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Unread 11-07-2003, 10:30 PM   #1
Pledget
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Joist span and size

I'm remodeling a bathroom above a crawlspace...home built in '72...joists 2"x12" and 16" OC...Will the dimesions of the joists and the span between them be adequate for a ceramic tile shower (with mortar floor and sloped subfloor and CBU underlayment for walls)?

Thanks.
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Unread 11-08-2003, 12:49 AM   #2
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Depends on how long the joists are between supports. That'll give you an idea how much deflection you're looking at in the joist structure. Mostly a consideration if you're gonna tile the floor, but would be good to know before you start the shower anyway. The spacing between the joists is fine.

What do you have over the joists thus far?
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Unread 11-08-2003, 01:28 AM   #3
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Ple...

If you can, measure the overall span of the 2x12's. How far between supports. Then you can enter all that info into our "deflectometer" in the top right hand corner of this page. That will tell you how much a load you can stand.

Let's start there, the you get back, OK?

My name (as indicated by my handle) is Sonnie.
What do we call you?

Take a look at the deflecto and you'll see exactly what kind of info is needed. I've got a feeling you're gonna be good, but it's always best to know from the beginning, right?

Welcome to mortardom.
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Unread 11-08-2003, 09:36 AM   #4
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Thanks, guys. I'll obtain more info and get back to you...

Sonnie, you can call me Victor.
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Unread 11-08-2003, 04:59 PM   #5
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Joists are not as wide as previously envisioned...1 1/2" x 9 1/4" x 12' 9 1/2"..nmbers plugged into deflecto...thumbs up ceramic tile but thumbs down natural stone (I'm using travetine and durango to cover entire floor of bathroom and shower and shower walls)...would sistering or sandwiching joist be adequate? Note, I believe the joists are fir and 16" OC. Bathroom is 6x12 and shower stall is about 4x6.

Thanks,
Victor
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Unread 11-08-2003, 05:31 PM   #6
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That's a more standard sounding floor, there, Victor. Yes, sistering joists will get you where you wanna go. Probably don't need the full 2x10s for the sisters, I'm reasonably sure your could use 2x8s and possibly 2x6's near the bottom of the existing, but we'd hafta get Bob to approve any of that.

Depending upon the layout under your floor, adding a beam perpendicular to the joists to reduce the span may be easier than sistering. Sometimes you can get more bang for your buck that way. Best at the center of the span, but you only need to reduce your span three feet or so if that would be more convenient.

How much crawl space you got under there?
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Unread 11-13-2003, 07:17 PM   #7
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Sorry CX..been on vacation in sunny Ohio...
Crawl space is about 3 feet high, 12' wide and about 80 feet long...my very own rock filled bowling alley...

I'm toying with to seperate approaches:

1: sistering joists under bathroom.

Questions: sister all joists under bathroom or a select few?
sister the joists the entire span (13') or some
fraction of the total length of the existing
joists?
if need to sister the entire length of joists can I
rip sistering joist in half (for ease of
placement) then overlap this joint on opposite
side of floor joist with another sister?

2: place support beam perpendicular to joists under bathroom.

Questions: How to hold beam in place...abutments
(Jacks/4x4's) placed on cement footer?

Thanks!

"I don't know alot, but what I do know I can't remember."
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Unread 11-13-2003, 08:25 PM   #8
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Vic,

Might there be a way of bolting beam hangers into the foundation wall? These are "U" shaped things that look like joist hangers only beefier.

Is "beefier" a word?

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Unread 11-13-2003, 08:31 PM   #9
Sonnie Layne
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hmmm....... maybe "bullier" ???
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Unread 11-13-2003, 09:17 PM   #10
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Welcome back, Victor.

You really want to sister the full length if possible, a little less still gains you a lot, but full is best.

No, you can't rip the sisters for ease of installation - this ain't s'posta be easy, it's s'posta be did right. You don't wanna cut them in half, either. Now, it's possible that you don't need full 2x10 sisters under there. As I said before, you can probably get by with 2x8s, which would make the installation easier by a lot. We gotta let Injineer Bob make that call though. And yes, you would hafta do all the joists in the area of your tile floor if at all possible, and a little beyond would be my recommendation.

If you elect to do a perpendicular beam, you would need it to be supported on concrete footings dug into the undisturbed earth below unless you can attach both ends to some existing structure. PITA with only three feet of working room, but that's what you gotta do.

