QUESTION

Shower base Tile - Do Wall tiles need to sit on top of floor tiles in wet areas?

ANSWER

ANSWER - The lower course tile in a vertical wet area should be above the floor tile and there should be a joint there of 1/4" that is properly treated as a movement joint per TCNA EJ171 filled with a proper sealant to meet ASTM C920 (silicone, urethane, polysulfide).  Good Luck!