: I am building a new shower stall in the basement and am putting 1/2" exterior plywood on the studs, a vapor barrier, and hardibacker board and then ceramic tile. Is it okay to use the plywood? Please advise as soon as possible.
: Thank you very much.

Hans,
As I understand it. A good job will include a vapor barrier on the studs only.
The backer board works best when it can dry on the back side. Installers have told me to leave the vapor barrier off between the studs. If you have 1/2" backer board, you don't need the plywood.