"Floor Framing Under Tile: L/360 and the Joist Span Table" is lesson 2 of 7 in the Tile (C-54) Learning Hub. It opens with "Tile Cannot Bend" and works through 5 short steps, then a worked example you can check yourself against.
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The worked example in the course applies this lesson to a realistic job in 5 steps, from "Find the loads and the limit" through "Note what dead load did".
Tile, thin-set, and grout are rigid. If the joists under a tile floor sag too much when people walk on it, the tile cracks, the grout line breaks, and the bond fails. Before you set tile over a wood floor you confirm the framing is stiff enough, and a bad frame cannot be saved by adding more mortar or another layer of underlayment. The numbers you can point to in the California code are in the Residential Code, and this lesson uses only those.
2025 CRC Section R301.7 says the allowable deflection of any structural member under the live loads in Sections R301.5 and R301.6 (or wind) shall not exceed the values in Table R301.7. For floors the printed limit is L/360, where L is the span length (footnote b: for a cantilever, L is twice the cantilever length). The table prints stricter "brittle finish" values only for ceilings (L/360) and exterior walls, and it has no separate row for tile floors or stone floors. A tighter limit for tile or stone can come from the project specifications or an engineer, but it is not printed in this table.
The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.
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