Hi everyone!

New to this most informative forum, and here goes for my first post/question!

Done a little bit of research and it seems the informed opinion that marine, or at least exterior grade ply of about 1/2 inch thick should be screwed down first to give a good base.

I am a little concerned that this and the thickness of tiles and adhesive would raise the level of the floor too much, (somewhere around an inch) such that it might be be significantly higher than the adjoining landing floor.

As the existing floorboards are in less than perfect condition, would it make sense to remove them and replace the entire area to be tiled with a slightly thicker plywood sheet screwed directly to the joists, and then tile over that?

If so what thickness would be adequate? - It would make life easy if I could use the same thickness as the existing floorboards - the fact that it would be a single sheet and screwed down instead of nailed would mean that it ought to be stronger and more rigid than the existing floor, but would that be enough?

As the bath is already installed and I do not propose tiling underneath it I would be keeping the exising floorboards under the bath. It is also a fairly small bathroom so the area to cover is not huge.

Many thanks for your input!