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Discussion Starter · #1 ·
Greetings,

I knocked out my old 70 year old tile floor in my upstairs bathroom yesterday(above kitchen). The demo went smooth, but now I'm left with an old subfloor with old, 1-inch thick wood planks nailed to the floor rafters that is about 5 inches lower than the hallway floor.

I want to put new tile down, but I'm unsure what to do about the height difference.

Should I pull up the old wood planks, and just put like 3 inches of plywood down, then 1.25 inch cement backer board, and then the tile and hope it is level with the hallway floor?

Any suggestions would be welcome!
 

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If it were me I would pull up the old subfloor and sister a 2x on the current joists to bring the joist up to the right height so when you add your plywood and backer board and tile it will be the same height as the hall.

I would think 3 inches of ply would be pretty heavy and costly. If you bring the joist height up and then lay down 3/4" ply and then another layer of ply at least 1/2" thick and then thinset and your backer it would be better than all that ply. I've read that you should have at least 1.25" of ply and then backer for tile.
 

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Discussion Starter · #3 ·
Excuse my ignorance, but when you say sister, do you mean take another 2x8 and cut it to the length of the bathroom, and then nail it in place to the existing joists, but 2 or 3 inches higher?

If so, how would I be able to ensure that the sister joists are level enough to lay the plywood on top?

Thanks!
 

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Yes that is sistering. You can figure out at what height you will want your joist to sit at. Draw a level line across the wall at one end of your joists so all the joist are level. Then attach the joist on that side at the line and then use a level to make sure the joist is level and nail the other end of the joist. Then everything should be level.

Another option if your current joist are level you can cut 2x material so it sits on top of your current joists. I have seen where people of done this and then cut a peice of 1/2" plywood and nailed it on each side of the joists to secure the new joist on top of the existing joist.

Hope this makes sense and hopefully someone can give some more details. Good luck
 

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Discussion Starter · #5 ·
what about just dumping concrete over the old subfloor, and then laying the tile on top of that?
 

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I'm not familiar with concrete and how that would go. I do know that some tile guys will lay a thick(3-4") mudd pan for tile. I have no experience with that either. For me it would be easier to build the floor up like mentioned above. Guess it depends on your skills if you want to build the joists up or go the concrete route. Hopefully someone else will join in with more experience.
 

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I'd figure the tile height, thinset, 1/2" cbu, thinset, 1/2" ply, break diff. joint (not CDX), 3/4"ply, glue, ripped 2x's to tops of joists over 1x? planks, glue. Tile height to match other room's floors. Wait for a tiler to chime in. Be safe, GBAR
 

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Discussion Starter · #8 ·
Hi,

After I add sister joists, you are saying I should add:

3/4" ply
then break diff. joint(what is that?)
then 1/2" ply
then 1/2" concrete backer underlayment?
then the tile?

Thanks!
 

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Discussion Starter · #10 ·
GBAR -what exactly did you do a search for? When i clicked the link, I got this:
Sorry - no matches. Please try some different terms.

Thanks
 

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Be careful if you decide to add 3 or 4 inches of concrete. Concrete has a unit weight of about 150 pounds per cubic foot. A 3 inch thick layer of concrete will add about 37 pounds per square foot (psf) to your floor load, a 4 inch thick slab would add 50 psf to your floor load.

Floors are typically designed for a total of 40 psf dead load, plus live load which varies with the room (and the building code). By adding so much dead weight, you could exceed the design capacity of the framing for the bathroom. This could result in excess floor sag, cracking of the joists, or even collapse in a worst case scenario.

The suggestion about adding a 3 inch board onto the top of each joist seems to have a lot of merit. You are not looking for extra bending strength, so you can attach it by nailing, screwing or gluing to the existing joists, then use standard plywood and backer board above it. It will add virtually no weight to the floor. And it will not require potentially awkward sistering of a new joist onto the old one.
 
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