Subfloor Requirements Before You TIle

One of the most important considerations for tiling a floor is ensuring that your subfloor is strong and ready to tile. Tile cannot flex like vinyl or carpet, so if your subfloor is not rigid enough, you have potential for broken or popped tiles. After all of your hard work, this is the last thing you want!

There are several ways to reinforce your flooring to prepare it for tile, and here are three of them.

OptioN 1: Total Height 1 1/4" + Tile Thickness

Depending on your space, the easiest option may be to add a sheet of plywood over top of your OSB subfloor. This option uses a 5/8" thick plywood over top of 5/8" OSB subfloor. Make sure to glue and screw this subfloor for extra rigidity and durability. Use standard plywood, NOT "good one side" plywood for a tile substrate, as it is hard for the thinset to adhere to it, and your installation may fail. 
Keep the plywood indoors 7-10 days prior to installation, so it can acclimate. When sheeting, leave a ¼” gap between sheets and fill it with thinset.
Screws are only to be the combined thickness of your subfloor + your base to which you are fastening to. You do not want to screw into joists. 
When sheeting an area that will be exposed to moisture it is better to use an uncoupling mat (see Option 3).​

Option 2: Total Height 1 1/4" + Tile Thickness

This option is almost the same as Option 1, except that if your subfloor is thicker, you can use a thinner sheet of plywood over the top: 1/2" plywood over 3/4" OSB subfloor. Don't go less than 1/2" plywood for a tiled floor, otherwise it may warp. Glue this subfloor for rigidity and durability. Use standard plywood, NOT "good one side" plywood for a tile substrate, as it is hard for the thinset to adhere to it, and your installation may fail. 
Keep the plywood indoors 7-10 days prior to installation, so it can acclimate. When sheeting, leave a ¼” gap between sheets and fill it with thinset.
When sheeting an area that will be exposed to moisture it is better to use an uncoupling mat (see Option 3).

Option 3: Total Height 3/4" + Tile Thickness

If you are limited in height (eg. accounting for a threshold or other fixed elements such as cabinets) the thinnest option is using an uncoupling membrane. Also, if the area you are tiling may be exposed to moisture, such as a bathroom or entryway floor, an uncoupling membrane is a more stable substrate than plywood. Plywood expands when it gets wet, and can compromise your installation. 
Übermat or Schluter Ditra are two brands available in 1/8" thick mat, resulting in only 3/4" thick overall height. The requirements for Übermat/ Ditra are joists that are max 16" on centre, and 5/8" thick OSB subfloor.
Tiles are installed over Übermat with thinset, and the shape of the mat creates "pillars" of thinset mortar which are incredibly strong, durable and resistant to movement. 
If your space meets the requirements, than Übermat/Ditra uncoupling membrane is a great substrate choice for tile!

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