I understand the minimum bathroom subfloor thickness of 1 1/8". I currently have 1 1/16" and want to install hardibacker but need to minimize the height increase at the door threshold as I install new tile. Can I replace the top plywood layer of the subfloor with hardibacker or similar products to achieve the minimum thickness? In other words, does hardibacker count as part of the subfloor thickness or must that be added in addition to the subfloor?

Hi,

Hi,

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I understand the minimum bathroom subfloor thickness of 1 1/8"

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That is not true. You can safely install Hardie and then ceramic tiles over 3/4" ply or OSB when the joists are 16" and 19.2" o.c. Actually Hardie says 5/8" is all that's necessary. That scares me, so I say 3/4".

The double ply requirement is for natural stone tiles. You still have to install a concrete backer or membrane of course.

Hardie nor any other CBU add structural strength to the system. They do not count as part of the subfloor. All they do is provide a tile-friendly surface to tile to.

Jaz

This you would have to check with your local building dept. Every town/city have their own requirements. Some areas are less strict then others.

Chuck

Hardibacker could toward your sub floor thickness if you glue and screw it. You must glue it with thinset or a material which works with your existing subfloor material. Screwing every 6" in all directions is also needed, no cutting corners with the screws or the thinset.