will floor joists make me or break me?
I have a customer with 2×8 floor joists in a 10×10 bath and i am a little conserned whether they will support the load of full wall ceramic tiles, floor tiles as well as a custom mortar and tile shower area of 4×4 not to mention fixtures all in this area. The outside wall is supported by the foundation, the opposite wall is supported by the center header and posts running down the middle of the basement. These joists have metal bridging in place already, and look to be in good shape.
Replies
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.
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
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!
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
where did you get that neet looking calculator?
Free download here
https://secure.cwc.ca/cwc.ca/design/design_tools/spanc112.html.
Excellence is its own reward!
Hey Piffin,
Wher'd you get that span calculation gizmo? Looks handy.
DRC
see post 11.
I asked the same question, heres the link
https://secure.cwc.ca/cwc.ca/design/design_tools/spanc112.html
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."
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
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.
I see the connection.
Cleavage
Cracks
Bounce
Vibration
It all runs together after awhile....
;-).
Excellence is its own reward!
Right, either multiply the load by 2, or multiply the span by 1.41 (square root of two).
-- J.S.
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.....
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.
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