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Unread 02-10-2008, 11:29 PM   #1
67stang
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Help understanding Deflection calculator

Hi there
I'm prepping to tile my bathroom floor and am trying to understand if the current subfloor will be sufficient with porcelin 12x12 tile.

The subfloor in this 1952 house is 2x6" (nominal. actual measures approx 1.5" x 5.5"), they are about 12.5" apart on center. Pic below gives a slight confirmation. 3/4" plywood on top.

Using the Deflecto calculator I am getting L-310 and consquently a thumbs down on using tile. The thing I do not understand is that the calculator does not seem to take into factor the thickness of the plywood.

So, with the 3/4" ply plus a mortar bed and 1/4" Hardi will I be ok?

Thanks
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Unread 02-11-2008, 02:32 AM   #2
Deckert
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Did't see it above, whats your unsupported span on those joists?
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Unread 02-11-2008, 06:54 AM   #3
John Bridge
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Hi all,

Looks to me like there might be a supporting wall under there.

On bathroom floors, unless they are very large, I recommend the jump test. In other words, if the floor is really sturdy, it'll work, especially with mud float.
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Unread 02-11-2008, 11:04 AM   #4
67stang
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Whoa - John Bridge! I'm honored to get a reply from the master himself! Thank you. Now - what do you exactly look/feel for in his jump test? I know it is probably intuitive, but I am not sure how you objectively tell if the floor is solid or not by jumping on it?

With respect to longest span, I do not know since I cannot see that far under the home. I suspect the span is not more than 10 ft since I can actually see just under that hole there is a thick (4x4 or so) piece of redwood perpendicular to the the joists. I figure there has to be one 10ft or less in the other direction since there is a load bearing wall between the bathroom and kitchen.

bathroom is only 5ft wide, wall to wall, in the direction of the joists,.
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Unread 02-11-2008, 01:39 PM   #5
Maack
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jump test

The jump test is simply a*possible* indication of basically how stiff a floor structure is..

It is a pro's first indication of wether or not the floor is *really solid* or really bouncy,or in between somewhere.

Jump on a concrete sidewalk, that's as tough and ridgid as you can get.

(basically just raise up on your toes and let your heels come down hard)

Then jump on a kitchen floor for instance , one that has a floor structure that spans over a basement or crawl space .
You will most likely notice some *bounce* with the kitchen floor.
Comparing that to other*bounce* floors and you will have a sense of what constitutes ridgid as opposed to slighty bouncy, more bouncy, etc.

It's really just an *educated guess* at the rigidity of the floor that pros use to get a first sense of the structure strength. a*first indicator* if you will..

good luck...
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