracing in between joists for deflection there? Or do you just run a double layer of ply? Is there an easy way to figure these calculations that normal people can do?
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Unread 08-24-2008, 09:43 PM   #7
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Well, no, Royce, not exactly.

You still need the same deflection "rating" if you will, but you may need to meet that deflection criterion calculated at a higher dead load than you otherwise might have used in your calculation. You're still looking to meet the same deflection standard of L/360 (or L/720).

While it's possible to calculate the design deflection on site, you're far better off just carrying a joist span table along with you and referring to that. Injineer Bob and his ilk can whup out their little handbook with alla E numbers for different kinds of wood and other factors and throw a calculation on the structure for ya, but I just use the tables.

You're generally gonna be guessing at the lumber specie and grade in older structures anyway, so you ain't gonna get it 'zackly right most of the time.

If the folks who engineered the structure knew there was to be tile set per F141 or F145 and didn't build for it, you can still wave your TCNA Handbook at'em and say it ain't your fault. Don't know who's gonna be on your side at that point, but it's your best shot.

Unless you framed the floor.

Between-joist blocking and extra subflooring, while a good idea, won't help your joist deflection problem if you have one. And both will actually add to your dead load.

My opinion; worth price charged.
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Unread 08-24-2008, 09:59 PM   #8
scuttlebuttrp
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When I asked about the blocking or extra ply I meant as far as the between joist deflection goes due to the dead load of the deck mud. Not the joist deflection itself.
So if I actually knew the formula I would need to insert 30-40 instead of 10-20 for that number and still acheive the same rating of either 360 or 720. Got it. I need a fancy book of tables If I want to figure that stuff.
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Unread 08-25-2008, 06:26 AM   #9
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Is a Mud Job Important to "Dead Load" Calculation ?

I am not sure about the logic of my question - but I'll ask it anyway! It basically involves the consideration that "a mud job has nothing to do with tile floor integrity".

In this forum, I understand that a (deflecto) "floor failure" relates to the consideration of tile cracking etc and not to the structural collapse of the floor. That is, a tiled floor failure would be the failure of the tile installation (in any event, a tiled floor will 'fail' due to excessive deflection well before the structure will collapse due to excessive loads).

In this sense, a tiled floor failure is a separate issue apart from the structural integrity of the floor.

OK, this is my point. The placement of a 'heavy' mud bed (if this is the correct term) on the floor prior to tiling occurs before the tile is laid. The deflection caused by this dead load can not affect tile integrity. If so, this consideration of this dead load component should not come into play when considering tiled floor integrity.

Now, normally, ALL dead loads are important for the structural integrity of a floor (even the dead load of the underlying joists, etc). But none of the dead loads placed on the floor before tiling will affect the tile integrity (insofar as the floor's structural integrity is not threatened - which is a separate issue not directly addressed by the deflection criterion).

This is why there are separate deflection thresholds for variuous types of tile e.g. natural stone, porcelaine, etc).

Perhaps another way of looking at it is: The tile installer can use the deflecto rating to determine tile installation integrity regardless of using a mud job or not. He would not (generally) determine floor structural integrity - a consideratioin beyond the deflecto calculation.

Does this make any sense?
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Unread 08-25-2008, 07:07 AM   #10
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A mortar bed is a dead load of 12 pounds per inch per square foot and must be factored into the load carrying abilities of the structure at L/360 for tile and L/720 for stone.
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Unread 08-25-2008, 08:03 AM   #11
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I would have thought that the mud would be a dead load, Dave. The structure must be capable of supporting it, yes. However, any deflection that is due to the placement of the mud occurs before the tile is set. Therefore, the mud should be considered a dead load. All loads imposed after the tile is set would be live loads.
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Unread 08-25-2008, 08:34 AM   #12
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Dave:
I suppose my comment indicates that floor load capacity and floor deflection are entrely different considerations especially relating to the mortar bed load issue.
As such, the mortar bed load would be factored into the load carrying abilities of the [floor] structure but without any reference at all to the "L/360 for tile and L/720 for stone".
The tile installer would not generally be in a position to determine floor structural integrity anyway as the deflecto calculation/threshold should be (properly) independant of the motar bed loads. (I think that this supports Bob's comments).
So... to take an extreme case: if the floor is qualified to carry a mortar bed of 100 lb/sq.ft., then the tile installer would use the deflecto calculation without regard to the mortar bed loads to determine tile floor integrity. This is because the floor deflection criterion in the deflecto determination should reflect the change in floor deflection after the tile is laid - not the absolute floor deflection due to all floor loads.
I think that this makes sense?

(But, in any case, as I mentioned earlier, loads placed on the floor prior to embedding the tile have no direct impact on the tile failure deflection rating regardless of the load source or magnitude e.g. due to the "heavy" mortar bed. Therefore, for the purposes of installing tile, these loads should be ignored in determining maximum allowable floor deflection. )
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Unread 08-25-2008, 08:52 PM   #13
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Curvature design criteria needs to be for total load is the point I was trying to get across. Plainrider, you can discuss the finer points with Engineer Bob. I am not getting your point.

Here is the tile industry perspective.

Floor systems, including the framing
system and subfloor panels, over
which the tile will be installed using
the appropriate TCNA method (see
page 17) shall be in conformance with
the IRC for residential applications, the
IBC for commercial applications, or
applicable building codes.
Note: The owner should communicate
in writing to the project design professional
and general contractor the
intended use of the tile installation, in
order to enable the project design
professional and general contractor to
make necessary allowances for the
expected live load, concentrated loads,
impact loads, and dead loads including
weight of the tile and setting bed.
The tile installer shall not be responsible
for problems resulting from any
floor framing or subfloor installation
not compliant with applicable building
codes, unless the tile installer or tile
contractor designs and installs the
floor framing or subfloor.
As tile is a “finish” applied to and
relying upon the underlying structure,
an inadequate substructure can cause
a tile failure. In many cases, problems
in the substructure may not be obvious
and the tile installer can not be
expected to discover such.
Proper Spacing Requirement for
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Unread 08-26-2008, 04:50 AM   #14
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Dave, I don't think what you quoted is in conflict with Michael and I are saying. The tile setter is not responsible for the framing, as long as he didn't do the framing. No problem. All loads on the framing have to be considered. Again, no problem. One of the Nits we are picking is where you group the various loads, including the mud bed. If grouped as a dead load, you have a stress and deflection requirement. If you group it as a live load, you have a different deflection requirement. The other Nit is when you apply the load. If the mud bed is placed prior to plastering the ceiling below, it is a dead load. However, if the plaster is already there, then the mud bed becomes a live load.

I think we've said this before: the new TCNA handbook is written around new construction. Remodeling poses it's own problems that the owner, the general contractor, and his subs, must work around.
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Unread 08-26-2008, 05:38 AM   #15
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Dave:
To add to what Bob has said (to which I agree 100%), I would emphasize that the points that we are making have practical implications for the tile installer . As such, this is not simply an "academic" discussion.
Therefore, my 'point' is that an inability to consider this floor-loading "timing' factor can negatively affect home renovation (or even new-construction) decisions regarding floor tile installations.
For one thing, using a criterion for floor deflection that does not take into account "when" floor loads are applied may eliminate the possibility for an otherwise sound and reliable floor tile installation.
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