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Hello again,

I have been thinking about this a lot as I'm about to start replacing the floor in my bathroom.

As things stand now, removing the old flooring (1/4 inch plywood over about 1 inch of subfloor) I have found that there is actually an old floor from the late 1800's underneath all of that, with some rotting joists built on top of it. All of the joists are going to come out and be replaced. This is leading me to slightly panic as I am not sure how much room I need to leave to have my floor (subflooring, cement backer board and 12x12 tiles) be level with the adjacent rooms.

As I am installing new joists across the bathroom floor, I have to know how far below the adjacent rooms floor I should place the tops of them. I do believe 12 x 12 tiles are 3/8 of an inch thick, the backer board is 1/4 inch, and the subfloor, 1/2 inch? 3/4 inch? Or do I need more subfloor than that?

I am assuming the mortar will add some height as well?

Looking for any advice. Rest of the old flooring / joists is being removed tomorrow and would like to start replacing it this weekend.

Thanks!
 

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Tileguy
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6,050 Posts
Hi Jax,

I am not understanding what this means.

Jax said:
..........there is actually an old floor from the late 1800's underneath all of that, with some rotting joists built on top of it.
First remember that joists can vary ⅛" from their industry specs. 2x10's should be 1.5 x 9.25" - 2x8's 1.5 x 7.25".

You need ¾" subfloor grade ply or an OSB subfloor such as Advantech. Ply usually measures 1/32" thinner than its stated thickness, but the construction adhesive on the joists may take care of that.

The CBU may be a true ¼", add 1/16" for cured thinset under it though. The tiles are not manufactured according to SAE specs, (inches or fractions thereof), but yes close ⅜" for most. Add 3/32" for thinset. And there you are........ Have the materials on hand to double check, but if you're within 1/16", you can tweak a bit while setting the tiles.

Remember you'll need in install some kind of molding or threshold in the doorway so it doesn't have to be exact.

Jaz
 

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This is no bull.....
I seen walls layered..
Plastered, then leveled , paint.
Over that drywall, then paint, wall paper, paint.
Over that more drywall, paint etc....

Then dealing with 3-4 layers of floor and I mean systems, siding, etc..........
 
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