Bill Vincent or the folks over at The John Bridge Forum ought to be able to describe what you need as a suspended wood floor system to have a successful porcelain tile job.

In short, however, the particle board would need to go. It can be neatly removed up to cabinets, but you need the flush cut saw and other special tools to do that.

Consult with your flooring contractor. He or she ought to know how to do successful installations.

Thank you! That is a great tile forum. My contractor says I am over educating myself to the point of anxiety. But I know from experience that I have to stay on top of things. We have had some poor work done. I found my cntractor through a referral group.... so I am going to trust him.

I'm going to do what was suggested by TileTech in the message just above. But, I am also removing the tub. Should I remove tub and put this flooring down in the whole tiny bathroom then install new tub on top of it and then tile exposed part? Or what should go under the tub if not. Thank you for any help.

What is the joist size ans span?

If the joists are small or at the span limit for their size THEY will flex more than allowed.

Lisa~Just to play it safe, I'd remove the tub and do as I suggested for the rest of the floor. You might be able to get by with just the two layers of plywood under the tub.....but you will want to "Bed" the tub with brick morter or expanding foam. Don't go too crazy with the foam....you just want to make a solid bed for the tub.