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Unread 11-16-2010, 07:18 PM   #1
jmallein
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Deflection Calculator

I have a similar build, and I am trying to determine the actual deflection. Specifically, I have 2x6 t&6 (1 5/8x5) set on 4x6s (3 1/2x5 1/4) every 4 feet and posts every 5 feet.

I will be installing 1/2" travertine, and I was planning on using 1/4" hardibacker.

Thanks.
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Unread 11-16-2010, 07:23 PM   #2
Davestone
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What is the spacing between the joists, and do you have two sheets of plywood,equalling at least an inch thick?If you do i think you're fine.
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Unread 11-16-2010, 07:26 PM   #3
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joists are 5' oc with posts every 4'. Currently, there is 3/8 plywood under ceramic tiles, but ideally, I'd like to be able to put the hardibacker right over the 2x6s since I have hardwood in other rooms which is already about a 1/4" lower that the ceramic tiles.

Also, the travertine is 18"

Thanks.
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Last edited by jmallein; 11-16-2010 at 07:51 PM.
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Unread 11-16-2010, 07:55 PM   #4
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The distance between joists,16" or 24".Makes a difference depending on the type of backer you use.Most aren't rated for 24" centers.You cannot put stone over 3/8" plywood let alone over just backer over joists.You must have two layers of plywood and one has to be at least 5/8".
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Unread 11-16-2010, 08:04 PM   #5
jmallein
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Let me try to explain again.

The joists are 4x6 (3 1/2 x 5 1/4) spaced 4 feet oc with posts every 5 feet oc.

On top of the joists are perpendicular 2x6 (1 5/8 x 5) tongue and groove.

On top of the subfloor is 3/8 plywood.

Ideally, I'd like to install the hardibacker directly on the 2x6 t&g, but with a 18" travertine, I am obviously concerned about the deflection and the deflection calculator doesn't have parameters for this 4x6 post and beam construction.

I want to make sure I clear a 720 L deflection.
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Unread 11-16-2010, 08:07 PM   #6
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Thanks Ed.

If that is the case, what the min thickness I can use to reduce the floor transitions as much as possible. I am thinking about using ditra directly on the plywood to help this.
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Unread 11-16-2010, 08:21 PM   #7
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Welcome, JJ.
Quote:
Originally Posted by JJ
set on 4x6s (3 1/2x5 1/4) every 4 feet and posts every 5 feet.
Quote:
Originally Posted by JJ
joists are 5' oc with posts every 4'.
Quote:
Originally Posted by JJ
The joists are 4x6 (3 1/2 x 5 1/4) spaced 4 feet oc with posts every 5 feet oc.
Gotta make up your mind here, eh?

If you have a typical Left Coast construction there, and your beams are, in fact, spaced at four feet on center, and your support posts are spaced at five feet on center, your 2x6 T&G subflooring will be fine for a ceramic tile installation with the installation of a minimum of half-inch exterior glue plywood and the tiling substrate of your choice.

Dunno just what Stoner had in mind up there, but sometimes he just gits that way, eh?

My opinion; worth price charged.
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Unread 11-16-2010, 08:27 PM   #8
jmallein
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Thanks for the help.

The joists are 4' oc with posts every 5'.

What thickness plywood would I need to be able to lay the 18" travertine?

Thanks.
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Unread 11-16-2010, 10:45 PM   #9
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You can't get there from here, JJ.

If you want to use natural stone tiles, you've got to alter your joist structure. You prepared to do that?
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Unread 11-17-2010, 01:03 AM   #10
jmallein
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The wife wants travertine, so I don't really have options.
I saw this under an old thread:
http://www.johnbridge.com/vbulletin/...ad.php?t=12878

Ultimately, I am just trying to determine what my options are. I was trying to get an actual deflection number, so I know where I am starting from. In any event, how does the joist structure need to be altered. Most of the tiling will be in short spans, a 6' wide entry, a hallway and our kitchen, which is 10' wall-to-wall.

Thank you for the help in advance.
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Unread 11-17-2010, 04:57 AM   #11
Davestone
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I totally missed the t&g part.I gotta start wearin my glasses.I think CX is sayin you need more like 24" joist spacing than 4' joist spacing.
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Unread 11-17-2010, 05:16 AM   #12
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JJ, the old thread and your floor are not that different that you can't use the conclusions drawn from it. Your subfloor is more than adequate for porcelain tile, but is just over half as stiff as you need for stone. Add joists to reduce the subfloor span to 24 inches, and add 1/2" of plywood and a tile underlayment, and you can use the travertine the boss wants.

You may have to install beams between the posts so you can install new joists. Make the beams either a nominal 4x6 or use 2 2x6s. A single 2x6 can be used for the new joist. Joist hanger brackets will make this fairly easy.
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Unread 11-17-2010, 11:25 AM   #13
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Thank you for the response.

I know the other thread is very similar, so why was 3/4 plywood sufficient for the same 18" travertine?

The 2x5 t&g attach directly to the 4x6 beams. You mentioned using a 2x6 for the new joist, which is confusing. I am guessing you are suggesting to install cross-beams to the existing beams, so I can hang a 2x6 joist every 24".

Since the posts for a beam are offset from the posts for adjacent beams, I was contemplating a cross-beam every other post, so there would be a cross-beam every 10' with 1 new 2x6 joist attached to the cross-beam. If necessary, I could do a cross-beam for every post, which would create 5' spans for each new 2x6 joists.

Due to the height limitations, I'd rather overkill the beam/joist configuration, so I can use the thinnest plywood under the underlayment.

Is it correct that I cannot attach the hardibacker directly to the 2x5 t&g? If so, then assuming 1/4 hardibacker (or maybe Ditra) what is the thinnest plywood need?

You thoughts would be greatly appreciated
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Unread 11-17-2010, 11:51 AM   #14
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Hardie cannot be installed over the 2x5 planking. Not at all. Needs plywood first, then the Hardie can be screwed down into a troweled thinset bed. There's a few other items you'd wanna watch, such as gapping, orientation, alignment of corners, etc.

And lemme say there's a LOT of really nice, cheap travertine-lookalike ceramics out there which could make your life a lot easier whilst still giving Mrs. JJ the look she desires. Something to look at and show her - mebbe she changes her mind?
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Unread 11-17-2010, 12:29 PM   #15
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The wife likes the philadelphia, so our look-alike options are very limited.
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