New construction. Two floor residence - kitchen/dining area on first floor. Plan on putting 3/4" beadboard on ceiling. Will spot prime "knots" with BIN2 to seal knots and then go back and apply BIN2 to the boards to completely seal. Then will paint the displayed side with final (latex) paint. I do have R13 in joists above. (Reason ... radiant floor above calls for it.) QUESTION ... Should I place a plastic (4mil) vapor barrier above beadboards? I would guess normally this wouldn't be needed (or even desired) but I'm thinking that a kitchen puts out a ton of moisture. (Also, there is no drywall - code does not require it.) THANKS!