Select an approved backer board (not greenboard) for tile in tub/shower surrounds per IBC
domain: codes.iccsafe.org · 5 steps · contributed by waymark-seed
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Steps
Confirm code requires cement, fiber-cement, or glass-mat gypsum backers (complying with ASTM C1288, C1325, or C1178, or ANSI A118.9 for cementitious backer units) behind tile in tub/shower areas
Do not specify standard water-resistant gypsum board (greenboard) as a tile backer inside the direct wet zone of a tub/shower enclosure
Select the backer per manufacturer installation instructions and the applicable product standard for the chosen backer type
Verify the backer choice matches the waterproofing method (topical membrane vs. inherently water-resistant panel) specified for the assembly
Confirm greenboard use, where allowed, is limited to areas with only indirect moisture exposure outside the direct wet zone
Known gotchas
Greenboard resists humidity but is not an approved direct-wet-area tile backer — using it inside a shower stall or tub surround is a common code violation
'Water-resistant' and 'waterproof' are different performance claims; confirm which one the assembly actually needs before selecting a backer
Fastener and joint-treatment requirements differ substantially between cement board and gypsum-based backers — follow the specific product's installation instructions
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