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So I have a 1945 house with a bathroom that has a sloping floor. It is out of level 7/8". I have taken the floor down to the original plank subfloor which is 3/4" thick and perpendicular to joists. I am planning on using Ditra and installing Ceramic hex tile 9x9".

I originally had planned to use self leveler to level the bathroom as it is only 5 x 6.5 feet. But with a total slope of 7/8" this isn't feasible and will also lift my floor too high above the bathroom threshold.

So I have tried to research as much as I can and can think of 3 possible solutions but am looking for thoughts as I am new to this.

Option 1: I keep the original 3/4" subfloor planks and attach 15/32 plywood over top with screws (Ditra manual recommended subfloor). Then level just my shower base area as I can just have the slope drop taken in by my shower curb (so shower curb will drop a bit more outside the shower). For the remaining area of floor outside my shower pan I will use self leveler again. From the shower pan edge to the door threshold my slope is 5/8". I am worried that this may still go above my bathroom threshold but its already janky so ...

Option 2: I remove old plank subfloor, sister joists below with 2x4 on either side and level the bathroom from below. Then place new plywood on top. Not sure on the thickness of this. Ditra manual says 19/32 but that seems so thin to me! my concern with this option is blocking for the new plywood around perimeter. I am also scared to remove old subflooring. Is this okay? will it weaken house at all? I have a circular saw but obviously it wont go right to the edge, so how do I deal with that bit of subfloor I cant cut out?

Option 3: I use the 15/32" recommended ply over the flooring outside the shower pan with Ditra, and I use 1/4" ply under just shower pan. I use self leveler over the entire bathroom or do the pan and then the outside floor. The 2 plywood thicknesses will help alleviate the slope a bit so not so much self leveler is needed.

I already ruled out using shims between old plank subfloor and new plywood to level because the floor thickness will lift high above the bathroom threshold that leads to a wood floor hallway. Bathroom threshold is currently a marble piece and is 2 -3/8" from joist to top.

Hope this is making sense. I appreciate any help on this. Thanks! enter image description here

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Sarah
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  • If the slope is flat and does not bother you, then levelling not required. Hard type floors like tiles only require the floor to be flat, not level. If the floor rises and dips that does need fixing. – crip659 Aug 26 '23 at 20:35
  • I do need to level the shower pan section for drainage in my pre-sloped pan, but I did wonder if I could get away with the floor area just being flat and not level. Any recommendations for if there are humps and valleys and how to correct if I cant use self leveller? – Sarah Aug 26 '23 at 20:43
  • Humps and valleys do need to be levelled/flatten. The cause of them will help with the fix, depending on how far you want to go. Quite often the joists are the problem with being not level with each other, so shims might be needed. – crip659 Aug 26 '23 at 20:52
  • A remote possibility is the house settling at one end. In which case there could be a different solution. – Rohit Gupta Aug 26 '23 at 21:46
  • Honestly, out of level isn't a problem as long as it's *flat* out of level. If it *really* bugs you, why not use 1/4" floor underlay ply and basically make a large (stacked) wedge? You can use leveler to make it flat, or simply use the thinset to do that when you put the Ditra down. – Huesmann Aug 27 '23 at 12:35
  • Good point on the replies stating it doesn't need to be level but only flat. I think I am going to just level the shower pan area and then see what I have left to work with. Either level the outside area too if it wont rise above threshold, or just make sure the surface is flat for Ditra and tile. – Sarah Aug 27 '23 at 14:02

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