JB's suggestion of the joist hangers may be easier than sistering if you install new joists between the existing that way. Some other considerations if you chose that method so's not to introduce any squeaks.

Or some of them beefier things. Or porkier. Or whatever.
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Unread 11-13-2003, 10:50 PM   #11
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Lots o' supply lines, drain lines, electrical conduit and air ducts in crawl space fixin' to make the job problematic...I guess if it were easy it wouldn't be a job now would it? I'm not certain even without the "accessories" in the crawl space how I would place the sister joist into position seeing that space available for maneuvering is 12' 8" and joist length is 12' 8" with 16" OC spacing and half the floor above finished with hardwood flooring and closet space.

Placing a perpendicular beam would solve alot of issues, however this seems more like a "patch job" (no offense-I'm still learning) than a permanent fix. Plus, the dificulty in digging the footings in limited crawlspace is not welcoming (note, no convenient place to hang beam since the span in this plane is 80' and bathroom in middle of this span).

I think maybe a hybrid of the two ideas could be effective...sister joists under bathroom (about half the length of existing joists and place perpendicular beam at free end of sister joist...overkill or too beefy (beefier?)

probably easiest to sister joists if I can remove obstacles and learn how to maneuver them into place...

sorry, just thinking out loud and apparently documenting in the written word...any ideas or comments? any other options?

Good to be back amongst the professionals!
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Unread 11-13-2003, 11:17 PM   #12
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If you've got a lot of junk under there to deal with, Victor, the center beam does make the most sense. And no, that's not at all a patch job if done correctly, it's quite permanent and you will stiffen the floor above much more than with the other methods. Halving the span of your existing joists will provide a rock-solid base for your stone flooring.

Digging the holes under there won't be any picnic, for sure. Are you in an area with a serious frost line? Like, did you hafta go north or south to vacation in sunny Ohio?

If frost isn't a serious consideration, you only need to get half a foot or so into undisturbed soil (more is better) and get you a large footprint, like at least two feet square. But then you gotta get some cee-ment in there, too. You hafta go the whole 40 feet to get to the middle?

If you can't get maybe ten foot sisters on all those joists (how many we talking about?), I think I'd get out my short shovel and pretend I knew where there was some gold burried under there.

Then we'll get Bob to say how much beam you hafta build after you say how far it's gonna be betwix them pads.
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Unread 11-14-2003, 06:28 AM   #13
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You only have to put the beam under the tiled area, so at most, it will be about 12 feet long. If you make you beam out of 2 2x8s and space the posts 6 feet apart, you should be fine.


I think you already ruled out sistering the joists. That's good, since they will have to be 2x10s.
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Unread 11-14-2003, 03:25 PM   #14
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About 12 joists under bathroom...have ample room for beam under 7 of the joists on one side of the room and 1 on other side...conduit/pipes prevent placement of beam under others.

Evaluation of crawlspace reveals that a beam could be placed under the joists (under whirlpool tub and shower) 8' from foundation so joist span would be 8' instead of 13'. Deflectometer indicates this would be O.K. for natural stone, however, would sistering these joists help the cause or would it be a waste of my time?

If I placed beam here would I need another on opposite side of bathroom and have it overlap with joists of adjoining room or would this one beam be sufficient?

By the way, I traveled laterally to get to Ohio...I'm in the mid-midwest

Sure seems like planning of alot of extra beef..previous bathroom had 1 1/2" mortar floor with ceramic tile and ceramic tile shower (30" x30") walls. Does natural stone REALLY weighuch more than ceramic or is the extra beef under the floor necessary to prevent flexing/movement of floor? Natural stone (travertine in this case) is probably much more brittle ("brittler") than ceramic thus I suppose stiffer floor needed.
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Unread 11-14-2003, 04:56 PM   #15
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Putting the beam 8 feet from the foundation wall is fine. Make sure all the joists in the tiled area is supported on the beam.

Sistering the joists after the beam (or with the beam) will make your floor stiffer, but the beam makes this un-necessary. So save your energy for hauling CBU and Mud. You're gonna need it.

The previous floor was a mud bed. That technique solves a lot of problems and is the best you can get, if you or someone you know can do it for you. Also, ceramic tile is more forgiving as far as subfloor is concerned. This is because, as you guessed, the natural stones are more brittle (some of them anyway) and have natural defects in them. They require a stiffer floor than ceramic tile.
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