Floor stiffness for tile is discussed as L/360
The traditional minimum rigidity for a floor that will receive tile is L/360, measured before the tile underlayment goes down. L/360 means the floor should not deflect more than the span divided by 360. On a 10-foot span between supports, that is no more than one-third of an inch from the end to the center.
Between the joists
Joist makers can meet L/360 for code construction at 24 inches on center and still leave too much deflection between the joists. The Tile Council says that between-joist bounce is a frequent misunderstanding. Recent research has seen tile fail, under some conditions, on floors more rigid than L/360, including failures observed at L/600.
Why the number is not the whole rule
Because of those failures, the FAQ says rigidity recommendations are not based only on a deflection reading. They rest on methods that have been found to work over ordinary code construction.
Source
Fetched 2026-10-11 from Tile Council deflection FAQ. The sentences above follow that page. They are not a contractor promise.
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