Dimensions / Building materials / Drywall / Moisture-resistant drywall
Moisture-resistant drywall is paper-faced board with a water-resistant core and faces: 4 ft wide and 8 to 12 ft long at most makers, 1/2 or 5/8 in thick. In the US it may take up no more than 5% of its weight in water after 2 h under water. The IRC lets it serve as a tile base and on ceilings, but not as the tile backer in a tub or shower, where glass-mat, fiber-cement or cement board is listed. In Europe it is EN 520 Type H2, up to 10%: Siniat’s 12.5 mm Moisture Board weighs 8.45 kg/m² and takes tiles up to 32 kg/m² on studs 400 mm apart.
| Lengths at most makers | Water taken up, US limit | Siniat Moisture Board 12.5 mm |
|---|---|---|
| 8–12ft2438–3658 mm | 5%2 h | 8.45kg/m²H2 ≤ 10% |
Sources: USG, Gypsum Association, Siniat. Checked October 2026.
USG’s UltraLight Mold Tough on a bathroom wall is filled in. Enter your wall and sheets, where the board goes and a soaked sample, or switch to European rules; each check follows a figure or rule on this page.
Weigh a cut sample dry, soak it fully under water for two hours, wipe the surface and weigh it again.
Hung upright, a 10 ft wall takes 3 sheets 48 in wide, each reaching the 8 ft height; you have 3. Each sheet is 32 ft² and weighs about 43.2 lb at 1.35 lb/ft², 129.6 lb for 3; the Gypsum Association asks for two or more people to carry one.
USG UltraLight Mold Tough at 1.35 lb/ft² on a 10 ft bathroom wall is filled in.
IRC R702.3.7 allows water-resistant board as a base for tile, and IBC 2509.2 asks for it as the tile base on water-closet compartment walls. It still stays out of the tub and shower.
IRC R702.3.7 lets water-resistant board be the tile base outside the tub and shower.
612 g dry and 640 g after two hours under water: 4.58% taken up, within the 5% the Gypsum Association allows water-resistant board.
A 12 × 12 in cut is an example; 5% is the most US water-resistant board may take up.
Selling moisture board? Photograph a sheet and its face, mark the size, thickness, absorption and mold score in SizeMarker and send it with your quote.
Mark a photoMaker sheets; sizes and weights as each prints them.
| Board | Sizes | Weight, as printed | Absorption; face |
|---|---|---|---|
| USG Sheetrock UltraLight Mold ToughThis page | 4 ft × 8–12 ft (1219 × 2438–3658 mm); 1/2 in | 1.35 lb/ft² (6.59 kg/m²) | 5% at most after 2 h; green face |
| USG Sheetrock Mold Tough Firecode X | 4 ft × 8–12 ft; 5/8 in Type X | 2.2 lb/ft² | 5% at most |
| CertainTeed M2Tech | 4 ft or 54 in × 8, 10, 12 ft; 1/2 in, 5/8 in Type X | 1.6 / 2.2 lb/ft² | 5% at most; mold score 10 of 10; blue-gray |
| Georgia-Pacific ToughRock Mold-Guard | 4 ft × 8–16 ft; 1/2 in | 1.7 lb/ft² | Mold score 10; green face |
| Gold Bond XP | 4 ft × 8–12 ft; 1/2, 5/8 in | 1.5–1.6 lb/ft² at 1/2 in | 5% at most; purple face |
| American Gypsum M-Bloc | 4 ft × 8–12 ft; 1/2 in | Not printed | Mold score 10; blue face |
| PABCO Mold Curb Plus | 48 in × 8 or 12 ft; 1/2, 5/8 in | 1.7 / 2.3 lb/ft² | 5% at most; light blue face |
| Siniat Moisture BoardUK | 1200 × 2400, 2700, 3000 mm at 12.5 mm; 1200 × 2400 at 15 mm | 8.45 / 11.9 kg/m² | EN 520 Type H2; green both faces |
| Knauf Ausbauplatte GKBIGermany | 600 × 2000 or 2600 mm; 12.5 mm | 9.1 kg/m² | H2, 10% at most; green face |
| Rigips RBI 12.5Germany | 1250 × 2000 or 2500 mm | At least 8.5 kg/m² | H2 |
Sources: USG · USG · CertainTeed · Georgia-Pacific · National Gypsum · American Gypsum · PABCO · Siniat · Knauf · Rigips
Water-resistant board here means paper-faced board to ASTM C1396.
