I'm taking up hardwood floor in a bathroom and will be replacing with tile. The hardwood was put in over wood chipboard(?) subfloor with 1/8" plywood underlayment. In order not to have a huge height disparity between the wood floor l'm leaving and the new tile, can install a new 1/8 underlayment under the Ditra plan to put under the tile?

Pictured is the tile on top of the existing underlayment up against the wood floor that will remain. tile on top of underlayment

  • 1
    The thickness of the sub floor is important to know. Tile likes a very solid(inch plus) floor. Tile does not bend, so if the floor moves under weight it will usually crack. Extra wood to raise it up is okay.
    – crip659
    Oct 7, 2023 at 18:03
  • @crip659 how do I check that depth? Home built in 2001 so I would guess it should be thick enough? Doesn't seem to flex under weight and it's only a 5ft x 5ft space.
    – TheGremlyn
    Oct 7, 2023 at 18:05
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    The easy way is just drill a hole though it. Most sub floors are only 3/4 inch or even 1/2 inch if saving money. Most tiles are quite fragile. They should come with installation instructions on what is needed.
    – crip659
    Oct 7, 2023 at 18:12
  • Why the Ditra? Are you looking for a waterproof layer to protect the subfloor?
    – popham
    Oct 7, 2023 at 19:43
  • Planning to use it based on recommendations, but not specifically for water proofing. Only a half bath.
    – TheGremlyn
    Oct 7, 2023 at 19:48

1 Answer 1


According to Schluter's Ditra Installation Handbook (linked from the downloads section of https://www.schluter.com/schluter-us/en_US/Membranes/Uncoupling-(DITRA)/Schluter%C2%AE-DITRA-&-DITRA-XL/p/DITRA), a Ditra underlayment needs minimum thickness of 3/8":

Place underlayment panels (Exposure 1, plugged-face plywood or OSB of minimum 3/8" (10 mm) thickness) with long dimension perpendicular to floor joists....

The handbook goes on to provide precise details for fastening, gaps between sheets, and other minutiae. You should definitely take a look at the whole page worth of information.

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