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Old 03-13-2012, 08:13 PM   #1
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Securing plank subfloor to joists?


I have purchased some #10 2" screws to attach our t&g plank subfloor before tiling.

How often do I need to screw the planks into the floor joists? Joists are 16" oc and planks are 3-1/4" wide. So, screwing every other plank would mean a screw every 6-1/2". Is this adequate, overkill, or a good plan?

1/2" ply to go over t&g, attached with #8 1-1/4" screws, then Ditra, then the tile. I've received advice on amount/spacing of the 1-1/4" screws, but not the 2".

Oh yes, I consulted the Ditra handbook, which was helpful regarding the method, but said nothing about how often to screw the t&g.

Thanks to everybody for your help!

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Old 03-13-2012, 08:23 PM   #2
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Securing plank subfloor to joists?


Why in the world would you ever use planks and not Just use T & G Advantec subflooring? Far smoother, 0 chance of it cupping, far easer to install, 50 year warrenty.
I use ceramic coated decking screws installed with an impact screw gun with constrution adhesive on the joist and install the screws every 6".

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Old 03-13-2012, 08:41 PM   #3
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Securing plank subfloor to joists?


I did basically the same installation about a month ago (my boards are 4.5" wide and 3/4" thick). I put two screws in every board at each joists. Overkill? maybe, but I bought a bucket of 4300 screws so I was going to use them! I screwed the plywood (also 3/4") down 6" oc, sometimes 4" oc if it was a high traffic area using the same screws as the subfloor (1 1/4").

Be sure to buy extra thinset, as filling in those waffles in the ditra takes a lot!
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Old 03-13-2012, 08:56 PM   #4
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Securing plank subfloor to joists?


Duffman,

It would have been better if you had added this question to your original thread concerning this project. All the info is there, but OK.

Absolutely, you need 2 screws at every joists and it's not overkill. I have not idea either why you'd consider skipping a plank.

Shazapple,

The 1 1/4" screws you used to fasten the subfloor to the joists are too short. Good luck with that.

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Old 03-13-2012, 09:16 PM   #5
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Securing plank subfloor to joists?


Joecaption - I didn't choose this flooring, it's what was there.


Am I getting this right? Two screws per plank, per joist? Basically one screw every 1-3/4" along the joist? Never would have dreamed I needed TWO per plank, and yes, every other plank seemed like it could be a bad idea... Glad I asked!
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Old 03-13-2012, 09:28 PM   #6
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Securing plank subfloor to joists?


See...........
Quote:
Joecaption - I didn't choose this flooring, it's what was there.
Exactly the reason not to start a new thread. That info is in the original and Joe would have known.

Quote:
Two screws per plank, per joist? Basically one screw every 1-3/4" along the joist?
1 3/4" is not relevant, if the boards were 2", the screw might be 3/4" apart. You need two per plank to help prevent the boards from cupping. With wider boards I have used 3 screws at times.

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Old 03-13-2012, 09:40 PM   #7
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Securing plank subfloor to joists?


"Oh yes, I consulted the Ditra handbook, which was helpful regarding the method, but said nothing about how often to screw the t&g."---- because sub-flooring should be nailed, per minimum code:
24 1" 6" subfloor or less to each joist, face nail 2-8d (21/2" 0.113")
2 staples 13/4"
From: http://publicecodes.citation.com/ico...002_par005.htm

Underlayment: http://www.apawood.org/pablog/index....-Floor-Systems

http://www.apa-europe.org/Languages/.../PDF/R340G.pdf

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Old 03-13-2012, 10:56 PM   #8
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Securing plank subfloor to joists?


Quote:
Originally Posted by duffman56 View Post
1/2" ply to go over t&g, attached with #8 1-1/4" screws, then Ditra, then the tile. I've received advice on amount/spacing of the 1-1/4" screws, but not the 2".
Plywood is 1/2 inch, t&g is 3/4 inch, that means that the screws that you're planning to use will barely make it through to the joists, if they even break out the back at all.

I wouldn't use anything shorter than 2"
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Old 03-14-2012, 06:22 AM   #9
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Securing plank subfloor to joists?


It sounds like the op meant using 1 1/4 screws for tile spacing?.....
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Old 03-14-2012, 07:09 AM   #10
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Securing plank subfloor to joists?


