Flooring Movement

I have walked upon thousands of timber floors, and owned a fair few too. But it's not until I took a critical look at the floor I am laying that I have paid close attention to the movement in it.

130 x 19 T&G Tassie Oak on F17 joists at 450 centres, glued to joists and top-nailed. If I apply body weight to the edge of a laid board, midway between joists, I get vertical movement of perhaps 0.5mm of the loaded board against the other. Milling appears to be within spec, although the way I read the spec there can be up to 1.1mm gapping between tongue and groove (tonge 6.5mm thick, groove 7.0mm wide, and a tolerance of 0.3mm for each). That would appear to allow 1mm of deflection.

Any thoughts about whether this is normal? I don't appear to have joist or bearer movement, and the boards are cramped reasonably tight with a Tbar cramp.


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