Replies

1. 
   Velmason | Feb 02, 2003 07:38am | #1

   My span tables for floor joists shows #2 Douglas fir 2 x 8's will span 11' 3" at 24" on center, and 13'1" at 16" o.c. , based on 40Lbs per sq ft. live load plus 10 psf dead load. As the wall tiles will not be carried entirely by the floor joists, I would think the only area of conern is the 4 x 4 shower base. If this will exceed 10 psf you may want to sister up the joists under it. If the joists are of a different wood species, or you need more than 40 psf. live load design then you should check other tables or with an engineer.

1. 
   rjw | Feb 02, 2003 08:00am | #2

   But with tile floors, you don't just do a load calculation, you have to have a stiffer floor to prevernt cracked tiles.

   _______________________

   "I may have said the same thing before... But my explanation, I am sure, will always be different."  Oscar Wilde

1. 
   Piffin | Feb 02, 2003 08:17am | #3

   Right Bob, in other words, read the tables for less deflection.

   Span calc doesn't have choices for better than L-360 so I chose heavier load rating and it still looked ok..

   Excellence is its own reward!

1. 
   rjw | Feb 02, 2003 01:22pm | #4

   For some reason, this is a hard concept for many folks to follow - at least based on the blank faces I've seen while trying to explain it.

   Now I say: "Wood floors always have a little bit of flex and bounce in them, that's why they are more comfortable than concrete floors.  Ceramic tiles don't have a sense of humor, let 'em flex a tiny bit and you get [or "might get"] the [hairline] cracks we're seeing."

   After a couple of thousand houses, I know where to expect floor tile; when I see it where I don't expect it, I know to look for cracks (and that they will be easy to find.)

   I wonder if HD teaches this stuff in their DIY floor tile course?_______________________

   "I may have said the same thing before... But my explanation, I am sure, will always be different."  Oscar Wilde

2. 
   CAGIV | Feb 03, 2003 09:02am | #9

   where did you get that neet looking calculator?

1. 
   Piffin | Feb 03, 2003 02:08pm | #10

   Free download here

   https://secure.cwc.ca/cwc.ca/design/design_tools/spanc112.html.

   Excellence is its own reward!

3. 
   Catskinner | Feb 05, 2003 06:49pm | #15

   Hey Piffin,

   Wher'd you get that span calculation gizmo? Looks handy.

   DRC

1. 
   toolnut | Feb 05, 2003 06:58pm | #16

   see post 11.

2. 
   CAGIV | Feb 06, 2003 01:54am | #17

   I asked the same question, heres the link

   https://secure.cwc.ca/cwc.ca/design/design_tools/spanc112.html

2. 
   BossHog | Feb 02, 2003 03:21pm | #5

   How far do the floor joists span?

   BTW - You can take the floor span from the table at 24" O.C., and double it if you're using the joists 12" O.C. Or increase it 50% for 16" O.C.

   Bumpersticker: "So many pedestrians, so little time."

1. 
   deblacksmith | Feb 02, 2003 04:07pm | #6

   I assume you mean that you can double the LOAD and not the span when you change from 24" centers to 12" centers.

   Just checking.

   Deblacksmith

1. 
   BossHog | Feb 02, 2003 09:04pm | #7

   You're right - The loading will double, not the span.

   I was probably not concentrating when I was typing that one, as I had just read the thread about breast implants...............(-:My kid knocked up your honor student.

1. 
   Piffin | Feb 02, 2003 09:36pm | #8

   I see the connection.

   Cleavage

   Cracks

   Bounce

   Vibration

   It all runs together after awhile....

   ;-).

   Excellence is its own reward!

2. 
   JohnSprung | Feb 05, 2003 04:37am | #11

   Right, either multiply the load by 2, or multiply the span by 1.41 (square root of two).

   -- J.S.

1. 
   leaninlouey | Feb 05, 2003 04:54am | #12

   Thanks for the great ideas, here is what i decided to do. I have a 10' span on the 2x8 floor joists, with 1/2" ply on that, Added 3/4" ply over that. Put a double 2x10 header with 3/4 ply between em at the five foot mark under the floor in the basement. Went over both layers of flooring with 5/8" cement board.

   Sound stiff?  Thanks again, Redo-it.....

3. 
   hammerhead | Feb 05, 2003 05:01am | #13

   Yes the floor must flex {trampoline effect}, and yes your design load should be L/600, but if you do not want cracks use an isolation membrane-either brush on or membrane style.

4. 
   andybuildz | Feb 05, 2003 01:05pm | #14

   Not that this will help you at this point but for the future.....Anytime I build a bathroom I "always" use dbl 2x's 12" OC. The added wood goes a long way for minimum cost. Plumbers get pizzed but then again they usually butcher my work anyway (kidding.sorta).

   Then again I usually overdo things

   Be safe

            Namaste

                       andy

   "Attachment is the strongest block to realization"
   http://CLIFFORDRENOVATIONS.COM