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For painted bathroom walls outside the tub or shower wet area, 1/2-inch (12.7 mm) moisture- and mold-resistant drywall is a practical starting choice. Use 5/8-inch (15.9 mm) panels where the specified assembly or framing requirements call for them. Products such as CertainTeed M2Tech are made for interior walls and ceilings in both thicknesses. They resist moisture; they are not a substitute for shower waterproofing. CertainTeed M2Tech technical sheet
For tiled shower walls and tub surrounds, choose an approved wet-area backer and water-management system—not ordinary greenboard with tile attached directly to it.
Choose by location
| Bathroom location | Material to specify | Controlling check |
|---|---|---|
| Painted walls outside direct-water exposure | Moisture- and mold-resistant gypsum board; often 1/2 in. (12.7 mm) | Framing spacing, finish and any required fire-rated assembly |
| Painted ceiling outside direct spray | Gypsum panel approved for the actual ceiling application | Thickness, support spacing, panel orientation and texture finish |
| Tiled shower or tub-surround walls | Approved cementitious, fiber-cement, glass-mat gypsum or fiber-reinforced gypsum tile backer | Wet-area approval and the complete water-management details |
| Shower using a proprietary membrane system | The substrate expressly accepted by that system | Manufacturer instructions and local acceptance of the assembly |
| Steam enclosure | A specifically approved steam-shower or steam-room assembly | Vapor-control requirements—not just a moisture-resistant board label |
For U.S. residential reference, 2024 IRC R702.3.7.1 prohibits water-resistant gypsum backing board where directly exposed to water or continuous high humidity. R702.4.2 lists the permitted tub-and-shower tile-backer categories: glass-mat gypsum to ASTM C1178, fiber-reinforced gypsum to ASTM C1278, fiber-cement to ASTM C1288 or ISO 8336 Category C, and fiber mat-reinforced cementitious board to ASTM C1325. These are model-code provisions; verify the edition and amendments adopted locally. 2024 IRC, Chapter 7
Greenboard or purple board?
Buy by product identification and technical sheet, not facing color. USG Mold Tough Firecode X uses green face paper; CertainTeed M2Tech uses blue-gray paper. Both identify moisture- and mold-resistant properties in their specifications. Color is not a universal performance grade. USG technical sheet · CertainTeed technical sheet
Regular drywall is not automatically prohibited throughout a bathroom. The distinction is exposure: the IRC prohibits interior gypsum board directly exposed to water, rather than requiring one special board everywhere in the room. Moisture- and mold-resistant board is the more targeted purchase for painted bathroom surfaces, but it still needs protection from persistent dampness. 2024 IRC R702.3.5
Likewise, Type X is a fire-resistance designation, not a waterproofing designation. Where a rated wall or ceiling is required, match the listed panel and complete assembly; thickness alone does not establish the rating. USG Mold Tough Firecode X technical sheet
Shower walls: backer board and waterproofing are separate choices
Cement board can withstand water without deteriorating, but that does not make the installed wall watertight. USG states that Durock cement board is vapor-permeable and requires a separate barrier over or behind it when waterproof construction is specified. Follow the chosen system’s details for joints, corners, penetrations and connections to the tub or shower base. USG Durock systems guide
There is a system-specific exception to blanket advice that “drywall never belongs in a shower”: Schluter permits KERDI membrane over drywall in tiled showers. That permission depends on the membrane assembly being completely waterproofed, including seams and connections. It does not mean any waterproofing coating can be applied over any drywall. Confirm the specified substrate and local acceptance before buying. Schluter KERDI instructions and drywall FAQ
Ceiling thickness: check the exact panel
Do not assume every 1/2-inch moisture-resistant board has identical ceiling limits. For example, CertainTeed’s August 2025 M2Tech sheet specifies these maximum framing spacings with panels perpendicular to framing:
- 1/2 in. (12.7 mm), without water-based texture: 24 in. (610 mm) on center.
- 1/2 in. (12.7 mm), with water-based texture: 16 in. (406 mm) on center.
- 5/8 in. (15.9 mm) Type X: 24 in. (610 mm) on center.
These are product-specific limits, not blanket permission for all greenboard or all ceiling assemblies. M2Tech technical sheet
Worked selection example
For a bathroom with 16-inch (406 mm) on-center wood framing, painted walls and ceiling outside direct spray, a tiled shower, and no required fire-rated assembly:
- Specify 1/2-inch moisture- and mold-resistant drywall for the painted walls outside the wet area.
- For the painted ceiling, 1/2-inch M2Tech installed perpendicular to framing falls within the published spacing limits above. Check current instructions if choosing another panel.
- Order the shower backer, waterproofing materials, fasteners and joint treatments as a separate compatible system.
Do not transfer the drywall fastener list to cement board: Durock, for example, prohibits drywall screws, drywall nails and drywall joint tape. USG Durock systems guide
Once the products and sheet sizes are settled, use the drywall sheet-weight chart to plan handling and transport.