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Unread 08-13-2021, 10:15 AM   #1
chrishmm69
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Chris's Kitchen Tile Project

About to embark on our kitchen remodel, started with the Deflecto calculator to find out our current joist setup is slightly deficient.

Good condition Doug Fir, 2x8 (7.25" actual), 11.5' unsupported. Yields an L/337. A bit short of 360.

However, I believe the subfloor is pretty wavy/out of level, so I was planning on sistering joists anyway to help even it out. Deflecto calc says I can get away with adding just a 2x4 sister (it will add an additional L/45...plenty)

The problem is...has anyone ever seen a 12' 2x4 that was not in pretzel form?

So my question is - can you use something like a tie plate, etc from Simpson Strongtie to tie together two shorter length 2x4s into one long one, and still have it work for adding "L"?

Thanks in advance.

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Unread 08-13-2021, 11:54 AM   #2
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Welcome back, Chris.

I wouldn't try using 2x4s to flatten the joist tops just because of the difficulty of proper fastening. I would always use at least 2x6 material and yes, you should be able to find those in sufficiently good condition for your needs.
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can you use something like a tie plate, etc from Simpson Strongtie to tie together two shorter length 2x4s into one long one, and still have it work for adding "L"?
No, you cannot use two boards spliced together when sistering to reduce deflection. And you certainly do not want to increase your "L" value. If you could actually reduce the length of your unsupported span, you'd not need the sistering at all.

My opinion; worth price charged.
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Unread 08-13-2021, 12:43 PM   #3
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Thanks! Its been a long while since my last project.

Will go with 2x6's then.....even if I have to have a lumber yard deliver them.

I can technically reduce the space by half a foot fairly easily, but I still assumed I would need to sister the joists anyway to bring them all into level.

Ive done the sistering to bring into level before, but only in a small room (5'x10') so amount and quality of lumber was easy to guarantee.

Is there a better way to do it in a larger area? My kitchen is 12'x18'.

Thanks again.
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Unread 08-13-2021, 02:39 PM   #4
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A possible fix for the deflection - our foundation walls (which support one end of the kitchen joists) are 6" thick concrete. The sill plates for the exterior walls (where the kitchen joists land on top of) are double 2x4s. Which leaves a double 2x4 size gap between the joist and the inner half of the foundation wall. If I add another set of double 2x4s under the joists along with some flat material to make sure the blocks contact the joists, I reduce my span by 3.5" (the width of a 2x4 laid flat, of course) and Deflecto gives me the thumbs up.

Does that sound acceptable? I mean I know it gives me the thumbs up, but is the difference between "good to go" and not, simply that 3.5 inches?

And since its in regards to the unsupported span of each joist, can I use a double 2x4 block between each joist and the top of the foundation wall? Instead of having to finagle 18 linear feet of double 2x4 in there.
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Unread 08-13-2021, 05:40 PM   #5
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'Fraid I can't follow your description, Chris. Suffice to say the calculation is based upon the unsupported span of your joists. If you want to do your calculations down to the inch, that's entirely up to you.

But if you are planning to sister the tops of your joists for the purpose of flattening or/and leveling, it shouldn't matter much in your particular case if you reduce your span by 3 1/2 inches, right?

My opinion; worth price charged.
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Unread 08-13-2021, 06:08 PM   #6
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I was calculating down to the inch because it does seem to make a difference.

Ive used other calculators that say my setup is good the way it is, I know Deflecto is more conservative. No issue with that, but 12 foot long boards would be hard to install in some spots just because of the location of the joists vs other obstacles in the basement (ductwork, mostly).

If I was able to "officially" get the deflection correct, I would be able to piece the sistered joists together in spots that I couldnt get them in place as one single board.
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Unread 08-13-2021, 06:24 PM   #7
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I can find you a number of joist deflection calculators that will say your joist structure (absent all the defects, of course, and based upon new material) meets building code (L/360) and that is, technically, the ceramic tile industry requirement for tiling a floor.

It's entirely up to you what you're willing to tile over. If you like it, I like it. See my warranty information below.

