Wood ceilings are a great look for studies, foyers and many other rooms. One place you usually don’t see them is in the bathroom, because the moisture in the air can soften and rot wood surfaces. If you really want a wood ceiling in your bathroom, modern building materials give you some options. You can get ceiling boards that are treated and sealed against moisture, making them far more durable in the bathroom environment. This is still not recommended for full baths with showers in them, but for a half bath, it can work out just fine.
Find each joist in the bathroom ceiling with an electronic stud finder. Mark the positions of the joists with a level and pencil.
Set the board to the ceiling, at the starting edge, with the groove of the board facing the wall and the tongue side facing out into the room. Leave a half-inch space between the board and the wall.
Repeat for each ceiling board, building across the ceiling. Cut the last board lengthwise to fit against the far wall, leaving a half-inch gap there. Ceiling trim will cover the gaps.