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Unread 05-02-2003, 05:51 AM   #1
Sierra101
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Question Need Some Help

Hi

I need some advice, I would like to install 12'' x 12" ceramic tiles in my entryway and kitchen approx. 500 sq. Ft. The home is a single story custom built in the mid 70's, the entryway currently has ceramic tiles installed that are original, which I'm going to remove, but I have some concerns about the existing subfloor the dimension are as follows.

4x6 Joist Spaced 40 inches O.C.

Metal Support Columns (That's probably not the right name for them) running from the 4x6 Joist's into the dirt foundation.

1 ½ inch T&G Plywood.

The Plywood subfloor is in good shape & seems pretty solid, there were two layers of existing linoleum attach to particle board which I already pulled up. I'm planning on putting wonderboard down, I need to know if you think the subfloor is sufficient enough? or does it need to be reinforced, if it does how would you go about reinforcing it? With all of the added weight of the backerboard & tiles I'm really concerned the tiles or grout might crack. I greatly appreciate any advice you can give me on this situation.

Thanks

Last edited by Sierra101; 05-02-2003 at 08:13 AM.
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Unread 05-02-2003, 03:20 PM   #2
John Bridge
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Welcome abaord, Sierra.

We've been through this, but I can't remember what the outcome was. On top of that, our chief engineer is goofing off down in Jamaica this week.

The largest concern, the way I see it, is deflection between the joists. I'm not too worried about your joists, being that they are supported with the steel beams. 40 in. is too much span, even for 1-1/2 in. of plywood. I think I would install some short joists perpendicular to the 4x6s, say every 16 in. I'm talking about an arrangement that would resemble a ladder when you've finished.

Others will be along to shoot me out of the saddle.
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Unread 05-02-2003, 06:12 PM   #3
tileguytodd
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If i am reading this correctly i think he has the adjustable support posts going into dirt with no footing underneath.perhaps not a problem in california but a big no no up in the frozen tundra

Now as far as the 40" spread goes with 1 1/2" of plywood,i have to agree with John that the deflection amount would be too much.The additional joists like john described would really help shore things up and actually shouldnt be too difficult .They are short pieces and with joist hangers it wouldnt take long at all.

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Unread 05-02-2003, 11:37 PM   #4
Sierra101
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Question

John & Todd thanks again for answering my questions, I really appreciate your advice, here is some further info on the situation, I went further into the crawl space today and found out some parts of the floors were reinforced with 2x4's that run perpendicular to the joists they are spaced around 20' O.C. I will go ahead and reinforce the other parts of the floor with 2x4's w/ joist hangers spaced 16 inches O.C. but before I do that I have few more questions,

1. Will 2x4's be sufficent enough to do the job ??
2. After I install the new joist will I have to nail the Plywood subfloor above into the new joists to secure them better ??

I have no idea why the house was designed like this , the original owner was a General Contractor, he designed and built the house.

Any advice would be helpful.

Last edited by Sierra101; 05-03-2003 at 03:19 AM.
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Unread 05-03-2003, 05:09 AM   #5
tileguytodd
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While a 2x4 may help it doesnt really have a lot of structural beef to it.I would jump up to a 2x6 myself.You do not want to nail your plywood into these supports.these are just to insure against deflection(or sagging of the floor with several people standing in the middle of it)Hows that for laymans terms You do want them to be put in from underneath snug to the floor above it. a couple blocks of wood and a hydraulic jack will free up your hands and get things snug.Just snug.dont jack up the floor though
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Unread 05-03-2003, 06:29 AM   #6
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I'm no Bob Camp, but the deflectolator says 2x4's of the highest grade, 4 foot length at 16" oc gives L / 754. Second grade even gives L / 577, so they should be enough. But my advice would be to wait for Bob to get back from Jamaica or go to 2x6.
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Unread 05-04-2003, 06:43 AM   #7
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I have a philosophy about that that has never failed me Dave,
2x4's are for interior walls other than that if ya wanna build something, put some real wood in it
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Unread 05-04-2003, 09:31 PM   #8
Sierra101
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Thumbs up

Thanks for all of your help...

I will go ahead and use the 2x6's instead of 2x4's.
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Unread 05-05-2003, 10:03 AM   #9
bbcamp
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Either will do. Although, I'm not sure why we wouldn't want to secure the joist to the plywood subfloor, except for that "don't nail the top layer to the joist" rule. You can use construction adhesive so there will not be any squeaks. Also, a little "crown" on the joists (crown side up) would make sure the joists are supporting the subfloor and not just hanging there doing nothing.
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