What is the maximum spacing of ceiling joists in a shower with 1/2 inch water-resistance gypsum board with tile attached using adhesive?

What is the maximum spacing of ceiling joists in a shower with 1/2 inch water-resistance gypsum board with tile attached using adhesive?

• A. 16 inches
• B. 12 inches
• C. 18 inches
• D. 14 inches

Answer: (B)

When tiling a shower ceiling, the backing must stay very stiff because tile and adhesive add weight and moisture can soften the substrate over time. Using half-inch water-resistant gypsum board as the tile backing means joists should be spaced no more than twelve inches on center. Gypsum board in wet areas isn’t as rigid as cement board, so wider spacing allows too much flex, which can cause cracks in the tile or grout and bond failures. Keeping the joists at twelve inches on center provides the necessary stiffness to support the tile adequately. If you used cement board or added extra blocking, you could sometimes justify closer to standard larger spacings, but for this exact setup, twelve inches is the safe limit.

When tiling a shower ceiling, the backing must stay very stiff because tile and adhesive add weight and moisture can soften the substrate over time. Using half-inch water-resistant gypsum board as the tile backing means joists should be spaced no more than twelve inches on center. Gypsum board in wet areas isn’t as rigid as cement board, so wider spacing allows too much flex, which can cause cracks in the tile or grout and bond failures. Keeping the joists at twelve inches on center provides the necessary stiffness to support the tile adequately. If you used cement board or added extra blocking, you could sometimes justify closer to standard larger spacings, but for this exact setup, twelve inches is the safe limit.