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Old 08-04-2018, 06:41 PM   #1
Rurak
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Kitchen remodel

Hello everyone. As the title implies we are remodeling our kitchen. Here are the details on existing conditions. 2x8 floor joists 16 oc. 12 foot span. Sub floor is 3/4 barn boards with about a 1/4" gap between them. The previous owner removed hardwood, installed 1/2" cbu over existing subfloor and then placed cabinets and island on top of tile. As you can imagine we have quite a bounce in the middle of the floor, so much so that we are losing grout and cracking tiles. I have begun sistering the joists with 7 1/4" LVLs glued to subfloor and existing joists, 3 10d nails every 16 inches and will run 3 rows of solid blocking in each bay. I do not want to remove the island or cabinets. My questions are these:

Will I meet the deflection requirements with the sistered LVLs for ceramic tile? (wife wants 36" x 6" wood plank)

What are my options for 1/2" substrate? I don't want to raise the tile any higher than it already is.

Any other suggestions are greatly appreciated. Thank you.
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Old 08-04-2018, 07:47 PM   #2
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Welcome, Thad.

Your joist structure was just a part of your problems.

Installing the CBU over sawn board subflooring with big gaps between boards was borderline suicidal for a ceramic tile floor. If you repeat that you can expect more tile failure.

The absolute minimum you can do with such a subfloor is install nominal 1/2" exterior glue plywood with no face of grade lower than C and then your tiling substrate of choice. And that method is predicated upon your subflooring boards being T&G style and oriented perpendicular to your joists.

Sistering with LVLs will most likely give you a sufficient joist structure assuming the added joists are at least 1 1/2" thick and you've sistered a minimum of the center two-thirds of the unsupported length of the original joists.

The between joist blocking is not gonna buy you anything and I'd recommend you save yourself the time and trouble of adding them.

My opinion; worth price charged.
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Old 08-05-2018, 07:43 AM   #3
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I've sisterd the entire length ensuring a minimum of 4" of the LVLs are on the bearing points (one end being the sill plate on top of the foundation wall, the other on top of a center carrying beam). Would you recommend removing the existing subfloor amd installing 3/4 t&g plywood? I don't want to do that but I can if I have to. If I choose not to and add 1/2" plywood what is the minimum thickness of substrate you would recommend?
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Old 08-05-2018, 08:33 AM   #4
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It's not at all necessary to have the sister joists supported at the ends, but it doesn't hurt to do that.

Removing and replacing the board subflooring is a good idea if your existing subflooring is in very poor condition or if finished floor height is a serious concern. You'd want to start your new subfloor with at least nominal 3/4" exterior glue plywood or OSB.

And it would have been much more effectively done before you did your sistering so you could bring your joist tops into plane and level them if desired.
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Originally Posted by Thad
If I choose not to and add 1/2" plywood
If you keep the board subfloor, you don't have a choice. No manufacturer of tiling substrates will allow you to install them over your sawn boards. You've already seen why.

You can chose tiling substrates that are less than 1/16th" thick up to those that are 1/2" thick or greater.


My opinion; worth price charged.
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Old 08-05-2018, 02:10 PM   #5
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Since tiling over 1/2" plywood with my,existing subfloor is not an option what substrate is 1/16" thick? I really don't want to raise my finished height.
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Old 10-11-2018, 03:40 PM   #6
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Tile in my kitchen

Hey everyone. As the title suggests we are going to be tiling our kitchen. I removed the existing tile and backerboard. The joists are 2x8 16" o.c. I sistered each joist with 7.25" LVLs. Glued and nailed to the existing joists. I also installed 3 rows of solid, full depth blocking, ome in the center and one ris 3 feet each side of center. Sub floor is 3/4 pine boards. I nailed those off to the new joists with 8d ring nails. Can anyone calculate my deflection? I'm trying to get away with a 3/8" substrate to avoid transitions to existing floors and I'm having a hard time calculating it one the website because there is no option for sistered or engineered lumber. Thank you.
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Old 10-11-2018, 03:49 PM   #7
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I forgot to mention a few things. The tile we chose is 6x36 wood plank. I was planning on using flexbond mortar and epoxy grout, the lower cabinets sit on top of the old tile so I renove tile and cement board up to the toe kicks and around the island.
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Old 10-11-2018, 03:55 PM   #8
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I do not know the answer, but I know the first question... what is the span?

I believe that the LVLs are significantly stouter than dimensional lumber, so if you sistered the full length you could consider the joists to be double thick, and use the deflecto.

As far as the subflooring, I think the right answer would have been to remove the boards, and put down 3/4" T&G plywood. The experts will chime in, but I don't think anyone is going to like boards with only 3/8" of something over them. We shall see!
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Old 10-11-2018, 04:04 PM   #9
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The span is 12 feet. LVLs are 7.25x1.75. I'm sure I would have been better off with 3/4 t&g but hindsight is 20/20
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Old 10-11-2018, 05:31 PM   #10
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How are the pine boards oriented to the joists, perpendicular or diagonally?

The bare minimum thickness of plywood would be 1/2".

You may want to bump that up to 5/8" ply if the boards are installed diagonally.
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Old 10-11-2018, 05:47 PM   #11
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Thad, it'll help if you'll keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered.

You can see our advice hasn't changed from your first thread, eh?
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Old 10-11-2018, 05:51 PM   #12
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Thad, it'll help if you'll keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered.

You can see our advice hasn't changed from your first thread, eh?

Your joist structure should now be fine. Your subfloor is still not.

My opinion; worth price charged.
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Old 10-11-2018, 06:11 PM   #13
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Sorry for the double post. I couldn't find my original post and couldn't remember the outcome. If I use 1/2" plywood I will have a height issue matching existing floor. 3/8 plywood will match the hardwood perfectly but I can see from everyone advice that 3/8 plywood is not sufficient. This has been a very frustrating remodel. Do I habe any other options? My wife is due with our second child any day and i would like to avoid laying tile with a newborn!
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Old 10-11-2018, 07:20 PM   #14
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Only other option would be to remove the existing board subfloor and replace it with a first layer of nominal 3/4" plywood. Then additional plywood if you desire and the tiling substrate of your choice.

Best bet if your existing subflooring is in good condition would be to install the required plywood, substrate, and tile. Make your floor suitable for the tile installation, then make your transitions to adjacent flooring as necessary.

Transitioning to hardwood flooring is one of the easiest transitions to make.

My opinion; worth price charged.
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