I was laying out tile in a half bathroom before wondering if I should tile under the door or not. The picture below shows the tile (top), plywood subfloor where the door will be (middle), and laminate flooring in the hallway (bottom).
There is a cement backerboard underneath the tiles — this strip of plywood is all that's left of the old subfloor. The hallway leading to the bathroom has laminate floor over what I think may be asbestos tile. To keep those tiles encapsulated I plan to put some sort of molding or threshold between the two rooms.
The height of the laminate floor above the plywood is about 3/4", and I expect the 5/16"-tall tiles to be about 1/2" above the plywood once the thinset mortar is down.
So: should I tile all the way to the laminate floor (under the bathroom door), or leave the tiles as they are in the picture? Seems like the latter solution would make it easer to put in a threshold/molding, but it also seems odd for the flooring under the door to be nonexistent.
Best Answer
If you are planing on adding a threshold (also called a transition strip) and you are sure it will be wide enough to cover the gap between the laminate and the tile, then no, there is no reason to add the tile in that gap.
As you noted with the tile there nailing the transition strip is nearly impossible. (Could only be nailed on the hall side plus the door frame edges, you'd be mainly relining on glue.)
If you are worried about the empty space (some transition strips are way too thin to bridge a gap like that) then just put plywood in the gap between the tile and the laminate. That makes the tile job easy and the threshold piece secure.
To determine the thickness of the needed plywood measure the height of the finished tile and pick something close or a bit under, not over (in your case sounds like ½ inch will work.)