My opinion; worth price charged.
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Unread 08-13-2021, 09:45 PM   #8
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lol i hear ya.

The area has been tiled for a very long time and we never had issues with grout or tile cracking. But I tend not to trust what was already in place. After pulling up the cabinets today, we were greeted with a somewhat decent subfloor, followed by a hodge-podge of plywood on top of it, then a layer of old linoleum, then the tile floor we're used to.

I kinda wonder if the linoleum provided enough "cushion" to keep the tiles and/or grout from cracking all of these years. Or maybe the deflection is just close enough to not cause an issue.
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Unread 08-13-2021, 10:56 PM   #9
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Chris, it is more common for the tile surface to fail from a deficiency in the between-joist subflooring deflection than from the joist deflection, but you really want both to meet the industry standards. For the subfloor you want to exceed the industry standard by a good bit if you can.

My opinion; worth price charged.
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Unread 08-19-2021, 11:12 AM   #10
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Thanks, CX!

Im about to start sistering the joists. 12' long 2x6s from a lumber yard...."straight enough" for my uses.

The existing subfloor is gone. Years of water damage (before we owned the house) yielded some...."interesting"....fixes from previous owners. Stack of linoleum tiles, old school wood panelling, etc....all UNDER the tile floor. No wonder why our nice new fridge was almost impossible to level.

Another question - Advantech says not to land the T&G joint on a joist (for good reason). If the boards come together in between joists, do I need to add blocking between those joists, so I can support the joint? Or was a suggestion I thought I saw here the correct one: strips of plywood "straddling" the board joints, glued and screwed directly to the underside of the Advantech.

Thanks in advance.

-Chris
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Unread 08-19-2021, 11:45 AM   #11
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Quote:
Originally Posted by Chris
Advantech says not to land the T&G joint on a joist
I'd like to see a link to that information, Chris. Not computing for me.
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Unread 08-19-2021, 01:01 PM   #12
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Well, of course I cant find it now! Their installation manual doesnt mention not to, and in fact most of their images actually show the joint landing on a joist. When I used it in my bathrooms, the joint would end up a slight high spot in the floor, I figured because I was landing it on a joist. It was easy enough to sand down (wasnt high by much) but I was thinking maybe it wasnt supposed to be that way.

So I guess that solves that question. But their manual does not show or note what happens if a joint between two boards ends up "floating" between joists (i.e. non-standard spacing, like I have in a couple spots). Of the 16 joist cavities, 12 or 13 of them are 16" OC so the boards "should" land OK. But the other 3 or 4 are not 16" OC. One is 19" but Im going to add hangers and joist in between, so it will become about 9.5". And one right next to it is small, probably about 5" OC. For now I will hold off on adding the joist and hangers, maybe a board will land somewhere in between and thats where Ill put a new joist.
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Unread 08-19-2021, 01:05 PM   #13
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If there no more joists to be added, just cut the plywood so that the short edge falls halfway across the joist, i.e. 3/4" on a nominal 2x.
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Unread 08-23-2021, 12:14 PM   #14
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Making progress.

When the pulled the subfloor up, it looked like the previous installers had stock in a nail manufacturer. So many nails, and a lot of them ring shank.

Unfortunately removing them took their toll on one of the joists (see attachment)


Ideas to fix it? I came up with two:

cut out the "chunked" portion, cut a corresponding patch from new joist, glue and nail/screw it in place on the existing.

or....a whole new full size joist, glued and bolted to the existing. This is a little tougher, because it will be hard to maneuver the full piece in place (obstacles, ceiling, etc). Really needs to be 14' long for full support (to match what is already there), and since its the same 2x8 as existing Im guessing it will need a lot of persuading with a sledge hammer to get into place.

What does everyone think? (also whatever solution I use, I will be sistering a 2x6 onto it anyway because the originals are not level)

Thanks.
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Unread 08-23-2021, 02:24 PM   #15
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I'd sister it as much of the length as you can. As long as the ends aren't damaged, you don't necessarily have to have the new joists at full length.

Use a good amount of construction adhesive and 3" deck screws. Sister both sides if you want.
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