You haven't said what the subfloor is. You also need to describe the floor joist size and it's span between supports.
The tile you mentioned, is it ceramic tile?
Your plan will not work. You can't glue backerboard to vinyl tile. It needs to be screwed down to the surface as well as thinsetted.
Ron
The tile you mentioned, is it ceramic tile?
Your plan will not work. You can't glue backerboard to vinyl tile. It needs to be screwed down to the surface as well as thinsetted.
Ron