Floating floor with 50mmx50mm joists

[hugo_inside]

Is enough for floating a floor?? there are a HUGE diference between 100 mm x 50 mm and 50 x 50 mm joists?

is enough isolate the perimeter with rigid foam like polythyrene? the material in the pic:

[knightfly]

With the wood you were looking at, even 100mm is not best; 150 would be better, because with the same weight floor it lowers the m-a-m resonance quite a bit, and you need that to be sub-audible. Yours won't be, because this would take about 90mm concrete over about 150mm air space, resting on good EPDM rubber pads 25mm thick; so, on a budget, you do what you can to increase mass, widen air gaps, etc...

EPS (Expanded PolyStyrene) should work fine for perimeter isolation board; it's not too hard so won't bridge, and shouldn't rot or anything... Steve