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Unread 05-05-2021, 10:28 AM   #1
MarkK
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Deflecto question

New member here. I found this forum and it looked useful (and friendly) so decided to join. The decision was helped along by a flooring job my wife and I want to do in our rental.

The rental is a late 60s ranch with the old tongue and groove subfloor. The floor we removed was vinyl, fortunately asbesos-free (so most likely NOT the original 60s-era floor), and we want to install tile. Hence my interest in the deflection calculator. Deflecto requires some parameters related to the joists, and that's where my first question on this forum stems from.

The joists are supported on posts on a 4 x 8 foot grid, with the joists spaced 4 feet apart. Should I enter 4 feet or 8 feet into the Deflecto tool? We want to get this right so the tile doesn't fail down the road.

Thanks!
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Unread 05-05-2021, 02:17 PM   #2
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Welcome, Mark.

If you'll put a geographic location into your User Profile, we'll know where on the Left Coast to look for you and we'll likely be familiar with your type of floor construction.

The "old tongue and groove subfloor" is perhaps nominal 2x6 boards, perhaps?

Let's start there.
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Unread 05-09-2021, 10:24 AM   #3
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I have fleshed out my profile to give folks a little more background about us.

Regarding the question about the T&G subfloor, yes, they are 2x6. They were installed at right angles to the joists, not diagonal, so they are as short as they can possibly be.

I checked the floor with a 4 ft builders level and it looks pretty flat. The kitchen/DR is 8 ft deep by 16 ft wide, with the long axis parallel to the joists. A joist runs right down the middle of the floor so the spans are 4 ft on either side. I haven't gotten close enough (yet) via the crawlspace to see where the joist supports are in that part of the house.
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Unread 05-09-2021, 11:33 AM   #4
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That floor construction style is apparently common all along the Left Coast and our resident engineers have determined that the subfloor is sufficiently rigid for a ceramic tile installation, so long as the joists are of sufficient size and material and are supported at appropriate lengths. We don't have any information on that part as yet, eh? Seems they're most commonly nominal 4x6 beams and as such must have unsupported span of no more than 7 feet.

On top of the "car plank" subfloor you must install a minimum of nominal 1/2" exterior glue plywood with no face of grade lower than C. Then the tile installation substrate of your choice and your ceramic tile.

My opinion; worth price charged.
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Unread 05-09-2021, 11:36 AM   #5
MarkK
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Beams, joists and subfloors. It's possible that our rental doesn't have joists, just T&G on top of beams -- see attached photo, taken from the crawlspace looking up at the subfloor. That could explain why I can't enter info for our situation (maximum joist spacing is 24", while the beams are 48"). Not sure how this affects the Deflecto calculation, if it can even handle this particular case.
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Unread 05-09-2021, 11:45 AM   #6
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The Deflectometer can deal with your situation, Mark, but you hafta tailor the input to its tastes.

Those beams are your joists. If they are nominal 4x material, you would enter their size as 2x material at 24" joist spacing and the calculation would be correct.

Again, you need the size, species, and unsupported span of those beams.

My opinion; worth price charged.
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Unread 05-09-2021, 12:05 PM   #7
MarkK
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It appears that our floor is rigid enough for both tile and natural stone. Since we're going to use ceramic tile we should have a pretty comfortable design margin. As an ex-engineer I like that .

Installing 1/2" plywood with CBU on top will require a transition piece where the tile meets our oak floor, but sobeit. We don't want the floor to fail when there's a tenant in there.

Thank you for your quick responses, much appreciated!
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Unread 05-09-2021, 01:49 PM   #8
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Your subflooring is not suitable for natural stone, Mark, only ceramic.

You can decrease your transition height just a little by using one of the sheet membranes rather than 1/4" CBU if you want.

My opinion; worth price charged
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Unread 05-09-2021, 08:18 PM   #9
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Welcome, Mark.

If you’re interested in saving height by using a membrane instead of cement board, as CX suggests, perhaps you might consider NobleSeal CIS, as it’s only .03” thick.

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