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I am putting new tile in bathroom which has 1x6 planks diagonally across joists. I need to raise this floor 1 3/4" to match the toilet flange, door jambs etc.

What’s the best way?

Currently I am thinking to double up 1 1/8 ply (in strips to save on cost) with 3/4 T&G ply on top.

What’s the best way to screw all this on top the existing planks? First layer to joists second not? Both to joists? Both not?

Having all these layers worries me but i need the height.

I am putting ditra + tile on top of this stack....

subfloor

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  • I do not know where the 1 1/8" figure comes from. "double up 1 1/8 ply" That is 2 1/4" no? Take the thickness of your tile/thinset/ditra and subtract it from the amount you need to raise in order to meet the flange/jambs, that is amount of sub-floor you need. – Alaska Man Apr 6 at 17:38
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Given the amount you want to raise the floor I'd suggest 2x1" planks screwed to each joist (+0.75") with the 3/4" on top of that (+0.75"). You should then put a sheet of 1/4" ply on top. This way if you ever need to remove the tiles / ditra you only need to tear up the 1/4" ply and can leave the 3/4" floor intact.

Also, make sure you stagger the plywood joints.

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  • Thanks Joanathan! Should the 3/4 and 1/4 both screw into the joists as well? Just the 3/4? Neither? – Yuri Apr 6 at 16:06
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You should aim for two layers of continuous below the ditra, 3/4+1/2" for the best chance at controlling movement, the top 1/2" should only be screwed into the layer below without penetrating the joist. If you need to add some additional height you can use Ditra XL as well.

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