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Unread 02-14-2021, 01:54 PM   #1
Charash1414
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No more L/360???

In researching whether a potential client's floor can accommodate tile, I found that their deflection is less than L/360. In my attempt to best explain this problem, I came across an FAQ from TCNA that states the following:
"Recent research has shown tile to fail, under some conditions, when the floor is more rigid than L/360. In fact, failures at L/600 have been observed. It is for this reason that recommendations for floor rigidity are not based on deflection measurements but on empirically established methods found to work over normal code construction."
Does this mean that the L/360 criteria does not apply as long as we are using established methods, which for the most part, require L/360?
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Unread 02-14-2021, 03:53 PM   #2
cx
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Quote:
Originally Posted by TCNA
What is the acceptable deflection for a floor that will be tiled?

Traditionally, the accepted minimum requirement for floor rigidity is L/360 - before the tile underlayment is installed. The L/360 standard means that the floor should not deflect more than the "span" divided by 360. If the span of the joists is 10 feet (between supports), then the deflection should not be more than 1/3" between the center and the end. Frequently, there is misunderstanding regarding deflection between joists. For example, while joist manufacturers regularly meet the standard L/360 criteria for code construction with 24" o.c. (on center) systems, these floors often have deflection between the joists exceeding L/360.

Recent research has shown tile to fail, under some conditions, when the floor is more rigid than L/360. In fact, failures at L/600 have been observed. It is for this reason that recommendations for floor rigidity are not based on deflection measurements but on empirically established methods found to work over normal code construction.
That TCNA response, taken in its entirety, Travis, seems to me to be indicating the problems you can have with between joist deflection. It's not particularly clear, but that's my take on it, 'specially since it indicates the "established method" being over "normal code construction," which would be the joist deflection of L/360. There is no "normal code" requirement for subfloor deflection that I'm aware of.
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Unread 02-15-2021, 11:00 AM   #3
Dave Gobis
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The curvature of between the joist is what they are referring to. The bigger the tile the greater the potential for issue is the way it seems to play out. I have not been in on any recent study but there was a substantial amount done when I was still around. The subfloor is critical to performance.
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