Asking how much the floor under tile moves
Tile is rigid and brittle. It has no ability to flex, so when the floor beneath it moves, something has to give, and the weakest line in a tile floor is the grout joint. That is why cracked grout in a straight line across a room is a structural report, not a maintenance problem. Deflection is how much a floor bends between its supports under load, and it depends on joist depth, joist spacing, span and the thickness of the deck on top. The Ontario Building Code sets minimum subfloor thickness against joist spacing in Article 9.23.14.5, and the requirement rises as bays get wider: a 610 mm bay needs a thicker deck than a 406 mm bay, and oriented strand board has to be thicker than plywood for the same performance. We measure the spacing, measure the deck and walk the floor before quoting, because adding a layer of plywood is inexpensive now and impossible later.