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It sounds like the op meant using 1 1/4 screws for tile spacing?.....
Maybe, but that's not how I read it:
Quote:
1/2" ply to go over t&g, attached with #8 1-1/4" screws, then Ditra, then the tile.
I understood that to mean that the 1/2 inch ply was to be attached to the t&g with the 1 1/4 screws. But it sounds like there are two threads on the same topic (not that I've ever been guilty of that. ) so you may be reading with other info that I don't have.

When I did the kitchen floor in my last house, I screwed the t&g to the joists with 2 inch screws, then screwed the ply through the T&G with 2 1/2 inch screws. I used shorter screws for the hardi backer layer, but at that point I had raised the level of the floor close to an inch (ply, SLU, hardi backer) so I figured that if it was still going to shift/bounce there was nothing I could do about it.
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Old 03-14-2012, 08:24 AM   #11
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Securing plank subfloor to joists?


You are not supposed to screw the plywood through the t&g to the joists. I don't remember the reason but that was one of the things mentioned in the TCA underlayment document.

I'm not too worried about the length of screws I used for my planks, but longer probably would be better.
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Old 03-14-2012, 08:34 AM   #12
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Securing plank subfloor to joists?


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You are not supposed to screw the plywood through the t&g to the joists. I don't remember the reason but that was one of the things mentioned in the TCA underlayment document.
Huh, I wonder why. We'll have to wait for an expert to answer that one.

I was told specifically to do it the way I did it by a floor contractor.
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Old 03-14-2012, 08:48 AM   #13
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Securing plank subfloor to joists?


Yes, I am guilty of starting a new thread on the same topic. I only did so to generate some answers, as the other thread seemed to of died before my questions regarding the joist screws were answered, and I am wanting to have the floor ready for tile this weekend (working on it every night after work). For that I am sorry.

The #8 1-1/4" screws are not intended to go into the joists, only to secure 1/2" ply to the t&g.

The #10 2" screws are to go through the t&g and joists only. Given that I will be putting the screws so close together, and two per plank, are these screws too beefy? Should I use #8s instead?

I had looked for "flooring screws" but couldn't find anything by that name. The screws I did purchase are #10 2" Spax Construction screws ("For Multiple Materials"). I thought the fact that no pre-drilling was required would be beneficial.

Is there another size/type of screw that would work better, or should I go ahead and purchase more of these? Thank you all for your help (obviously I am very green at this), and again - sorry for starting a new thread.
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Old 03-14-2012, 09:33 AM   #14
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Securing plank subfloor to joists?


The 1 1/4 screws won't hold your ply to the plank floor use 2 1/2 or 2 5/8 either deckmate screws or very corse sheetrock screws but galvanized screws would be better to use for these sizes for both 1st and 2nd layers.

I don't think screwing in the t&g will be a good idea as its a week spot in the wood your also putting 1/2 on top so any chances of it cupping are very slim.
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Old 03-14-2012, 10:30 AM   #15
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Securing plank subfloor to joists?


Not that I'm an expert, but as I've seen on DIYTV...you screw the subfloor to the floor joists...then the sheeting over that does not get screwed to the floor joists, but to the subfloor. What I've been told is 6" on perimeter and 8" in the field should be good.

So, 2 inch screws will work for the TG subfloor, and then 1-1/4" will work for the half inch sheeting. The 1-1/4" screws that you are using will penetrate the TG subfloor to the full thickness of the TG, especially if you drive them in so that the heads are countersunk slightly.

The reason that you don't want to skip boards is that you will essentially have a floating floor where you don't have any screws...and movement, and squeeking...not good. So, like was said, 2 screws per board...and I'd also consider gluing them to the floor joists. And, don't forget to block around the edges for support. The old TG or whatever the subflooring was, extended over the rim joist and under the wall's and on top of the floor joists. When you cut out the subfloor, you need to block the edges so that you will have a nailer around the perimeter of your new TG subfloor for support. Sometime this little bit of information is overlooked.

I did some research in a couple of other DIY forums...it appears that it's not recommended that underlayment, like plywood, be glued to the subfloor...your TG.

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Last edited by Ed911; 03-14-2012 at 11:06 AM.
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