Ash flooring/sub flooring

[bulldozerjoe]

I got a question, last spring i cut and skidded approx, 1200 square foot of ash.... I had them milled up in to 4 inch wide t and g... my flooring is complete and it's time to install... i ripped out all the carpet.  Under the carpet is 1/2 inch plywood... when I walk on it it makes noise... so my plan is to sheet over it with one side sanded plywood.    What thickness should I add over top... money is no object, I want it done right.... thanks

[Southside]

Is the plywood that is there just plywood or was it true underlayment in that it has a lap?  For sure you want to secure that layer down better than it is to eliminate the present squeak before you do anything more.  Will you have radiant heat under this floor?  I would lean toward another 1/2" underlayment, but the question becomes do you have room under your doors for the additional 1.25" rise that will create in the end.  

[bulldozerjoe]

It's just regular 1/2 plywood, no regular doors in my house.... there all being switched to farm house slider doors.... I'm just getting rid of the doors, drywalling and corner beading the opening and making farm house sliders out of butter nut that I cut

[bulldozerjoe]

The down stairs is gutted, getting all new cabinets and everything so I'm not worried about the height of everything