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Unread 12-01-2002, 09:33 PM   #1
John Joesph
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Join Date: Nov 2002
Location: Southern Ontario, Canada
Posts: 9
Deflection rate calculations

As a newbie I haved learned a great deal from you all.
You all speak of deflection rates. My question is deflection rate calculations. Being known for "overbuilding", I just went ahead and overbuilt when laying in the joists for my last reno, knowing I was going to tile as well as do a shower stall, I fortunatly had bid on and got a number of 2x8'x12's at a real bargain and just went nuts and put them every 12 inches on center for the 8' bathroom and 6" on center for the shower stall and cross braced them all every 3 feet
You all speak of L/x. How is the deflection rate arrived at? What does L represent and how is "x" arrived at.
Having just finished the job, I have been relating how I did it and what I have learned here to others and the question always comes up.
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Unread 12-01-2002, 09:49 PM   #2
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The "L" is the unsupported length of the structural members, expressed in inches. The "x" is a specified number for various allowable deflections.

L/360, for example, is the maximum deflection generally allowed for a tile installation. For some types of tile, it increases to L/480 or L/720.

If you have floor joists that are spanning 14 feet between supports, L/360 permits you to have only .467 inches of deflection at the center of the floor. L/480 would permit only .35 inches, and so on. (14 feet X12 inches = 168 inches divided by 360 = 0.466666). There are other considerations, but that's what the L/x refers to.

Have a look in our world famous Liberry for more information about this and lotsa other stuff. Start here: http://johnbridge.com/vbulletin/show...&threadid=1820
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Unread 12-01-2002, 10:45 PM   #3
Bud Cline
Tile Contractor -- Central Nebraska
Join Date: May 2001
Location: Central Nebraska
Posts: 7,567
The L/720 minimum is for all stone tiles.
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