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Old 05-30-2003, 09:49 AM   #1
Brewbeer
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Floor Tile / Deflecto Question

Hey folks, got some questions regarding the structure of my kitchen floor, and if I can put 13 x 13 tiles on it.

The kitchen has two sections, one section is 8 feet between supports, 2x8s (7.5 x 1.5) of unknown kinda knotty floor joists 16 inches on center. Deflecto sez this section is ok for ceramic tile.

The other section is 11 feet between supports, same 2x8s of unknown kinda knotty joists 16 in on-center, with 2x6s sistered to them.

The entire floor is two layers of plywood totaling 1 1/8 inch, overlain by the original 1957 linoeum, with a second layer of vinyl stick-on squares added about 25 years ago.

My plan is to rip off the two layer of vinyl, and 1/4 inch cbu and tile. Am I good to go or do I need to beef those joists up?

Thankx guys.

p.s., the shower is awesome, thanks so much for helping me through that project. Wife loves it and won't use the shower/tub combo upstairs anymore. Everone who looks at it drools. The town building inspector was impressed. Thankx again.
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Old 05-30-2003, 11:28 AM   #2
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Your longest joists are about L/430, which is fine for most ceramic tile. However, I think for large format tiles, you want to treat them like natural stone, which has a deflecton limit of L/720. Getting to L/720 will require another 2x8 sister. If there was a way to reduce the span, there would be no problem. On the other hand, if you went with a 10x10 or smaller tile, then your floor is fine.


A beam placed somewhere near the middle of the span will solve the problem. Let me know what you want to do, and I'll help.
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Old 05-30-2003, 12:33 PM   #3
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Thankx bb.

So the 2x8s sistered to the 2x6s over 11 feet give me a deflection of L/430?

The overall kitchen is about 20 feet long by 11 feet wide. The joists run width-wise. There is a staircase down to the basement, so for about the first 10-12 feet, the joists are 8 feet long. Deflecto gives me L/481 for these. In this part of the kitchen, there are counters on either side, so only the middle 4 feet or so gets any "live" loading.

The remaining section of the kitchen is a little more complex. Starting where the 8 foot long joists leave off, the first 11-foot unsupported joists is a double 2x8, which carries the beam that supports the shorter joists, then a 18 inch wide bay to a 2x8 sistered to a 2x6, then a 13 inch bay to another 2x8/2x6 sister, then a 13 inch bay to another 2x8/2x6 sister which has under it a wall running parallel to the joists, followed by 3 more 13 inch bays with 2x8/2x6 sisters, to the wall above (supported by a double 2x8), but the last 3 are only 8 feet long unsupported, as there is a wall 3 feet out from the center beam (the wall to the new basement bathroom). The walls under this part of the kitchen are solid; I used a sledgehammer to get the cut-slightly-too-long wall studs forced between the bottom plates (resting on concrete) and the top plate (screwed to kitchen floor joists above).

An additional supporting beam is not really an option due to the laundry area being under the kitchen. Additional sisters might not be an option either, as when I put the bathroom in, I moved the water supply pipes and wiring up into the joist bays through drilled holes.

So, my best large-format option here is a 10 inch tile? Can I still lay these on the diagonal relative to the orientation of the joists?

Thankx again.
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Old 05-30-2003, 02:32 PM   #4
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Starting where the 8 foot long joists leave off, the first 11-foot unsupported joists is a double 2x8, which carries the beam that supports the shorter joists, This concerns me, because, in addtion to the distributed floor load, it also carries 1/4 of the 80+ square feet at the stairs. Unless the stair well framing is supporting some of the beam that supports the shorter joists, or the doubled 2x8, the deflection of the doubled 2x8 will exceed L/360. You sure you can't sneak a post in there somewhere?


You do have 1-1/8 plywood subfloor. That's a real plus in your favor. It's the between-joist deflection that kills the larger tiles.

Do you have bridging between the joists? This will allow the joists to share the load, so a single joist will not deflect much more than its neighbors. It can be added if necessary.

I'd like John to look at the size tile you're considering. I may be off base about that. (wouldn't be the first time...)


Bob
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Old 06-02-2003, 08:00 AM   #5
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bb, it will be possible to put a post where the double 2x8s and the stairwell beam intersect. The post would land at one corner of the base of the stairwell. Also, eventually there will be a framed wall under most of the beam. Right now there are just two 2x4 between the beam and the concrete floor, one at the double joist/beam junction, the other roughly ½ way between the ends of the beam. If I constructed a framed wall 6 feet long beneath this beam, would this get me where I want to be? Would 2x4s 12 inches on center with a triple 2x4 at the post location, resting on a pressure treated 2x4 on the concrete flooring be sufficient for this purpose?

