floor structure advice please

Hi,

I am converting a garage to a small annex, and have had some confusing advice from my BCO, that I will have to follow, but hoping for some advice as to how to in certain areas.

There is a thick concrete slab base, under which there is a dpm - slight problem is that he made me dig a new foundation through that slab, and break the dpm, so a small section at the front doesn't have it under the slab.

He would then like me to put a new DPM over the top of the slab, then lay 100mm celotex/kinspan insulation. Onto that, he would like a floating, 18mm chipboard layer with the T&B glued, but not attached to anything else. I would like to end up with an engineered wood floor throughout - so was thinking I would then use a product like elastilon, and then lay the engineered floor onto that. Seems quite expensive?

Could I just put down some normal 3mm insulation ontop of the chipboard, and then float (only gluing in the the T&G) engineered hardwood floor over that? I will then have two different floating layers?!

Secondly, there are some, but not many, internal walls - to save having T bars, I am planning on flooring the whole open square space, and then screwing down the 4"x2" base and frames for the interior walls to the floor - rather than put the frames onto the chipboard, and then the engineered wood up to the frames, and then T bar through the doorways. Will screwing the wall frames down through the engineered floor and chipboard cause me problems with expansion etc?

All advice appreciated,

Steve