Deflection help [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-14-2019, 10:33 PM
Hey all taking a shot at DIY my kitchen floors. Situation is 1910 foursquare home. Kitchen has loop 0hardwood subfloor with 3/4in plywood on top. Beam in center of home with 2 posts. Joists are 26.5 ft long. Kitchen is 9 x 11. I want to do 8 x 24 in ceramics on ditra for transitional height. What can I do to beef up, if possible? I put 13.5 ft long between joists the correct input in the calc? Deflecto info:

Thank you for using the John Bridge Forums Deflect-O-Lator :-)

For joists that are Unknown wood, but in good condition, 9 inches tall, 1.5 inches wide, 14 inches on center, and 13.5 feet long between supports, the deflection calculated is 0.477 inches.

This translates to a deflection of L / 340.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Sheet Vinyl or wood.

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07-15-2019, 04:53 AM
Hi James,

You are very close to the require stiffness level. I’d go inspect the framing to determine the wood type. You’ll likely not find grade marks but try to inspect all of the material to ensure it is equivalent to #2 with tight knots.

Most framing of that age is full 2” thick so I recommend you double check the height and width. Same for the unsupported span.

Let me know what you find.

07-15-2019, 07:11 AM
Welcome, James. :)

It's also unlikely that your joists are on 14" centers. More likely to be 16" on center. Check that, too.

07-15-2019, 07:22 AM
Thanks for the replies. I will double check measurements. I think I fudged the on center and just measured between the joists, which was 14in. If the joists are 2 in thick I will assume it will actually be 16, which will mean my deflection is worse. I will remeasure and take a few pics if this lets me post them. Appreciate it.

07-16-2019, 11:55 AM
If the joists are 2 in thick I will assume it will actually be 16, which will mean my deflection is worse.

Maybe not, the extra 1/2" of width makes for a stronger joist and will more that offset the 16" joist spacing. Double check all of your measurements and let's see what the next step should be. :)

07-16-2019, 03:09 PM
I bet that 1910 true 2 by is some strong good material that's better than anything listed in the deflecto calculator 11 I had to replace a subfloor in the bathroom ou f a 1929 pier and beam home. The joists were hard like a rock. Forget about nailing into the them. There are diagonal 1 by 6 s as a subfloor and the bedroom portion of the house had Pine flooring on top of that and the other half of the house for the living and dining room had oak flooring and then the walls were built on this platform I don't know how they could have this wood exposed in Houston before they could get the house dried in

07-16-2019, 05:35 PM
Not real sure just how any of that might apply to the OP's situation, Teddy, and joist hardness doesn't necessarily equate to stiffness. Where I grew up lots of the old structures were framed with oak. Hard as Chinese algebra, but not particularly high on the deflection scale.

07-16-2019, 05:54 PM
Hard as Chinese algebra