Bathroom Drywall: Which Board Goes Where

Can you put regular drywall in a bathroom?

Yes, on the walls and ceiling outside the tub and shower. The International Residential Code only sets board rules for the wet area and for board used as a tile base, so regular 1/2 in drywall meets code on a bathroom's dry walls, and Section R702.3.7 explicitly permits water-resistant board on ceilings. Where regular board does not belong is behind tile in the tub or shower, or anywhere water hits it directly.

Code is the minimum, not the recommendation. Moisture and mold resistant board costs a little more per sheet and holds up better in a room that gets steamy every day, especially one without a good exhaust fan. The picker above shows both: what the code allows and what we would buy.

Drywall above a shower

Above the tile line, the wall sees steam rather than spray, so moisture and mold resistant drywall is the normal choice from the top of the tile to the ceiling. Two cases change that. In a steam shower, or a shower enclosed to the ceiling with no fan, the humidity is continuous, and R702.3.7.1 rules out water-resistant gypsum board there, so run the backer and the tile to the ceiling. And never let the drywall run down behind the tile: the backer goes to the tile line, and the drywall starts above it.

What goes behind tile in a tub or shower

Section R702.4.2 of the 2024 IRC says backers for wall tile in tub and shower areas, and for wall panels in shower areas, must be one of the materials in Table R702.4.2: glass mat gypsum backing panel (ASTM C1178), fiber-reinforced gypsum panels (ASTM C1278), non-asbestos fiber-cement backer board (ASTM C1288 or ISO 8336, Category C), or non-asbestos fiber mat-reinforced cementitious backer units (ASTM C1325).

Paper-faced gypsum board, including the water-resistant kind often called green board, is ASTM C1396 and is not on that list. Section R702.3.7.1 adds that water-resistant gypsum backing board must not be used where there is direct exposure to water or in areas of continuous high humidity.

Section R327.2 (R307.2 in the 2021 edition) sets how high the wet-area finish goes: walls above bathtubs with shower heads and in shower compartments need a nonabsorbent surface to at least 6 ft above the floor. The calculator will not let you set the tile height lower than that when there is a shower.

The rest of the bathroom

Outside the wet area, moisture and mold resistant gypsum board is the usual choice. Section R702.3.7 explicitly permits water-resistant gypsum backing board on ceilings, and says it must not be installed over a Class I or II vapor retarder in a shower or tub compartment. Seal cut and exposed edges as the manufacturer recommends.

Mold resistant panels such as USG's Mold Tough line are a sensible upgrade for a bathroom without a good exhaust fan, but they do not turn the board into a tile backer for a shower.