What thickness is the standard water-resistant gypsum board used in showers?

• A. 1/2 inch
• B. 5/8 inch
• C. 3/4 inch
• D. 1 inch

Answer: (B)

Moisture resistance plus stiffness is what matters for shower walls. Five-eighths of an inch of moisture-resistant gypsum board provides the right balance: it’s thick enough to stay rigid under tile and resist sag or edge damage during installation, yet not so thick that it becomes unwieldy or costly. This thickness gives a solid substrate for fasteners and helps prevent cracking of grout and tiles by reducing deflection. Lighter thicknesses can flex and fail to support heavy tile work, while thicker gypsum boards are unnecessary for typical shower installations and add extra weight. For showers, the standard choice is five-eighths inch.