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Unread 08-10-2005, 09:54 PM   #1
Trecat
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Joist Span - Deflection

I want to put ceramic tile in my kitchen. My floor joists are 2x10 and 16" apart, and are in good condition. The joists are 13.5 feet long and are supported on each end. In the center, in between each joist is a 2x10 square toenailed to the joist that looks like a divider (l-l-l-l-l-l) and I guess is giving the joists extra stability. Your deflection calc. says 13' foot joists are too long for ceramic tile. Should these extra stabilizers be considered or should I just forget tile altogether? The subfloor is 1/2" plywood with 3/4" particleboard on top. It seems very strong and doesn't move or shake when you walk or run on it. I have been advised to replace the particleboard with plywood if I use tile, and I will provided my floor joists are adequate. Thanks for your help.
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Unread 08-10-2005, 10:03 PM   #2
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I'm confused. I looked at the deflection cal. again and if I choose unknown wood, it tells me 13' joists are no good. But if I choose SY_ or Douglas Fir, it says congratulations. How do I know what kind of wood I have?
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Unread 08-10-2005, 10:07 PM   #3
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Welcome, trecat. Give us a first name to use.

You may be able to find a grade stamp on one of your joists that will help identify them. Aside from that, area of the country, custom, and age of the structure can be helpful. Or go find you an old carpenter and get him to look at them for you. Offer him beer.

The mid-span blocking is good to have and adds stability, but they are not a substitute for adequate joist size.

My opinion; worth price charged.
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Unread 08-11-2005, 09:08 PM   #4
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Thanks for responding. I live in North Alabama and the home was built in 1978. I looked at the stamp on the joist and it says "Rustad's KD, S-P-F, S-Dry 118 No. 3." I tried to look this up and I, believe the SPF stands for spruce, pine, fir, which means nothing to me. The joists actually measure 1.5" x 9. I may just be out of luck for the tile and may have to go to wood or something. Thanks for your help.
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Unread 08-11-2005, 09:18 PM   #5
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Yep, that's what SPF means, (inserts name here when known). Commonly known as whitewood, not a great floor joist material. And not good grade, to boot.

What's the situation under the floor? Could you add a support beam to shorten the span by a couple feet?
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