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Problem: Deterioration of drywall in high-moisture areas.

Cause: Excessive humidity and dampness in bathrooms, laundry areas and exterior soffits.

Moisture absorption can cause expansion and powdering of the gypsum core of the drywall sheets with the resultant of delamination of the paper face and mold growth.


  • Use water-resistant gypsum in damp areas. Most building codes now require "moisture-resistant backing" for ceramic and plastic tile on walls around bathtubs and showers.
  • Allow a 1/4 inch (7 mm) space between the drywall and the surfaces of the tub, shower floor or return as shown in Figure 69.
Installation Of Drywall Or Cement Board Over Bathtub
Figure 69 - Installation Of Drywall Or Cement Board Over Bathtub
  • To prevent problems at the bathtub, some builders use a cement-based board instead of a gypsum board as an underlay for ceramic tile, or they install a fiberglass tub enclosure.
  • Locate builders strap bathroom walls to allow an air space for improved drying.