As far as joist-to-joist bracing, there is old-style wooden cross bracing original to the construction of the house in 1957. The cross-bracing has been removed in one of the 8-foot bays to accommodate a natural gas line, and the cross bracing between the 2x8/2x6 sisters has also been removed. The installation of additional cross-bracing is possible. What do you recommend for additional cross bracing? Sections of 2x8s?

Would pitchers help?

Thankx, --=--Ed.
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Old 06-02-2003, 08:12 AM   #6
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Keep it up Ed, yer gonna make Journeyman yet
Looks like Bobs got you handled.I just did a floor with a similar situation as yours. I built a beam.1 2x8 sandwiched with plywood and 2 basement jacks.1 beam fell in an area that would be seen .At the big box,they have a nice column cover that just folds around it .Paint it and its a done deal.
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Old 06-02-2003, 10:50 AM   #7
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Your bearing wall sounds good, I'd only add a second top plate (in case the joists don't fall directly over a 2x4), and I'd do this before tiling. If you wait you may disturb the tiles when you squeeze that wall into place.


Hey, Todd! The orginal question was about 13x13 tiles. I'm under the impression that large format tiles should be treated like stone (double wood subfloor, L/720, etc.). What do you think?
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Old 06-02-2003, 10:58 AM   #8
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I would construct the bearing wall directly beneath the beam that carries the shorter floor joists, and put the triple 2x4 post at the end of the beam, where it meets the double 2x8 joist (which is 11 feetlong, unsupported). So, I'm assuming that I would not need a top plate, as the studs would be directly below and nailed to this beam.

Is the 2x8 blocking between the joists something I should do? Any suggestions as to spacing?

Thankx guys.
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Old 06-02-2003, 11:15 AM   #9
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That will work, too. However, you may find it easier to make up a wall panel on the floor and raise it into place, rather than toe-nailing the studs to the beam. In this case, use a single top plate.

As to the blocking, (sorry, I didn't address it before). At this point, it is easier to slip in short pieces of 2x and either toe-nail or thru-nail them in, you can also use screws. I usually advise 2 rows of blocking at 1/3 span, but a single row at midspan is almost as good. They don't have to align perfectly, but it helps if they were lined up, since you are making another beam thru the floor. Where you have a 2x6 sister, just use 2x6's. Notching the 2x8's would be a real pain, for very little gain. If you have a bay with a duct or something, it won't hurt to leave the blocking out, as long as the adjacent bays are blocked.

Got a pneumatic nailer?
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Old 06-02-2003, 12:07 PM   #10
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Thankx bb.

I don't have a nailer, but I do have an impact drill and will be using screws through pre-drilled holes. Much easier than nailing by hand especially into rock-hard 45 year old joists.

So, if I put in the bearing wall, and blocking as described, am I good-to-go with the larger format tiles, or do I need additional sister or a smaller format tile? Thankx again.
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Old 06-02-2003, 12:48 PM   #11
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I'm still waiting for one of the pros to comment on the requirements for large format tiles. I think you are supposed to treat them like natural stone, which requires double wood subfloors and L/720 deflection. Your subfloor is double wood, but your joists are L/430-ish.
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Old 06-02-2003, 05:17 PM   #12
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Hi Bob,

The 13x13 tile would not be considered a large format ceramic. Over 16x16 for that.

My thoughts are that adding the beam and the double plywood would make for a very nice floor. The addition of the 1/4" cement board properly applied will be just fine.

L/480 is what I get but I ain't no inguneer either.

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Old 06-03-2003, 10:02 AM   #13
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Great!

13x13 it is!

Bob
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Old 06-03-2003, 12:17 PM   #14
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Thumbs up

Thankx guys.

Looks like I got a good plan.,
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Old 06-03-2003, 12:50 PM   #15
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Bob, I would have to go along with 16x16+ being large format tile.However,it never hurts to consider the rooms use.With any ceramic L/360 is minimum.and minimums do not take into consideration large family gatherings of italians with every aunt hanging in the kitchen making sure the sauce is just so.
There is also the church ladies gathered making pies for the bake sale,and uncle joes bowling team.
My point is minimum is minimum.I like maximum better,and seeing as we dont know what maximum is,build it bigger better stronger,just to be safe
We dont need a 6,000,000.00 Bionic floor,but something over a buck and a quarter helps
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