ANSI tile standards cited by the Tile Council exclude OSB
Oriented strand board is sheathing made from wood strands glued with waterproof, heat-cured adhesives, layered in crossing directions like plywood. APA Voluntary Standard PS 2-92 is the performance standard the FAQ names for OSB and plywood.
The installation standard's exclusion
The Tile Council says the ANSI A108 edition it discusses, dated 1999 in that FAQ, specifically excludes OSB. The page does not claim tile can never last over an OSB subfloor. It says the trade still debates moisture, swelling before tiling, blocking, and bracing. Each setting-material maker has its own method. Some backer-board companies will stand behind their board over OSB only if their method is followed. Thinset manufacturers do not recommend installing ceramic tile directly to OSB.
Movement joints remain
Whatever sheet is under the tile, the FAQ repeats that movement joints are still required so the tile layer can expand and contract. The handbook is the place it sends readers for systems that include OSB.
Source
Fetched 2026-10-11 from Tile Council OSB FAQ. The sentences above follow that page. They are not a contractor promise.
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