| Place | Allowed? | Rule |
|---|---|---|
| Tile base on walls outside the tub and shower | Yes | IRC R702.3.7: C1178, C1278 or C1396 board |
| Water-closet compartment walls under tile | Required | IBC 2509.2 |
| Ceilings | Yes | IRC R702.3.7, with no spacing limit; UFGS: supports 12 in apart at most |
| Tile backer in tubs and showers | No | IRC Table R702.4.2, IBC Table 2509.2: glass-mat (C1178), fiber-reinforced (C1278, IRC only), fiber-cement or cement backers |
| Over a vapor retarder in a tub or shower | No | IRC R702.3.7 (Class I or II); IBC 2509.3 |
| Direct water, continuous high humidity | No | IRC R702.3.7.1; IBC 2509.3 |
| Saunas, steam rooms, gang showers, pools | No | CertainTeed, Gold Bond, American Gypsum, PABCO |
Sources: IRC · IBC · UFGS · CertainTeed · National Gypsum · American Gypsum · PABCO
| Grade | Water taken up | Who prints it |
|---|---|---|
| US water-resistant board | 5% of its weight at most after 2 h under water | GA-235-10; USG, CertainTeed, Gold Bond, PABCO |
| EN 520 Type H2 | 10% at most in total after 2 h | Knauf, Siniat, Rigips |
| EN 520 Type H1 | Under 5% | Siniat LaDura |
Sources: Gypsum Association · Knauf · Siniat · Siniat
| Item | Figure |
|---|---|
| Tiles on Siniat Moisture BoardSiniat Drywall Manual | 32 kg/m² at most on studs 400 mm apart; Aquaboard 50 kg/m² |
| Siniat humidity classesSiniat Drywall Manual | Normal, and low to medium (bathrooms, toilets, kitchens): yes; high to severe (pools, spas, wet rooms, public showers): no |
| Ceiling tile backerPABCO | Framing 16 in apart for 5/8 in board, 12 in for 1/2 in |
| Ceiling framingCertainTeed M2Tech | 16 in for 1/2 in under a water-based texture, 24 in without; 24 in for 5/8 in Type X |
| Metal studs at tileUFGS 09 29 00 | 16 in apart at most |
| HeatUS makers | Avoid sustained temperatures over 125°F (52°C) |
| Room humidityKnauf GKBI | For rooms that stay at 70% relative humidity or less |
| In the check aboveOur calculation | A 10 ft wall ÷ 48 in = 2.5, so 3 sheets, 43.2 lb each; 612 g to 640 g is 4.58%. Europe: 2400 ÷ 1200 mm = 2 boards, 24.3 kg each; tiles of 25 kg/m² against 32; a 300 × 300 mm cut from 760 g to 820 g is 7.89% |
4 ft wide and 8 to 12 ft long at most makers, in 1/2 in and 5/8 in Type X: USG, Gold Bond, American Gypsum and PABCO stop at 12 ft, Georgia-Pacific’s Mold-Guard goes to 16 ft and CertainTeed also makes 54 in. In Europe Siniat sells 1200 × 2400 to 3000 mm at 12.5 mm.
Not as the tile backer in a tub or shower under the IRC and IBC: their tables list glass-mat, fiber-reinforced, fiber-cement and cement backers, and paper-faced board is not on them. Outside the tub and shower it may be the tile base.
Yes, IRC R702.3.7 allows it on ceilings and sets no spacing limit. The federal guide spec (UFGS) keeps supports 12 in apart at most, and PABCO asks for 12 in under tile with 1/2 in board.
In the US, 5% of its weight at most after 2 h under water (GA-235-10, and USG, CertainTeed and Gold Bond print the same). EN 520 Type H2 allows 10%, Type H1 under 5%, so a European H2 board is not the same grade.
Siniat allows 32 kg/m² on its Moisture Board with studs 400 mm apart, and 50 kg/m² on Aquaboard. US makers give tile use by area, dry or limited water, rather than by weight.
It depends on the maker: USG and Georgia-Pacific use green paper, CertainTeed blue-gray, Gold Bond purple, American Gypsum blue and PABCO light blue; Siniat and Knauf use green.
Buyers ask for the size and thickness, the face colour, the water absorption with its test (2 h, by weight), the mold score, the type (ASTM C1396 water-resistant, EN 520 H1 or H2), the weight, where the board may and may not go, and sheets per pallet. Mark the real sheet and its face on your own photo in SizeMarker, as in the picture at the top, and send one product card for WhatsApp or WeChat.
